Fully Textured, Production-Line Compatible Monolithic Perovskite/Silicon Tandem Solar Cells Approaching 29% Efficiency

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.

Modification at ITO/NiOx Interface with MoS2 Enables Hole Transport for Efficient and Stable Inverted Perovskite Solar Cells

Inverted perovskite solar cells (IPSCs) utilizing nickel oxide (NiOx) as hole transport material have made great progress, driven by improvements in materials and interface engineering. However, challenges remain due to the low intrinsic conductivity of NiOx and inefficient hole transport. In this study, we introduced MoS2 nanoparticles at the indium tin oxide (ITO) /NiOx interface to enhance the ITO surface and optimize the deposition of NiOx, resulting in increased conductivity linked to a ratio of Ni3+:Ni2+. This interface modification not only optimized energy level but also promoted hole transport and reduced defects. Consequently, IPSCs with MoS2 modified at ITO/NiOx interface achieved a champion power conversion efficiency (PCE) of 21.42 %, compared to 20.25 % without modification. Additionally, unencapsulated IPSCs with this interface modification displayed improved stability under thermal, light, humidity and ambient conditions. This innovative strategy for ITO/NiOx interface modification efficiently promotes hole transportation and can be integrated with other interface engineering approaches, offering valuable insights for the development of highly efficient and stable IPSCs.

Dimensional Control in Phase-Pure Coevaporated Quasi-2D Ruddlesden-Popper Structures

Fast, uncontrolled crystallization with several competing pathways makes solution-processing of phase-pure quasi-two-dimensional (quasi-2D) metal halide Ruddlesden-Popper thin films challenging. Typically, solution-processing results in the formation of different structural phases with varying dimensionality ranging from 2D, to quasi-2D, and 3D, introducing bandgap disorder and inhibiting charge transport. In this work, we eliminate interactions between precursor salts and solvents by using controlled thermal coevaporation to grow quasi-2D thin films that show high phase purity and narrow phase distribution. We study the structural landscape using synchrotron-based X-ray scattering and charge-carrier dynamics using ultrafast pump-probe spectroscopy. We then demonstrate a strategy to control the crystallographic phase of the film through phosphonic acid-based surface modification. We use density functional theory to study the interactions between propylphosphonic acid and the organic precursors and find that the interactions of loosely bound phosphonic acid molecules with evaporated precursors, followed by the migration of phosphonic acids through the deposited thin film, dictate the film structure between 2D and quasi-2D phases. These findings introduce new solvent-free methods for the fabrication of phase-pure quasi-2D Ruddlesden-Popper thin films and control phase selectivity across different dimensional (2D and quasi-2D) structures.

A Novel Self-Assembled Hole-Transporting Monolayer with Extending Conjugation for Inverted Perovskite Solar Cells

The application of self-assembled monolayers (SAMs) as hole-transporting materials has greatly improved the performance of inverted perovskite solar cells. Structure engineering of SAMs has proven to be an effective approach to enhance device performance. In this work, a novel SAM featuring extended conjugation is designed and synthesized, designated E-CbzBT. Compared with CbzBT, E-CbzBT exhibits enhanced asymmetric and noncoplanar screw-shaped configuration, leading to uniform and tight packing on ITO. The uniform packing of E-CbzBT increases the wettability of the perovskite precursor solution on the substrate, thereby facilitating perovskite crystallinity and suppressing interfacial trap density more effectively than CbzBT. Accordingly, inverted PSCs employing E-CbzBT reach a champion power conversion efficiency of 25.15%, surpassing 24.06% for CbzBT-based devices. Importantly, the E-CbzBT-based PSCs demonstrate superior ambient and thermal stability. The extending conjugation approach in SAMs represents a promising avenue for further advancements in perovskite solar cell technology.

Modulating Binding Strength and Acidity of Benzene-Derivative Ligands Enables Efficient and Hysteresis-Free Perovskite/Silicon Tandem Solar Cells

