Pathways toward commercial perovskite/silicon tandem photovoltaics

Synergistic Solvent and Composition Engineering of Perovskites for Tandems on Industrial Silicon

Wide-bandgap perovskites based on mixed formamidinium-cesium cation and iodide-bromide halide are promising materials in the top cells that are well-matched with crystalline silicon bottom cells to construct efficient tandem photovoltaics. Nevertheless, mixed cation-halide perovskite films with submicron film thickness suffer from poor crystallinity with inhomogeneous and undesirable phases, owing to the presence of multiple pathways of crystal nucleation and phase transition. Herein, we propose a synergistic solvent and composition engineering (SSCE) strategy to regulate the solvated phases and manipulate the transition pathways simultaneously. The resultant mixed cation-halide perovskite film shows optimizing crystallization and desired phase structure with suppressed nonradiative recombination and improved phase stability under aging stresses. Consequently, the SSCE strategy enables the tandem cells based on industrially ultrathin silicon wafers (120 µm) to achieve a certified stabilized power conversion efficiency of 31.0%. Those encapsulated devices maintain 90% of their initial performance after 1200 h continuous operation.

Achieving 32% Efficiency in Perovskite/Silicon Tandem Solar Cells with Bidentate-Anchored Superwetting Self-Assembled Molecular Layers

The inhomogeneity of hole-selective self-assembled molecular layers (SAMLs) often arises from the insufficient bonding between anchors and metal oxide, particularly on textured silicon surfaces when fabricating monolithic perovskite/silicon tandem solar cells (P/S-TSCs) and the hydrophobic carbazole complicates the fabrication of high-quality perovskite films. To address this, we developed a novel bidentate-anchored superwetting aromatic SAM based on an upside-down carbazole core as a hole-selective layer (HSL), denoted as ((9H-carbazole-3,6-diyl)bis(4,1-phenylene))bis(phosphonic acid) (2PhPA-CzH). The bisphosphonate-anchored exhibited enhanced adsorption capabilities and efficient hole extraction/transport, and the reversely substituted carbazole ring contributed a friendly super wetting underlayer that enabled high-quality perovskite films with minimized energetic mismatches, which 2PhPA-CzH played a pivotal role in dual interfacial energy regulation. Through these advancements, the optimized wide-bandgap (1.68 eV) PSCs demonstrated an improved PCE of 22.83% and excellent stability with T90 exceeding 1000 h under damp-heat conditions (ISOS-D-3, 85% RH, 85 °C), representing one of the best performances for SAMs as HSL-based PSCs. Notably, 2PhPA-CzH-functionalized recombination layers extended to submicron-pyramid texture SHJ to fabricate P/S-TSCs, achieving an impressive efficiency of 32.19% at an active area of 1 cm2 (certified 31.54%) while maintaining excellent photostability. This work offers guidance for designing multidentate-anchored SAMs to realize record PCE and excellent stability in P/S-TSCs.

Engineering perovskite solar cells for photovoltaic and photoelectrochemical systems: strategies for enhancing efficiency and stability

Solar-driven fuel production, including photovoltaic-electrochemical (PV-EC) and photoelectrochemical (PEC) water splitting as well as CO2 reduction reaction (CO2RR), presents a viable approach to mitigating carbon emissions. One of the major obstacles in developing efficient PV-EC and PEC systems lies in identifying suitable photoabsorbers that can effectively harness solar energy while maintaining stability under operating conditions. Despite their intrinsic instability in such environments, halide perovskites have garnered significant attention as promising photoabsorbers due to their exceptional optoelectronic properties, which are essential for facilitating efficient electrochemical reactions. This review first provides a concise overview of the mechanisms underlying water splitting and the CO2RR, followed by an examination of the structural configurations and performance evaluation metrics of PV-EC and PEC systems. Next, the design and engineering of perovskite solar cells (PSCs) are explored, with an emphasis on optimizing light absorption, charge transport layer engineering, and addressing stability issues. Recent advancements in enhancing the efficiency and operational stability of PV-EC and PEC systems incorporating PSCs are then summarized. Finally, key challenges currently being addressed in the field are discussed, along with perspectives on future research directions. This review aims to support researchers in further advancing this technology toward the commercial production of green hydrogen.

Compacting Molecular Stacking and Inhibiting Self-Aggregation in Fullerene Transporting Layer for Efficient and Stable Perovskite Solar Cells

The underdevelopment of electron transport layer (ETL) materials remains a critical bottleneck limiting the overall photovoltaic performance of inverted perovskite solar cells (PSCs). Fullerene derivatives, such as PCBM, are widely employed ETL materials in PSCs due to their excellent electron affinity and energy level alignment with the perovskite layer. However, PCBM suffers from high energy disorder, self-aggregation predilection, and insufficient defect passivation ability, leading to significant charge carrier recombination and accumulation at interfaces. Herein, a phosphate-substituted fullerene derivative, FuPE, is developed to enhance the performance of PCBM-based ETLs for PSCs. Incorporating FuPE efficiently compacts molecular stacking, enforces crystallinity and intermolecular interaction, suppresses self-aggregation, and improves interfacial compatibility of the FuPE:PCBM blend. Such endows the FuPE:PCBM blend film with enhanced electron mobility (0.183 cm2 V-1 s-1), lower trap density, more uniform film morphology, and superior defect-passivation ability, compared to the PCBM pristine one. Consequently, PSCs employing FuPE:PCBM as the ETL achieve reduced trap-assisted recombination, enhanced charge carrier extraction, and thus a remarkable power conversion efficiency exceeding 26% alongside improved operational stability. This work highlights an effective strategy for optimizing fullerene-based ETLs, advancing the development of highly efficient and durable PSCs.

Perovskite Photovoltaic Hydrogen Production from Seawater with Solar to Hydrogen beyond 14% and Techno-Economic Evaluation

Photovoltaic (PV) hydrogen production from seawater enables solar energy to be stored as hydrogen fuel; highly active electrocatalysts for the oxygen evolution reaction (OER) are critical. The interplay between PV output and the OER performance is crucial for achieving cost-effective and efficient hydrogen production. Here, we detail the synthesis of transition metal oxide catalysts through a rapid electrodeposition technique. Notably, the CoFe/indium tin oxide (ITO) demonstrated superior OER activity in a simulated seawater environment, with an overpotential of merely 268 mV at 10 mA/cm2. Unassisted perovskite PV hydrogen production coupled by tandem perovskite solar cells (PSCs) and CoFe/ITO//Pt water splitting cell achieved a peak operating current density of about 11.53 mA/cm2 and a solar to hydrogen efficiency of 14.18%. Furthermore, we meticulously crafted an extensive perovskite solar module framework for hydrogen production by scrutinizing the operational mechanisms of various active areas within the PSCs and the OER catalysts throughout the electrolytic process. A comprehensive techno-economic analysis has been conducted, which has unveiled that the levelized cost of hydrogen for the perovskite PV hydrogen production system was approximated at 7.17 $/kg. This finding provides both theoretical underpinning and practical direction for the advancement of solar hydrogen fuel production, underscoring its potential as a sustainable energy solution.