Passivating defects at the wide-bandgap perovskite/C60 interface without impeding interfacial charge transport can effectively enhance the efficiency of perovskite/silicon tandem solar cells (TSCs). Herein, we study the impact of benzene-derivative ligands with elaborately modulated binding strength and acidity on wide-bandgap perovskites for high-performance perovskite/silicon TSCs. Specifically, the acidity/alkalinity and binding strength are preliminarily tuned using different functional groups of -PO₃H₂, -COOH, and -NH₂, and further finely adjusted by altering the chain lengths between the benzene ring and the functional groups. The results show that strong binding is indispensable for effectively suppressing voltage loss. However, the commonly used benzylphosphonic acid (BPPA) for firm surface binding exhibits too strong acidity that can etch the perovskite surface, resulting in halide-vacancy defects and pronounced hysteresis. Increasing the side chain length of BPPA to (2-phenylethyl)phosphonic acid not only enables a suitable acid dissociation constant (pKa) to avoid acid-induced etching but also achieves robust anchoring to the perovskite surface with a parallel adsorption orientation, which reduces the charge transport barrier at the interface. These properties enable strong-adsorption surface termination (SAST) of the perovskite surface while preventing acid-induced etching. As a result, the SAST strategy achieves a remarkable efficiency of 32.13% (certified 31.72%) for hysteresis-free perovskite/silicon TSCs.

Colloidal Self-Assembly of CuCrO2 Nanocrystals for Durable Inverted Perovskite Solar Cells

Despite the promise of self-assembled organic hole-transport layers (HTLs) in inverted perovskite solar cells, critical concerns persist about their structural stability under external fields such as bias and illumination, which have been regarded as a potential threat to the device's longevity. To address this issue, instead of using self-assembled organic molecules, the intrinsically stable p-type, wide bandgap CuCrO2 colloidal nanocrystals with high monodispersity are synthesized and self-assembled them into HTL via a simple dip-coating method. By further HCl-mediated ligands exchange, the self-assembled CuCrO2-HTL creates a thermally stable chlorinated surface that can not only enhance the electronic coupling of inter nanocrystals but also provide contact passivation on the perovskite surface defects. These merits eventually endow the constructed buried interface with favorable contact, thus facilitating efficient and stable hole transfer. Consequently, an impressive power conversion efficiency of 25.35% is achieved, accompanied by greatly improved longevity under different accelerated-aging tests.

A Triphenylamine-Functionalized Co-Assembly Material for Record Efficiency Inverted CsPbI3 Perovskite Solar Cells

The precise regulation of self-assembled monolayer (SAM) distribution and interfacial modification is pivotal for advancing the performance of p-i-n inverted perovskite solar cells (PSCs). Here, a new co-assembly material, 4-(aminomethyl)-N,N-diphenylaniline iodide (TPAI), is developed to make SAM orderly assembled. Density functional theory (DFT) calculation and sum frequency generation (SFG) spectroscopy reveal that TPAI binds with SAM via π-π interactions, effectively suppressing SAM aggregation and enhancing the orderliness of self-assembly. Further characterization by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) demonstrates that ─NH3 group in TPAI coordinates with undercoordinated Pb2+ to passivate defects of cesium lead triiodide (CsPbI3) film. The TPAI modification creates a defect-minimized buried interface with optimized energy alignment, significantly improving hole extraction and transport kinetics. Consequently, the TPAI-treated CsPbI3 PSCs achieve a high power conversion efficiency (PCE) of 21.60%, the highest reported value for inverted CsPbI3 PSCs, maintaining 96.71% initial PCE after tracking at maximum power point (MPP) for 1400 h. This work provides a molecular-level strategy for interfacial engineering, advancing the development of efficient and durable perovskite photovoltaics.

Improving the Stability of Wide Bandgap Perovskites: Mechanisms, Strategies, and Applications in Tandem Solar Cells

Tandem solar cells (TSCs) based on wide bandgap (WBG) perovskites have gained significant attention for their higher power conversion efficiency (PCE) compared to single-junction cells. The role of WBG perovskite solar cells (PSCs) as the sub-cell in tandem cells consists of absorbing high-energy photons and producing higher open-circuit voltages (VOC). However, WBG PSCs face serious phase separation issues, resulting in poor long-term stability and substantial VOC loss in TSCs. In response, researchers have developed a range of strategies to mitigate these challenges, showing promising progress, and a comprehensive review of these strategies is expected. In this review, we discuss the stability mechanism in organic-inorganic hybrids and all-inorganic WBG perovskites. Additionally, we conduct an in-depth investigation of various strategies to enhance stability, including component engineering, additive engineering, interface engineering, dimension control, solvent engineering, and encapsulation. Furthermore, the application of the WBG sub-cell in various TSCs is summarized in detail. Finally, perspectives are provided to offer guidance for the development of efficient and stable WBG sub-cell in the field of TSCs.

Double Hole Transport Layers Enable 20.42% Efficiency Organic Solar Cells by Aggregation Control of Self-Assembled Molecules on Cobalt Salt Surfaces

Heterojunction interfaces play a crucial role in charge carrier transport, influencing the overall photovoltaic performance of organic solar cells (OSCs). Despite the importance, advancements in interfacial engineering, especially in optimizing the microstructure and nanomorphology, have not kept pace with research on photoactive layers. In the study, a strategy is explored to control the self-assembly growth of alcohol-soluble Me-4PACz (4P) used as a hole transport layer (HTL) in OSCs. The surface architecture is modified of inorganic Co salts via Cu doping and UV-ozone treatments, creating a smooth top surface with an increased Co3+/Co2+ ratio and hydroxyl groups. This meticulous design fine-tuned the assembly behavior of self-assembled molecules, resulting in the transition from spherical aggregates to a more uniform worm-like morphology. Additionally, the electrical and optical properties are optimized to passivate surface defects and enhance the wettability of organic solvents, leading to improved hole extraction and reduced interfacial charge carrier recombination losses. Consequently, an OSC with Cu-Co/4P as the HTL exhibited the highest power conversion efficiency of 20.42% (certified 20.20%). The characteristic universality and stability make the Cu-Co/4P HTL a potential candidate for widespread applications, particularly in providing rationalized guidance to further enhance the performance of OSCs.

Controlled Nucleation and Targeted Interface Modification in Wide-Bandgap Perovskite Solar Cells Based on Evaporation/Solution Two-Step Deposition

Solution deposition struggles to achieve conformal and pinhole-free wide-bandgap (WBG) perovskite films on micrometer-scale textured silicon subcells due to challenges in nucleation dynamics and film uniformity, necessitating smaller textures in the efficient perovskite/silicon tandems, which compromise light trapping and current density. While evaporation-assisted two-step deposition improves conformality, it often yields films with suboptimal crystallinity and a high defect density. To address this, we elucidate the formation mechanism of CsPbIxBr3-x nanocrystals during the thermal evaporation of PbI2/CsBr templates, which can serve as preferential nucleation sites to facilitate the growth of high-quality perovskite films. By optimizing evaporation conditions and incorporating 2,3,4,5,6-pentafluorobenzylphosphonic acid (pFBPA) during the spin-coating process, we achieved enhanced crystallization kinetics of nucleation sites and improved perovskite film uniformity. Further interface modification with pFBPA and ethane-1,2-diammonium iodide induces targeted surface dipoles at both carrier transport layers/perovskite interfaces, which not only offers better band alignment and surface passivation at both interfaces but also creates an enhanced electric field to boost electron extraction. These advancements enabled a WBG (1.68 eV) perovskite solar cell (PSC) to achieve an impressive power conversion efficiency (PCE) among WBG (1.65-1.7 eV) PSCs based on evaporation-assisted deposition. This study provides fundamental insights into achieving conformal high-quality WBG perovskite films, offering a theoretical foundation for the development of efficient perovskite/silicon tandems.

Recent Advances in Wide-Bandgap Perovskite Solar Cells

Wide-bandgap (WBG) perovskite solar cells (PSCs) have garnered considerable attention of late for their potential as semitransparent photovoltaics for building integration, top-cells in tandem configurations, and indoor photovoltaics (IPVs) for Internet of Things (IoT) applications. However, recent investigations have unveiled that underlying defect-mediated phase segregation, ion migration, lattice strain, and other factors can give rise to self-accelerated degradation reactions and the contraction of quasi-Fermi level splitting (QFLS) within devices. Extensive efforts have been undertaken to reduce defect densities in bulks, at surfaces, and across interfaces with charge transport layers (CTLs). This review provides a timely and comprehensive understanding of the intrinsic defect ecosystem in WBG perovskites, and mechanistically elucidates their impacts on device stability and open circuit voltage losses. Subsequently, recent advances in defect passivation strategies are cross-sectionally overviewed, covering various components of devices. The applications of WBG PSCs in semitransparent devices, tandem applications, and IPVs are discussed. Finally, prospects and challenges are proposed, providing insights for future research and technological advancements.