Modified Near-Infrared Annealing Enabled Rapid and Homogeneous Crystallization of Perovskite Films for Efficient Solar Modules

Currently, perovskite solar cells have achieved commendable progresses in power conversion efficiency (PCE) and operational stability. However, some conventional laboratory-scale fabrication methods become challenging when scaling up material syntheses or device production. Particularly, the prolonged high-temperature annealing process for the crystallization of perovskites requires a substantial amount of energy consumption and impact the modules' throughput. Here, we report a modified near-infrared annealing (NIRA) process, which involves the excess PbI2 engineered crystallization, efficiently reduces the preparation time for perovskite active layer to within 20 s compared to dozens of min in conventional hot plate annealing (HPA) process. The study showed that the incorporated PbI2 promoted the consistent nucleation of the perovskite film, leading to the subsequent rapid and homogeneous crystallization at the NIRA stage. Thus, highly crystalized perovskite film was realized with even better crystallization performance than conventional HPA-based film. Ultimately, efficient perovskite solar modules of 36 and 100 cm2 were readily fabricated with the optimal PCEs of 22.03% and 20.18%, respectively. This study demonstrates, for the first time, the successful achievement of homogeneous and high-quality crystallization in large-area perovskite films through rapid NIRA processing. This approach not only significantly reduces energy consumption during production, but also substantially shortens the manufacturing cycle, paving a new path toward the commercial-scale application of perovskite solar modules.

Transitioning Photovoltaics to All-Perovskite Tandems Reduces 2050 Climate Change Impacts of PV Sector by 16

Solar photovoltaics (PVs) are projected to supply up to 79% of global electricity by 2050. The mass production of energy-intensive silicon PV may lead to significant environmental impacts and material demands. Adopting metal halide perovskite tandem PV can further enhance the sustainability of the PV sector due to their potentially higher efficiency yet lower fabrication emissions than silicon PV. Here, we assess the climate and material demand impacts of perovskite tandem deployment on global and regional PV sectors from 2030 to 2050. In addition to the deployment of perovskite tandem into the silicon-dominated PV sector, we consider the fast, slow, and no transitions from perovskite-silicon tandem as a stepping stone to the final all-perovskite tandem PV. The transition can reduce up to 0.43 Mt tin requirement and 16.2% of cumulative carbon emissions from the PV fabrication process. Even without all-perovskite deployment, perovskite-silicon PV can still generate up to a 10.8% cumulative carbon reduction compared to silicon PV scenarios. Besides, the deployment of perovskite tandem systems can reduce energy costs by up to 21.2%, achieving a levelized cost of electricity (LCOE) as low as 3.66 cents/kWh. Achieving these results requires replacing resource-limiting components, such as substituting indium-tin-oxide with fluorinated-tin-oxide analogs.

Unraveling the Operation Degradation Mechanism of Positive Bias Interface in Perovskite Solar Cells

The interfaces of perovskite film are most susceptible to degradation during perovskite solar cell (PSC) operation. Previous efforts mainly focused on the degradation pathways of either independent upper or buried interfaces, while thorough and meticulous consideration of the disparity in electrical bias and light field difference between these interfaces during operation still remains unexplored. Herein, it is uncovered that the electrical bias significantly influences the operation degradation of perovskite interfaces in both n-i-p and p-i-n PSCs. More pronounced degradation has been found at the positive bias interface (perovskite/hole transporting layer interface) compared to the negative bias interface (perovskite/electron transporting layer interface). In the case of n-i-p PSCs, more severe degradation is mainly due to the electrochemical oxidation reaction catalyzed by diffused gold with high concentration of photogenerated holes at the positive bias interface. For p-i-n PSCs, the electrochemical oxidation reaction still occurs at the positive bias interface, inducing direct oxidation of silver with iodine species and photogenerated holes into silver iodide. Moreover, the incident light synergistically contributes to positive bias interface degradation in p-i-n PSCs. This work provides valuable guidance for understanding the degradation mechanism of different perovskite interfaces under different physical and chemical environment during device operation.

Fluorination-Assisted Interfacial Dipole for CsPbI3 Perovskite Solar Cells with Over 22% Efficiency

Inorganic CsPbI3 perovskite attracts widespread attention in photovoltaic applications due to its superior thermal stability and optoelectronic properties. However, CsPbI3 perovskite solar cells (PSCs) still suffer from severe energy losses due to interface nonradiative recombination and undesirable charge carrier transfer, predominantly limiting their photovoltaic performance. Herein, an interfacial dipole engineering is introduced for CsPbI3 PSCs, in which azetidinium chloride (Az) and its fluorinated derivative 3,3-difluoroazetidinium chloride (DFAz) are employed to manipulate the interface properties of PSCs and thus diminish energy losses. Systematically theoretical calculations and experimental studies reveal that the fluorination-assisted ammonium molecule could form a stronger interaction with perovskites and thereby arrange the dipole alignment on the superficial layer of perovskites, which could simultaneously ameliorate the passivation effect and energy level alignment of the perovskite and hole transport layers, thereby suppressing interface recombination. Meanwhile, the coordinated bonding between the ammonium and hole transport layer facilitates charge transfer at the heterojunction interface by offering additional carrier transport channels. Consequently, the CsPbI3 PSCs deliver a high efficiency of up to 22.05%. This work provides important design principles of interface engineering for high-performance solar cells to minimize energy losses.

Bifacially Reinforced Self-Assembled Monolayer Interfaces for Minimized Recombination Loss and Enhanced Stability in Perovskite/Silicon Tandem Solar Cells

Perovskite/silicon tandem solar cells have shown higher power conversion efficiencies (PCEs) than single-junction cells. However, their record PCE still falls short of the theoretical maximum, and their stability is significantly lower than that of crystalline silicon solar cells. These challenges stem from the substantial losses in open-circuit voltage (VOC) and the instability of wide-bandgap perovskite devices, which are mainly caused by nonradiative recombination and degradation at the heterojunction interfaces, respectively. Specifically, the weak adhesion between indium tin oxide (ITO) and self-assembled monolayers (SAMs), along with inadequate interactions between the SAMs and the perovskite, contributes to this instability. Herein, a novel SAM material, 4-(11H-benzo[a]carbazol-11-yl)butyl (4-PhCz), has been developed to bifacially reinforce interfaces by enhancing SAM coverage on ITO and strengthening the interactions between SAM and perovskites. The resulting 1.67 eV perovskite solar cell (PSCs) achieves a VOC of 1.273 V with a low voltage loss of 0.397 V relative to the bandgap and a PCE of 22.53%. The 4-PhCz-based perovskite/silicon tandem cell achieves a VOC of 1.96 V and a PCE of 31.26%, retaining 92% of its initial efficiency after 1000 h of maximum power point tracking (MPPT) under 1-sun illumination in a nitrogen atmosphere at 25 °C.

Ambient Air Deposition Allows Reaching Record Light Use Efficiency in FAPbI3 Perovskite Solar Cells

Semi-transparent solar cells represent an exciting opportunity for sustainable energy production, thanks to the possibility of being integrated into buildings and urban environments, effectively exploiting the already existing space. Perovskite solar cells (PCSs) are ideal candidates, offering high power conversion efficiencies (PCEs) combined with a tuneable band gap and adjustable thickness, which allow a convenient modulation of the average visible transmittance (AVT). However, balancing high PCE and high AVT is a challenging target. This study uncovers that depositing the perovskite layer based on Formamidinium Lead Iodide (FAPbI3) thin films in ambient air, rather than in a nitrogen-controlled atmosphere, allows an increase in the AVT value of up to > 40% while also enhancing the photovoltaic performance and stability. The optoelectronic quality of the as-obtained perovskite layer is substantially enhanced, showing fewer defects and a superior morphology. As a result, the air-deposited devices exhibit higher efficiency, which, combines with the enhanced AVT, results in a champion device with a light use efficiency (LUE) of 4.2%, having a PCE of 13.8% and AVT of 30.4%. The record LUE value and the possibility of being deposited in ambient air conditions pave the avenue toward the real-world application of semi-transparent PSCs.