Enhanced Buried Interface Engineering for Efficient Inverted Perovskite Solar Cells Fabricated via Vapor-Solid Reaction

Vapor-deposited inverted perovskite solar cells utilizing self-assembled monolayer (SAM) as hole transport material have gained significant attention for their high efficiencies and compatibility with silicon/perovskite monolithic tandem devices. However, as a small molecule, the SAM layer suffers low thermal tolerance in comparison with other metal oxide or polymers, rendering poor efficiency in solar device with high-temperature (> 160 °C) fabricating procedures. In this study, a dual modification approach involving AlOx and F-doped phenyltrimethylammonium bromide (F-PTABr) layers is introduced to enhance the buried interface. The AlOx dielectric layer improves the interface contact and prevents the upward diffusion of SAM molecules during the vapor-solid reaction at 170 °C, while the F-PTABr layer regulates crystal growth and reduces the interfacial defects. As a result, the AlOx/F-PTABr-treated perovskite film exhibits a homogeneous, pinhole-free morphology with improved crystal quality compared to the control films. This leads to a champion power conversion efficiency of 21.53% for the inverted perovskite solar cells. Moreover, the encapsulated devices maintained 90% of the initial efficiency after 600 h of ageing at 85 °C in air, demonstrating promising potential for silicon/perovskite tandem application.

Restrain Phase Segregation by In Situ Buried Prenucleation for Efficient and Stable Wide-Band Gap Perovskite Cells

The phase segregation of wide-band gap perovskite solar cells (PSCs) typically originates from defect centers and strain induced by nonstoichiometric compounds. In this study, we have discovered an excess of PbI2 at the buried interface in inverted wide-band gap PSCs. To address this issue, RbI is introduced to interact with the excessive PbI2, thereby in situ forming a layer of inorganic perovskite RbPbI3. The presence of RbPbI3 as prenucleation centers facilitates intimate contact and enhances crystallinity of the wide-band gap perovskite, thereby alleviating lattice strain and reducing nonradiative recombination centers. Consequently, ion migration is suppressed, and phase segregation at the buried interface is inhibited. After the addition of RbI, the power conversion efficiency (PCE) of the wide-band gap semitransparent device is increased from 17.96 to 19.5%, and the bifacial factor is 83.4%. Furthermore, after continuous illumination at an intensity equivalent to AM 1.5 G for 1000 h, the device based on RbI retains approximately 81.71% of its initial PCE.

Reinforcing Coverage of Self-assembled Monomolecular Layers for Inverted Perovskite Solar Cells with Efficiency of 25.70

Self-assembled monolayers (SAM) as hole transport layers have been widely used in high-efficiency inverted perovskite solar cells (PSCs) exceeded 26 %. However, the poor coverage and non-uniform distribution on the substrate of SAM further restrict the improvement of device performance. Herein, we utilize the mixed SAM strategy via the MeO-2PACz along with perfluorotripropylamine (FC-3283) to improve the SAM coverage, aiming to accelerate the carrier transport, promote the perovskite growth, regulate the surface energy levels and suppress the nonradiative recombination. The champion device with the mixed-SAM achieves an efficiency of 25.70 % (certified efficiency of 25.6 %) with long-term stability (maintained the initial efficiency of 90 % after 1000 h and 180 h under ISOS-L-1 and ISOS-L-2).

Solution-Processed Metal-Oxide Nanoparticles to Prevent The Sputtering Damage in Perovskite/Silicon Tandem Solar Cells

Semitransparent perovskite solar cells (ST-PSCs) for tandem applications typically use a buffer layer deposited via atomic layer deposition (ALD) to protect the cell stack from the damage induced by the sputtering of the transparent electrode. Here, we present a simple yet effective solution-processed buffer layer based on metal-oxide nanoparticles to mitigate sputter-induced damage. We exploit this strategy in a monolithic tandem integrating the optimized ST-PSC on a polished front-side/unpolished rear-side p-type silicon heterojunction (SHJ) solar cell. The intrinsic roughness on the backside significantly boosts the absorption, thus suppressing the need for a dedicated texturization step and leading to a final maximum efficiency of 25.3%. Our findings highlight the potential of solution-processed buffer layers as a practical and scalable solution to mitigate the sputtering damage, as well as the potential of silicon wafers with an unpolished rear surface for enhanced photocurrent.