Homogenization and Rapid Oxidation of Spiro-OMeTAD with Ionic Liquids for Efficient Perovskite Solar Cells

Spiro-OMeTAD is widely recognized as the most effective hole transport layer (HTL) for n-i-p perovskite solar cells (PSCs), which typically requires doping with LiTFSI to overcome its low inherent conductivity. However, the doping takes a prolonged oxidation (≈24 h) in an ambient atmosphere, hindering the commercial development. Moreover, the aggregation of LiTFSI leads to poor conductivity and accelerated degradation of the HTL, which are often ignored. This study introduces the long-chain ionic liquid 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (OMIMTFSI) as a multifunctional additive to mitigate the aggregation of LiTFSI and promote the oxidation of Spiro-OMeTAD simultaneously. The strong electrostatic interactions between OMIM+ and LiTFSI, coupled with the dispersion effect of OMIM+ in chlorobenzene, effectively hamper the aggregation of LiTFSI, beneficial for uniform doping and enhanced conductivity. The OMIM+ also facilitates rapid oxidation of Spiro-OMeTAD by attracting lone pair electrons from the triphenylamine group. As a result, the power conversion efficiency of PSCs processed in air is significantly improved from 21.48% to 24.04% with enhanced stability, maintaining over 80% of initial values after storing in air for 1360 h or under light and heat treatment for 500 h. This strategy provides valuable insights of designing lithium salt-doped Spiro-OMeTAD for efficient and stable PSCs.

Synergic MXene and S-benzyl-L-cysteine Passivation Strategies for Wide Bandgap Perovskite Solar Cells for 4T Tandem Applications

Bilayer nickel oxide (NiOx)/[2-(3,6-dimethoxy-9H-carbazol-9yl) ethyl] phosphonic acid (MeO-2PACz) hole transport layers have become attractive for perovskite solar cells and tandem architectures. However, challenges such as the instability of NiOx ink, hole accumulation, and trap-assisted non-radiative recombination at the interface remain major drawbacks for using NiOx/MeO-2PACz HTL bilayer. In this work, two synergic strategies are employed to address these issues such as the doping of the NiOx ink with niobium (Nb)-based MXene) and the introduction of S-benzyl-L-cysteine (SBLC) molecule to passivate the MeO-2PACz/perovskite interface. These modifications effectively reduced defect states in the perovskite layer and enhanced the dipole moment of MeO-2PACz, minimizing the valence band offset at the MeO-2PACz/perovskite interface with the reduction of the charge recombination rates. Consequently, the target PSC device, made of 1.68 eV-bandgap perovskite, demonstrated a power conversion efficiency (PCE) of 19.5% and improved stability compared to the control device when tested under ISOS protocols. Furthermore, semi-transparent (ST) PSCs have been fabricated for application in 4T tandem perovskite-silicon cell showing PCE of 18.15% and 27.95% in single-junction and in tandem architectures, respectively. These findings demonstrate the effectiveness of combining strategic doping and passivation techniques for inverted PSCs enhancing the device performance without discarding long-term stability.

Optimizing Molecular Packing and Interfacial Contact via Halogenated N-Glycidyl Carbazole Small Molecules for Low Energy Loss and Highly Efficient Inverted Perovskite Solar Cells

Nonideal interfacial contact and non-radiative voltage loss in self-assembled monolayers (SAMs)-based inverted perovskite solar cells (PSCs) limit their further development. Herein, two carbazole-based molecules with different halogen atoms (X-OCZ, X = Cl or Br) are developed as efficient interfacial regulators. The halogen effect not only finely modulates the molecular packing, crystallinity, and surface contact potential of the MeO-2PACz analogue via self-induced intermolecular interactions but also significantly influences the subsequent crystal growth of perovskite, thus resulting in the formation of high-quality films with enhanced crystallinity, improved energy level alignment, and depressed non-radiative recombination. Importantly, the Cl-OCZ-mediated device exhibits a minimal interfacial carrier transport energy barrier of 0.10 eV and an impressive charge collection efficiency of 93.6%. Moreover, the target device (aperture area: 0.09 cm2) shows an exceptional efficiency of 26.57% (certified 26.4%) along with enhanced thermal and operational stability. The strategy is also extended to large area devices, delivering efficiencies of 25.0% for a 1 cm2 device and 22.9% for a 12.96 cm2 minimodule. This study highlights the halogen role of interfacial small molecules in optimizing molecular packing and interfacial contact toward highly efficient PSCs with minimized energy loss and non-radiative recombination.

Luminescence-Based Implied Voltage Imaging of Tandem Solar Cells Using Bandpass Filters

A luminescence-based technique is demonstrated for selectively imaging the implied voltages of tandem solar cells. The luminescence emission is captured using a narrow bandpass filter so that the detected luminescence signal is insensitive to the optical properties of the device, thus, revealing the variations in the implied voltages. The proposed method is validated through simulation and experiments conducted on two-terminal perovskite/silicon tandem solar cells with different structures, optical properties, and compositions (e.g., different bandgaps for the perovskite cells). Implied voltage images of each sub-cell can be determined with a maximum relative error of 1%. The proposed technique can also be used to obtain local current-voltage curves. The method is expected to be a valuable tool for optimizing the performance of tandem solar cells, scaling up tandem devices, investigating local defects, and predicting the ultimate device performance.

Tailoring Crystal Growth Regulation and Dual Passivation for Air-Processed Efficient Perovskite Solar Cells

Hybrid metal halide perovskite solar cells (PSCs) are emerging as highly competitive next-generation photovoltaics due to their excellent performance and low production cost. However, the construction of high-efficiency PSCs typically requires an inert nitrogen environment within a glove box, inadvertently increasing manufacturing costs and hindering the transition from lab-scale to industrial-scale production. In this work, an air ambient fabrication of pure α-phase FAPbI3 PSCs with high-efficiency and stability, utilizing a dual-functional engineering strategy assisted by 3-Guanidinopropionicacid (3-GuA) is reported. 3-GuA assists in managing excess PbI2 and promotes the formation of high-quality FAPbI3 films via intermolecular exchange. Simultaneously, the existence of 3-GuA minimizes the defects and stabilizes the resulting perovskite films. As a result, the ambient-air fabricated PSCs achieve a power conversion efficiency (PCE) of 24.2% with negligible hysteresis and excellent stability. Additionally, these devices demonstrate superior reproducibility, offering valuable guidance for future advancements in this technology.

Machine Learning-Assisted Prediction and Control of Bandgap for Organic-Inorganic Metal Halide Perovskites

Perovskite materials have wide application prospects in many fields due to their tunable and designable band gap characteristics. Machine learning has obvious advantages in quickly and effectively discovering new materials. However, noise interference within data sets frequently hinders the ability of traditional predictive and evaluative techniques to satisfy practical requirements. This study introduces an outlier removal strategy to examine the influence of varying degrees of outlier exclusion on the generalization performance of the learning model followed by the determination of the optimal configuration. The results indicated that the gradient boosting regression tree (GBRT) algorithm yielded a mean absolute error (MAE) of 0.0287, a mean squared error (MSE) of 0.0014, a root mean squared error (RMSE) of 0.0377, and an R-squared (R2) value of 0.979, demonstrating superior performance with a minimal prediction error compared to alternative algorithms. Moreover, the Shapley Additive Explanation (SHAP) method was utilized to elucidate the impact of various chemical compositions on the desired band gap, revealing that the ratio of I exerts the most significant influence, with the Pb, Br, and Sn ratios exerting a subsequent effect. We further investigated the effect of different chemical composition ratios on the band gap, and the experimental results show that individual elements maintain stability within particular proportionate bounds, thereby offering critical data to underpin band gap control strategies. This study provides new valuable insights for realizing accurate prediction and effective control of band gaps.

Steering perovskite precursor solutions for multijunction photovoltaics

Multijunction photovoltaics (PVs) are gaining prominence owing to their superior capability of achieving power conversion efficiencies (PCEs) beyond the radiative limit of single-junction cells1-8, for which improving narrow-bandgap (NBG) tin-lead perovskites is critical for thin-film devices9. Here, with a focus on understanding the chemistry of tin-lead perovskite precursor solutions, we find that Sn(II) species dominate interactions with precursors and additives and uncover the exclusive role of carboxylic acid in regulating solution colloidal properties and film crystallization and ammonium in improving film optoelectronic properties. Materials that combine these two functional groups, amino acid salts, considerably improve the semiconducting quality and homogeneity of perovskite films, surpassing the effect of the individual functional groups when introduced as part of separate molecules. Our enhanced tin-lead perovskite layer allows us to fabricate solar cells with PCEs of 23.9%, 29.7% (certified 29.26%) and 28.7% for single-junction, double-junction and triple-junction devices, respectively. Our 1-cm2 triple-junction devices show PCEs of 28.4% (certified 27.28%). Encapsulated triple-junction cells maintain 80% of their initial efficiencies after 860 h maximum power point tracking (MPPT) in ambient. We further fabricate quadruple-junction devices and obtain PCEs of 27.9% with the highest open-circuit voltage of 4.94 V. This work establishes a new benchmark for multijunction PVs.

Reactive Plasma Deposition of ITO as an Efficient Buffer Layer for Inverted Perovskite Solar Cells

In this study, the potential of reactive plasma deposition (RPD) is demonstrated for fabricating indium tin oxide (ITO) as an efficient buffer layer in inverted wide-bandgap perovskite solar cells (PSCs). This method results in a certified efficiency of 21.33% for wide-bandgap PSCs, demonstrating superior thermal stability and operational stability. The optimized devices achieve an impressive open-circuit voltage (VOC) of 1.252 V with a bandgap of 1.67 eV, resulting in a remarkably low voltage deficit of 0.418 V, attributed to improved electron extraction, reduced interface defects, and suppressed surface recombination. The cells maintain over 90% of their initial efficiency after 1023 h of thermal aging at 88 °C. Furthermore, by integrating a highly efficient semi-transparent PSC with a CIGS bottom cell, a four-terminal tandem configuration is achieved with a total efficiency of 29.03%, representing one of the most efficient perovskite/CIGS tandem solar cells reported to date. This study provides valuable insights into the potential of RPD for improving the performance and scalability of inverted wide-bandgap PSCs.

Deep learning for augmented process monitoring of scalable perovskite thin-film fabrication

Reproducible large-area fabrication is one of the remaining challenges for the commercialization of perovskite photovoltaics. Imaging methods augmented with deep learning (DL) enable in-line detection of spatial or temporal inconsistencies and predict the impact of observed changes on device performance. In this work, we showcase three use cases of how DL augments complex experimental data analysis of the large-area perovskite thin film formation, even on moderate-sized datasets. First, we demonstrate material composition monitoring by differentiating between precursor property variations, ensuring material consistency during fabrication. Second, we provide early thin-film quality assessment by predicting holistic device performance even before its finalization. Finally, we extend the approach from parameter prediction to generating recommendations for process control by forecasting monitoring signals as a function of a variable process parameter and predicting the corresponding device performances. By addressing tasks that are hardly possible for humans to solve, we present how DL augments data analysis by transforming experimental data into predictions of target parameters.

Theoretical Insights into Ultrafast Separation of Photogenerated Charges in a Push-Pull Polarized Molecular Triad

Herein, we propose a purely-organic donor-acceptor (D-A) molecular triad, with a light-absorbing polarized molecular wire (PMW) used as a central linkage, as a proof of concept for the possible future applications of the D-PMW-A arrangement in molecular photovoltaics. This work builds upon our earlier study on the PMW unit itself, which proved to be highly promising for the ultrafast photogeneration of free charge carriers. Quantum-chemical calculations performed for the D-PMW-A triad at a semi-empirical level of theory reveal a large electric dipole moment of the system, and show strong charge-transfer (CT) character of its lowest-energy excited electronic states, including theS 1 ${S_1 }$ , which favours efficient dissociation of an exciton initially formed upon the absorption of light. The confirmation for this effect was found with nonadiabatic molecular dynamics simulations, revealing an ultrafast relaxation from higher, bright excited states toS 1 ${S_1 }$ , completed on a subpicosecond timescale. The architecture of the proposed molecular triad enables its electronic coupling to the surrounding environment through chemical bonds, or noncovalent stacking interactions, which might open way for synthesis of a new class of D-PMW-A efficient molecular organic photovoltaic materials.

25.91%-Efficiency and Durable Inverted Perovskite Solar Cells Enabled by a Multifunctional Molecule Mediated Precursor Engineering

The stability of the precursor is essential for producing high-quality perovskite films with minimal non-radiative recombination. In this study, methionine sulfoxide (MTSO), which features multiple electron-donation sites, is strategically chosen as a precursor stabilizer and crystal growth mediator for inverted perovskite solar cells (PSCs). MTSO stabilizes the precursor by inhibiting the oxidation of iodide ions and passivates charged traps through coordination and hydrogen bonding interactions. This leads to enhanced crystallinity, reduced non-radiative recombination, and decreased internal residual stress in perovskite film. As a result, remarkable power conversion efficiencies of 25.91% (certified 25.76%) with a minimal voltage deficit of 0.36 V for a 0.09-cm2 inverted PSC, and 21.96% for a 12.96-cm2 (active area) perovskite minimodule, have been achieved, respectively. Furthermore, the unencapsulated devices demonstrated excellent long-term thermal aging and operational stability, retaining over 90% and 92% of their original efficiencies after 500 h of continuous thermal aging at 85 °C and 2500 h of continuous maximum power point tracking under 1 sun (white light LED array) illumination at 30 ± 5 °C. This study underscores the importance of the rational design of functional molecules for stabilizing the precursor and regulating the crystallization of perovskite films, advancing the practical development of PSCs.

Interfacial Work Function Modulation of Wide Bandgap Perovskite Solar Cell for Efficient Perovskite/CIGS Tandem Solar Cell

Wide-bandgap perovskite solar cells (PVSCs), a promising top-cell candidate for high-performance tandem solar cells, often suffer from larger open-circuit voltage (VOC) deficits as the bandgap increases. Surface passivation is a common strategy to mitigate these VOC deficits. However, understanding the mechanisms underlying the differences in passivation effects among various types of molecules remains limited, which is crucial for developing universal interface passivation strategies and guiding the design of passivation molecules. This study compares the passivation effects of phenethylammonium iodide (PEAI) and piperazine iodine (PI) on VOC in wide-bandgap PVSCs with a 1.66 eV bandgap. Results show that PI significantly enhances VOC, whereas PEAI does not. This improvement is attributed to increased built-in voltage (Vbi) in PI-treated PVSCs, stemming from a lower work function, which enhances carrier selectivity at the contact interfaces. The champion power conversion efficiency of the PVSCs is 21.47%, with a VOC of 1.23 V and a VOC loss of 0.43 V. The strategy is also effective for PVSCs with bandgaps of 1.56 and 1.81 eV. By layering semi-transparent perovskite top cells onto copper indium gallium selenide (CIGS) bottom cells, a PCE of 26.36% is achieved in perovskite/CIGS 4-terminal tandem solar cells.

Nuclear Quadrupolar Resonance Structural Characterization of Halide Perovskites and Perovskitoids: A Roadmap from Electronic Structure Calculations for Lead-Iodide-Based Compounds

Metal halide perovskites, including some of their related perovskitoid structures, form a semiconductor class of their own, which is arousing ever-growing interest from the scientific community. With halides being involved in the various structural arrangements, namely, pure corner-sharing MX6 (M is metal and X is halide) octahedra, for perovskite networks, or alternatively a combination of corner-, edge-, and/or face-sharing for related perovskitoids, they represent the ideal probe for characterizing the way octahedra are linked together. Well known for their inherently large quadrupolar constants, which is detrimental to the resolution of nuclear magnetic resonance spectroscopy, most abundant halide isotopes (35/37Cl, 79/81Br, 127I) are in turn attractive for magnetic field-free nuclear quadrupolar resonance (NQR) spectroscopy. Here, we investigate the possibility of exploiting NQR spectroscopy of halides to distinctively characterize the various metal halide structural arrangements, using density functional theory simulations. Our calculations nicely match the available experimental results. Furthermore, they demonstrate that compounds with different connectivities of their MX6 building blocks, including lower dimensionalities such as 2D networks, show distinct NQR signals in a broad spectral window. They finally provide a roadmap of the characteristic NQR frequency ranges for each octahedral connectivity, which may be a useful guide to experimentalists, considering the long acquisition procedures typical of NQR. We hope this work will encourage the incorporation of NQR spectroscopy to further our knowledge of the structural diversity of metal halides.

A spiro-type self-assembled hole transporting monolayer for highly efficient and stable inverted perovskite solar cells and modules

Self-assembled monolayers (SAMs) have significantly contributed to the advancement of hole transporting materials (HTMs) for inverted perovskite solar cells (PSCs). However, uneven distribution of SAMs on the substrate largely decreases the PSC performance, especially for large-scale devices. Herein, the first spiro-type SAM, termed 4PA-spiro, with an orthogonal spiro[acridine-9,9'-fluorene] as the skeleton and phosphonic acid as the anchoring group were proposed. Compared to the reference 4PACz, the twisted configuration with larger steric hindrance of 4PA-spiro inhibited the intermolecular aggregation, enabling a uniform and homogeneous anchoring on the substrate. Moreover, the suitable highest occupied molecular orbital (HOMO) level of 4PA-spiro is beneficial in promoting hole extraction and reducing charge non-radiative recombination. As a result, compared to 4PACz with a power conversion efficiency (PCE) of 22.10%, the 4PA-spiro-based PSCs exhibited a superior PCE of 25.28% (certified 24.81%, 0.05 cm2), along with excellent long-term stability. More importantly, 4PA-spiro-enabled larger-area PSCs and modules achieved PCEs of 24.11% (1.0 cm2) and 21.89% (29.0 cm2), respectively, one of the highest PCEs for inverted PSC modules, providing an effective SAM candidate for the commercialization of efficient, stable and large-scale inverted PSCs.

A Stepwise Melting-Polymerizing Molecule for Hydrophobic Grain-Scale Encapsulated Perovskite Solar Cell

Despite the ongoing increase in the efficiency of perovskite solar cells, the stability issues of perovskite have been a significant hindrance to its commercialization. In response to this challenge, a stepwise melting-polymerizing molecule (SMPM) is designed as an additive into FAPbI3 perovskite. SMPM undergoes a three-stage phase transition during the perovskite annealing process: initially melting from solid to liquid state, followed by overflowing grain boundaries, and finally self-polymerizing to form a hydrophobic grain-scale encapsulation in perovskite solar cells, providing protection against humidity-induced degradation. With this unique property, coupled with the advantages of improved crystallization, diminished non-radiative recombination, and energy level alignment, FAPbI3-based perovskite solar cells with a 25.21% (small-area) and 22.94% (1 cm2) power conversion efficiency and over 2000 h T95% stability under 85% relative humidity is achieved. Furthermore, the SMPM-based perovskite solar cells without external encapsulations sustain impressive stability during underwater operation, in which the black FAPbI3 phase is maintained and Pb-leakage is also effectively suppressed. Therefore, the SMPM strategy can offer a sustainable settlement in both stability and environmental issues for the commercialization of perovskite solar cells.

Cost-Effective Synthesis Method: Toxic Solvent-Free Approach for Stable Mixed Cation Perovskite Powders in Photovoltaic Applications

Organometallic lead halide perovskite powders have gained widespread attention for their intriguing properties, showcasing remarkable performance in the optoelectronic applications. In this study, formamidinium lead iodide (α-FAPbI3) microcrystals (MCs) is synthesized using retrograde solubility-driven crystallization. Additionally, methylammonium lead bromide (MAPbBr3) and cesium lead iodide (δ-CsPbI3) MCs are prepared through a sonochemical process, employing low-grade PbX2 (X = I & Br) precursors and an eco-friendly green solvent (γ-Valerolactone). The study encompasses an analysis of the structural, optical, thermal, elemental, and morphological characteristics of FAPbI3, MAPbBr3, and CsPbI3 MCs. Upon analysing phase stability, a phase transition in FAPbI3 MCs is observed after 2 weeks. To address this issue, a powder-based mechanochemical method is employed to synthesize stable mixed cation perovskite powders (MCPs) by subjecting FAPbI3 and MAPbBr3 MCs with varying concentrations of CsPbI3. Furthermore, the performance of mixed cation perovskites are examined using the Solar Cell Capacitance Simulator (SCAPS-1D) software. The impact of cesium incorporation in the photovoltaic characteristics is elucidated. All mixed cation absorbers exhibited optimal device performance with a thickness ranging between 0.6-1.5 µm. It's worth noting that the MCPs exhibit impressive ambient stability, remaining structurally intact and retaining their properties without significant degradation for 70 days of ambient exposure.

Clarifying the degradation process of luminescent inorganic perovskite nanocrystals

Metal halide perovskites have emerged as highly promising materials for a range of optoelectronic applications. However, their sensitivity to environmental factors, particularly air moisture, presents significant challenges for both reliable research and commercialization. Moisture-induced degradation is a major issue due to the ionic nature of perovskites, which significantly impacts their luminescent properties. Despite extensive research efforts focusing on device applications, a comprehensive understanding of the degradation mechanisms in perovskites remains limited, largely due to their intrinsic ionic characteristics. In this work, we perform an in-depth analysis of the degradation process in perovskite nanocrystals (NCs) synthesized with varying reaction times, exploring the correlation between their optical and structural properties. Our findings reveal that perovskite NCs with larger crystal sizes exhibit greater stability in ambient air, attributed to their lower surface-to-volume ratio. These insights offer a deeper understanding of the relationship between perovskite NC degradation and their optical performance, contributing to advancements in the field of perovskite-based light-emitting technologies.

Polyoxometalate Reinforced Perovskite Phase for High-Performance Perovskite Photovoltaics

Ionic hybrid perovskites face challenges in maintaining their structural stability against non-equilibrium phase degradation, therefore, it is essential to develop effective ways to reinforce their corner-shared [PbI6]4- octahedral units. To strengthen structural stability, redox-active functional polyoxometalates (POMs) are developed and incorporated into perovskite solar cells (PSCs) to form a robust polyoxometalates/perovskite interlayer for stabilizing the perovskite phase. This approach offers several advantages: 1) promotes the formation of an interfacial connecting layer to passivate interfacial defects in addition to stabilize the [PbI6]4- units through exchanged ammonium cations in POMs with perovskites; 2) facilitates continuous structural repairing of Pb0- and I0-rich defects in the [PbI6]4- unit through redox electron shuttling of the electroactive metal ions in POMs; 3) provides guidance for selecting suitable redox mediators based on the kinetic studies of POM's effectiveness in reacting with targeted defects. The POM-reinforced device maintains 97.2% of its initial PCE after 1500 h of shelf-life test at 65 °C, while also enhancing the long-term operational stability. Additionally, this approach can be generally applicable across scalable sizes and various bandgap perovskites in devices, showing the promise of using functional POMs to enhance perovskite photovoltaic performance.

Perovskite/silicon tandem solar cells with bilayer interface passivation

Two-terminal monolithic perovskite/silicon tandem solar cells demonstrate huge advantages in power conversion efficiency compared with their respective single-junction counterparts1,2. However, suppressing interfacial recombination at the wide-bandgap perovskite/electron transport layer interface, without compromising its superior charge transport performance, remains a substantial challenge for perovskite/silicon tandem cells3,4. By exploiting the nanoscale discretely distributed lithium fluoride ultrathin layer followed by an additional deposition of diammonium diiodide molecule, we have devised a bilayer-intertwined passivation strategy that combines efficient electron extraction with further suppression of non-radiative recombination. We constructed perovskite/silicon tandem devices on a double-textured Czochralski-based silicon heterojunction cell, which featured a mildly textured front surface and a heavily textured rear surface, leading to simultaneously enhanced photocurrent and uncompromised rear passivation. The resulting perovskite/silicon tandem achieved an independently certified stabilized power conversion efficiency of 33.89%, accompanied by an impressive fill factor of 83.0% and an open-circuit voltage of nearly 1.97 V. To the best of our knowledge, this represents the first reported certified efficiency of a two-junction tandem solar cell exceeding the single-junction Shockley-Queisser limit of 33.7%.

Molecular Orientation Regulation of Hole Transport Semicrystalline-Polymer Enables High-Performance Carbon-Electrode Perovskite Solar Cells

Carbon-based perovskite solar cells (PSCs) coupled with solution-processed hole transport layers (HTLs) have shown potential owing to their combination of low cost and high performance. However, the commonly used poly(3-hexylthiophene) (P3HT) semicrystalline-polymer HTL dominantly shows edge-on molecular orientation, in which the alkyl side chains directly contact the perovskite layer, resulting in an electronically poor contact at the perovskite/P3HT interface. The study adopts a synergetic strategy comprising of additive and solvent engineering to transfer the edge-on molecular orientation of P3HT HTL into 3D molecular orientation. The target P3HT HTL possesses improved charge transport as well as enhanced moisture-repelling capability. Moreover, energy level alignment between target P3HT HTL and perovskite layer is realized. As a result, the champion devices with small (0.04 cm2) and larger areas (1 cm2) deliver notable efficiencies of 20.55% and 18.32%, respectively, which are among the highest efficiency of carbon-electrode PSCs.

Alder-Ene Reaction-Mediated Suppression of Tin(II) Oxidation for Efficient Tin-Lead Perovskite Solar Cells

Despite numerous studies have reported the inhibition of tin (II) oxidation in mixed tin-lead halide perovskite, there remains a dearth of mechanistic information regarding how tin (II) undergoes oxidation in the precursor solution, particularly in terms of the involvement of DMSO. We here take advantage of density functional theory (DFT) to uncover that SnI2 can coordinate with DMSO and react with singlet oxygen, resulting in the generation of Sn (IV). Moreover, our DFT simulations reveal that benzaldehyde oxime (BZHO) competes with SnI2 in reacting with oxygen through the Alder-ene reaction, hence effectively restraining the oxidation of tin (II), which is further verified by several experimental characterizations. Besides, the introduction of BZHO has also regulated the crystallization of the perovskite film and modified the electronic structure of the perovskite surface. As a result, the perovskite solar cells with the addition of BZHO demonstrate superior performance and operational stability, retaining 82 % of the initial PCE under continuous 1-sun illumination for 800 hours. Furthermore, the efficiency of all-perovskite tandem solar cells treated with BZHO reached 26.76 %. Therefore, this work presents a promising strategy for designing high-performance and stable all-perovskite tandem solar cells.

Imaging hot photocarrier transfer across a semiconductor heterojunction with ultrafast electron microscopy

Semiconductor heterojunctions have gained significant attention for efficient optoelectronic devices owing to their unique interfaces and synergistic effects. Interaction between charge carriers with the heterojunction plays a crucial role in determining device performance, while its spatial-temporal mapping remains lacking. In this study, we employ scanning ultrafast electron microscopy (SUEM), an emerging technique that combines high spatial-temporal resolution and surface sensitivity, to investigate photocarrier dynamics across a Si/Ge heterojunction. Charge dynamics are selectively examined across the junction and compared to far bulk areas, through which the impact of the built-in potential, band offsets, and surface effects is directly visualized. In particular, we find that the heterojunction drastically modifies the hot photocarrier diffusivities in both Si and Ge regions due to charge trapping. These findings are further elucidated with insights from the band structure and surface potential measured by complementary techniques. This work demonstrates the tremendous effect of heterointerfaces on hot photocarrier dynamics and showcases the potential of SUEM in characterizing realistic optoelectronic devices.

Molecular dynamics simulation for phase transition of CsPbI3 perovskite with the Buckingham potential

The CsPbI3 perovskite is a promising candidate for photovoltaic applications, for which several critical phase transitions govern both its efficiency and stability. Large-scale molecular dynamics simulations are valuable in understanding the microscopic mechanisms of these transitions, in which the accuracy of the simulation heavily depends on the empirical potential. This study parameterizes two efficient and stable empirical potentials for the CsPbI3 perovskite. In these two empirical potentials, the short-ranged repulsive interaction is described by the Lennard-Jones model or the Buckingham model, while the long-ranged Coulomb interaction is summed by the damped shifted force method. Our molecular dynamics simulations show that these two empirical potentials accurately capture the γ ↔ β ↔ α and δ → α phase transitions for the CsPbI3 perovskite. Furthermore, they are up to two orders of magnitude more efficient than previous empirical models, owing to the high efficiency of the damped shifted force truncation treatment for the Coulomb interaction.

Surface Molecular Engineering for Fully Textured Perovskite/Silicon Tandem Solar Cells

Developing large-scale monolithic perovskite/silicon tandem devices based on industrial Czochralski silicon wafers will likely have to adopt double-side textured architecture, given their optical benefits and low manufacturing costs. However, the surface engineering strategies that are widely used in solution-processed perovskites to regulate the interface properties are not directly applicable to micrometric textures. Here, we devise a surface passivation strategy by dynamic spray coating (DSC) fluorinated thiophenethylammonium ligands, combining the advantages of providing conformal coverage and suppressing phase conversion on textured surfaces. From the viewpoint of molecular engineering, theoretical calculation and experimental results demonstrate that introducing trifluoromethyl group provide more effective surface passivation through strong interaction and energy alignment by forming a dipole layer. Consequently, the DSC treatment of this bifunctional molecule enables the tandem cells based on industrial silicon wafers to achieve a certified stabilized power conversion efficiency of 30.89 %. In addition, encapsulated devices display excellent operational stability by retaining over 97 % of their initial performance after 600 h continuous illumination.

Suppressed Ion Migration by Heterojunction Layer for Stable Wide-Bandgap Perovskite and Tandem Photovoltaics

Wide-bandgap (WBG) perovskite has demonstrated great potential in perovskite-based tandem solar cells. The power conversion efficiency (PCE) of such devices has surpassed 34%, signifying a new era for renewable energy development. However, the ion migration reduces the stability and hinders the commercialization, which is yet to be resolved despite many attempts. A big step forward has now been achieved by the simulation method. The detailed thermodynamics and kinetics of the migration process have been revealed for the first time. The stability has been enhanced by more than 100% via the heterojunction layer on top of the WBG perovskite film, which provided extra bonding for kinetic protection. Hopefully, these discoveries will open a new gate for WBG perovskite research and accelerate the application of perovskite-based tandem solar cells.

Crown Ethers with Different Cavity Diameters Inhibit Ion Migration and Passivate Defects toward Efficient and Stable Lead Halide Perovskite Solar Cells

Organic-inorganic hybrid metal halide perovskite solar cells have been considered as one of the most promising next-generation photovoltaic technologies. Nevertheless, perovskite defects and Li+ ionic migration will seriously affect the power conversion efficiency and stability of the formal device. Herein, we designed two crown ether derivatives (PC12 and PC15) with different cavity diameters, which selectively bind to different metal cations. It is found that PC15 in perovskite precursor solution can actively regulate the nucleation and crystallization processes and passivate the uncoordinated Pb2+ ions, while PC12 at the interface between the perovskite layer and hole-transporting layer can effectively inhibit the migration of Li+ ions and reduce nonradiative recombination losses. Therefore, PC12 and PC15 can act as "lubricant" and defect passivators, as well as inhibitors of ion migration, when they are synergistically applied at the surface and bulk of perovskite layer. Consequently, the optimized device achieved a champion efficiency of 24.8% with significantly improved humidity, thermal, and light stability.

Assembling the 2D-3D-2D Heterostructure of Quasi-2D Perovskites for High-Performance Solar Cells

Quasi-two-dimensional (quasi-2D) layered perovskites with mixed dimensions offer a promising avenue for stable and efficient solar cells. However, randomly distributed three-dimensional (3D) perovskites near the film surface limit the device performance of quasi-2D perovskites due to increased nonradiative recombination and ion migration. Herein, we construct a 2D (n = 4 top)-3D-2D (n = 2 bottom) heterostructure of quasi-2D perovskites by using 3-chlorobenzylamine iodine, which can effectively reduce defect density and restrain ion migration. A champion efficiency of 22.22% for quasi-2D perovskite solar cells is achieved due to remarkably reduced nonradiative voltage loss and increased electron extraction. Additionally, the 2D-3D-2D perovskite solar cells also exhibit excellent thermal and humidity stabilities, retaining over 90 and 85% of the initial efficiencies after 2000 h under a heat stress of 65 °C and at air ambient of ∼50% humidity, respectively. Our results provide a general approach to tune perovskite films for suppressing ion migration and achieving high-performance perovskite solar cells.

Structural Decoration of Porphyrin/Phthalocyanine Photovoltaic Materials

Porphyrin/phthalocyanine compounds with fascinating molecular structures have attracted widespread attention in the field of solar cells in recent years. In this review, we focus on the pivotal role of porphyrin and phthalocyanine compounds in enhancing the efficiency of solar cells. The review seamlessly integrates the intricate molecular structures of porphyrins and phthalocyanines with their proficiency in absorbing visible light and facilitating electron transfer, key processes in converting sunlight into electricity. By delving into the nuances of intramolecular regulation, aggregated states, and surface/interface structure manipulation, it elucidates how various levels of molecular modifications enhance solar cell efficiency through improved charge transfer, stability, and overall performance. This comprehensive exploration provides a detailed understanding of the complex relationship between molecular design and solar cell performance, discussing current advancements and potential future applications of these molecules in solar energy technology.

Large-Area Perovskite Solar Module Produced by Introducing Self-Assembled L-Histidine Monolayer at TiO2 and Perovskite Interface

Perovskite solar cells have been proven to enhance cell characteristics by introducing passivation materials that suppress defect formation. Defect states between the electron transport layer and the absorption layer reduce electron extraction and carrier transport capabilities, leading to a significant decline in device performance and stability, as well as an increased probability of non-radiative recombination. This study proposes the use of an amino acid (L-Histidine) self-assembled monolayer material between the transport layer and the perovskite absorption layer. Surface analysis revealed that the introduction of L-Histidine improved both the uniformity and roughness of the perovskite film surface. X-ray photoelectron spectroscopic analysis showed a reduction in oxygen vacancies in the lattice and an increase in Ti4+, indicating that L-Histidine successfully passivated trap states at the perovskite and TiO2 electron transport layer interface. In terms of device performance, the introduction of L-Histidine significantly improved the fill factor (FF) because the reduction in interface defects could suppress charge accumulation and reduce device hysteresis. The FF of large-area solar modules (25 cm2) with L-Histidine increased from 55% to 73%, and the power conversion efficiency (PCE) reached 16.5%. After 500 h of aging tests, the PCE still maintained 91% of its original efficiency. This study demonstrates the significant impact of L-Histidine on transport properties and showcases its potential for application in the development of large-area perovskite module processes.

Enhanced cation interaction in perovskites for efficient tandem solar cells with silicon

To achieve the full potential of monolithic perovskite/silicon tandem solar cells, crystal defects and film inhomogeneities in the perovskite top cell must be minimized. We discuss the use of methylenediammonium dichloride as an additive to the perovskite precursor solution, resulting in the incorporation of in situ-formed tetrahydrotriazinium (THTZ-H+) into the perovskite lattice upon film crystallization. The cyclic nature of the THTZ-H+ cation enables a strong interaction with the lead octahedra of the perovskite lattice through the formation of hydrogen bonds with iodide in multiple directions. This structure improves the device power conversion efficiency (PCE) and phase stability of 1.68 electron volts perovskites under prolonged light and heat exposure under 1-sun illumination at 85°C. Monolithic perovskite/silicon tandems incorporating THTZ-H+ in the perovskite photo absorber reached a 33.7% independently certified PCE for a device area of 1 square centimeter.

Ligand Homogenized Br-I Wide-Bandgap Perovskites for Efficient NiOx-Based Inverted Semitransparent and Tandem Solar Cells

Phase heterogeneity of bromine-iodine (Br-I) mixed wide-bandgap (WBG) perovskites has detrimental effects on solar cell performance and stability. Here, we report a heterointerface anchoring strategy to homogenize the Br-I distribution and mitigate the segregation of Br-rich WBG-perovskite phases. We find that methoxy-substituted phenyl ethylammonium (x-MeOPEA+) ligands not only contribute to the crystal growth with vertical orientation but also promote halide homogenization and defect passivation near the buried perovskite/hole transport layer (HTL) interface as well as reduce trap-mediated recombination. Based on improvements in WBG-perovskite homogeneity and heterointerface contacts, NiOx-based opaque WBG-perovskite solar cells (WBG-PSCs) achieved impressive open-circuit voltage (Voc) and fill factor (FF) values of 1.22 V and 83%, respectively. Moreover, semitransparent WBG-PSCs exhibit a PCE of 18.5% (15.4% for the IZO front side) and a high FF of 80.7% (79.4% for the IZO front side) for a designated illumination area (da) of 0.12 cm2. Such a strategy further enables 24.3%-efficient two-terminal perovskite/silicon (double-polished) tandem solar cells (da of 1.159 cm2) with a high Voc of over 1.90 V. The tandem devices also show high operational stability over 1000 h during T90 lifetime measurements.

Solvent engineering for scalable fabrication of perovskite/silicon tandem solar cells in air

Perovskite/silicon tandem solar cells hold great promise for realizing high power conversion efficiency at low cost. However, achieving scalable fabrication of wide-bandgap perovskite (~1.68 eV) in air, without the protective environment of an inert atmosphere, remains challenging due to moisture-induced degradation of perovskite films. Herein, this study reveals that the extent of moisture interference is significantly influenced by the properties of solvent. We further demonstrate that n-Butanol (nBA), with its low polarity and moderate volatilization rate, not only mitigates the detrimental effects of moisture in air during scalable fabrication but also enhances the uniformity of perovskite films. This approach enables us to achieve an impressive efficiency of 29.4% (certified 28.7%) for double-sided textured perovskite/silicon tandem cells featuring large-size pyramids (2-3 μm) and 26.3% over an aperture area of 16 cm2. This advance provides a route for large-scale production of perovskite/silicon tandem solar cells, marking a significant stride toward their commercial viability.

The dawn of MXene duo: revolutionizing perovskite solar cells with MXenes through computational and experimental methods

Integrating MXene into perovskite solar cells (PSCs) has heralded a new era of efficient and stable photovoltaic devices owing to their supreme electrical conductivity, excellent carrier mobility, adjustable surface functional groups, excellent transparency and superior mechanical properties. This review provides a comprehensive overview of the experimental and computational techniques employed in the synthesis, characterization, coating techniques and performance optimization of MXene additive in electrodes, hole transport layer (HTL), electron transport layer (ETL) and perovskite photoactive layer of the perovskite solar cells (PSCs). Experimentally, the synthesis of MXene involves various methods, such as selective etching of MAX phases and subsequent delamination. At the same time, characterization techniques encompass X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, which elucidate the structural and chemical properties of MXene. Experimental strategies for fabricating PSCs involving MXene include interfacial engineering, charge transport enhancement, and stability improvement. On the computational front, density functional theory calculations, drift-diffusion modelling, and finite element analysis are utilized to understand MXene's electronic structure, its interface with perovskite, and the transport mechanisms within the devices. This review serves as a roadmap for researchers to leverage a diverse array of experimental and computational methods in harnessing the potential of MXene for advanced PSCs.

Band gap tuning of perovskite solar cells for enhancing the efficiency and stability: issues and prospects

The intriguing optoelectronic properties, diverse applications, and facile fabrication techniques of perovskite materials have garnered substantial research interest worldwide. Their outstanding performance in solar cell applications and excellent efficiency at the lab scale have already been proven. However, owing to their low stability, the widespread manufacturing of perovskite solar cells (PSCs) for commercialization is still far off. Several instability factors of PSCs, including the intrinsic and extrinsic instability of perovskite materials, have already been identified, and a variety of approaches have been adopted to improve the material quality, stability, and efficiency of PSCs. In this review, we have comprehensively presented the significance of band gap tuning in achieving both high-performance and high-stability PSCs in the presence of various degradation factors. By investigating the mechanisms of band gap engineering, we have highlighted its pivotal role in optimizing PSCs for improved efficiency and resilience.

Key Roles of Interfaces in Inverted Metal-Halide Perovskite Solar Cells

Metal-halide perovskite solar cells (PSCs), an emerging technology for transforming solar energy into a clean source of electricity, have reached efficiency levels comparable to those of commercial silicon cells. Compared with other types of PSCs, inverted perovskite solar cells (IPSCs) have shown promise with regard to commercialization due to their facile fabrication and excellent optoelectronic properties. The interlayer interfaces play an important role in the performance of perovskite cells, not only affecting charge transfer and transport, but also acting as a barrier against oxygen and moisture permeation. Herein, we describe and summarize the last three years of studies that summarize the advantages of interface engineering-based advances for the commercialization of IPSCs. This review includes a brief introduction of the structure and working principle of IPSCs, and analyzes how interfaces affect the performance of IPSC devices from the perspective of photovoltaic performance and device lifetime. In addition, a comprehensive summary of various interface engineering approaches to solving these problems and challenges in IPSCs, including the use of interlayers, interface modification, defect passivation, and others, is summarized. Moreover, based upon current developments and breakthroughs, fundamental and engineering perspectives on future commercialization pathways are provided for the innovation and design of next-generation IPSCs.

Research Progress on Rashba Effect in Two-Dimensional Organic-Inorganic Hybrid Lead Halide Perovskites

The Rashba effect appears in the semiconductors with an inversion-asymmetric structure and strong spin-orbit coupling, which splits the spin-degenerated band into two sub-bands with opposite spin states. The Rashba effect can not only be used to regulate carrier relaxations, thereby improving the performance of photoelectric devices, but also used to expand the applications of semiconductors in spintronics. In this mini-review, recent research progress on the Rashba effect of two-dimensional (2D) organic-inorganic hybrid perovskites is summarized. The origin and magnitude of Rashba spin splitting, layer-dependent Rashba band splitting of 2D perovskites, the Rashba effect in 2D perovskite quantum dots, a 2D/3D perovskite composite, and 2D-perovskites-based van der Waals heterostructures are discussed. Moreover, applications of the 2D Rashba effect in circularly polarized light detection are reviewed. Finally, future research to modulate the Rashba strength in 2D perovskites is prospected, which is conceived to promote the optoelectronic and spintronic applications of 2D perovskites.

Emerging Nonlinear Photocurrents in Lead Halide Perovskites for Spintronics

Lead halide perovskites (LHPs) containing organic parts are emerging optoelectronic materials with a wide range of applications thanks to their high optical absorption, carrier mobility, and easy preparation methods. They possess spin-dependent properties, such as strong spin-orbit coupling (SOC), and are promising for spintronics. The Rashba effect in LHPs can be manipulated by a magnetic field and a polarized light field. Considering the surfaces and interfaces of LHPs, light polarization-dependent optoelectronics of LHPs has attracted attention, especially in terms of spin-dependent photocurrents (SDPs). Currently, there are intense efforts being made in the identification and separation of SDPs and spin-to-charge interconversion in LHP. Here, we provide a comprehensive review of second-order nonlinear photocurrents in LHP in regard to spintronics. First, a detailed background on Rashba SOC and its related effects (including the inverse Rashba-Edelstein effect) is given. Subsequently, nonlinear photo-induced effects leading to SDPs are presented. Then, SDPs due to the photo-induced inverse spin Hall effect and the circular photogalvanic effect, together with photocurrent due to the photon drag effect, are compared. This is followed by the main focus of nonlinear photocurrents in LHPs containing organic parts, starting from fundamentals related to spin-dependent optoelectronics. Finally, we conclude with a brief summary and future prospects.

Sublimed C60 for efficient and repeatable perovskite-based solar cells

Thermally evaporated C60 is a near-ubiquitous electron transport layer in state-of-the-art p-i-n perovskite-based solar cells. As perovskite photovoltaic technologies are moving toward industrialization, batch-to-batch reproducibility of device performances becomes crucial. Here, we show that commercial as-received (99.75% pure) C60 source materials may coalesce during repeated thermal evaporation processes, jeopardizing such reproducibility. We find that the coalescence is due to oxygen present in the initial source powder and leads to the formation of deep states within the perovskite bandgap, resulting in a systematic decrease in solar cell performance. However, further purification (through sublimation) of the C60 to 99.95% before evaporation is found to hinder coalescence, with the associated solar cell performances being fully reproducible after repeated processing. We verify the universality of this behavior on perovskite/silicon tandem solar cells by demonstrating their open-circuit voltages and fill factors to remain at 1950 mV and 81% respectively, over eight repeated processes using the same sublimed C60 source material. Notably, one of these cells achieved a certified power conversion efficiency of 30.9%. These findings provide insights crucial for the advancement of perovskite photovoltaic technologies towards scaled production with high process yield.