ALD-Deposited Hydroxyl-Rich NiOx to Enhance SAM Anchoring for Stable and Efficient Perovskite Solar Cells

The interface between nickel oxide (NiOx) and self-assembled monolayers (SAMs) in perovskite solar cells (PSCs) often suffers from limited adsorption strength, poor energy-level alignment, and inadequate defect passivation, which hinder device performance and stability. To address these issues, we introduce a hybrid hole selective layer (HSL) combining atomic layer deposition (ALD)-fabricated NiOx with full-aromatic SAM molecules, creating a highly stable and efficient interface. ALD NiOx, enriched with hydroxyl groups, provides robust adsorption sites for the SAM molecule MeO-PhPACz, ensuring a strong, stable interaction. This hybrid HSL enhances energy-level alignment, hole selectivity, and defect passivation at the NiOx/perovskite interface. Devices utilizing this approach demonstrate significant performance improvements, achieving a power conversion efficiency (PCE) of 21.74%, with reduced voltage losses and minimal hysteresis. Furthermore, operational stability tests reveal enhanced durability under elevated humidity and temperature conditions. These findings highlight the potential of ALD NiOx and SAM hybrid HSL to overcome existing barriers, advancing the commercial viability of PSC technologies.

Micromolecule Postdeposition Process for Highly Efficient Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) have achieved great development, contributed by the advance of self-assembled monolayer (SAM) hole-transporting layers (HTLs) due to their distinctive molecular designability. However, SAM HTLs still present challenges of achieving a compact and ordered surface, resulting in vacancies and defects at the interface as well as adversely affecting the growth of perovskites. In this work, we propose a micromolecule postdeposition process to design the SAM HTL interface and form high-quality perovskites to achieve highly efficient inverted PSCs. We introduce etidronic acid (EA) as a postdeposition micromolecule to fill and reduce vacancies at the SAM interface and to improve growing high-quality perovskites. The postdeposition EA can anchor to the substrate through P-OH anchors, occupying vacancies left by MeO-4PACz, and simultaneously create interaction with perovskites by P═O and C-OH functional groups. The micromolecule postdeposition process effectively fills and reduces vacancies at the SAM interface, passivates defects of perovskites, and facilitates carrier transport. Consequently, a champion PCE of 24.42% is achieved for the target PSCs, which is much higher than the efficiency (20.08%) of the control. This research provides a guided and widely applicable strategy for the development of the SAM interface and further advances the performance of PSCs.

Buried Interface Modulation Using Self-Assembled Monolayer and Ionic Liquid Hybrids for High-Performance Perovskite and Perovskite/CuInGaSe2 Tandem Photovoltaics

Effective modifications for the buried interface between self-assembled monolayers (SAMs) and perovskites are vital for the development of efficient, stable inverted perovskite solar cells (PSCs) and their tandem photovoltaics. Herein, an ionic-liquid-SAM hybrid strategy is developed to synergistically optimize the uniformity of SAMs and the crystallization of perovskites above. Specifically, an ionic liquid of 1-butyl-3-methyl-1H-imidazol-3-iumbis((trifluoromethyl)sulfonyl)amide (BMIMTFSI) is incorporated into the SAM solution, enabling reduced surface roughness, improved wettability, and a more evenly distributed surface potential of the SAM film. Leveraging this optimized substrate, a favorable growth of high-quality perovskite crystals is achieved. Furthermore, the introduced functional ions readily bond with the perovskites, effectively passivating undesirable cation or halide vacancies of the perovskite near the buried interface. Remarkably, high power conversion efficiencies (PCEs) of 25.68% and 22.53% are obtained for normal-bandgap (≈1.55 eV) and wide-bandgap (WBG) (≈1.66 eV) PSCs along with improved operational stability. Additionally, a champion PCE of 19.50% is achieved for semitransparent WBG PSCs, further delivering an impressive PCE of 28.34% for integrated four-terminal tandem photovoltaics when combined with CuInGaSe2 solar cells.

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.

Asymmetric Modification of Carbazole Based Self-Assembled Monolayers by Hybrid Strategy for Inverted Perovskite Solar Cells

Carbazole-based self-assembled molecules (SAMs) are widely applied in inverted perovskite solar cells (iPSCs) due to their unique molecular properties. However, the symmetrical structure of the carbazole-based SAMs makes it difficult to finely regulate their performance, which impedes the further enhancement of the efficiency and stability of iPSCs. This work demonstrates that by constructing an asymmetric carbazole core, 9H-thieno[2',3' : 4,5]thieno[3,2-b]indole) (TTID), the key properties of SAM molecules can be effectively regulated. It has been confirmed that the hybrid thieno[2,3-b]thiophene unit of this asymmetric core governs the energy level, the surface wettability, and the defect passivation capability of the SAMs, while the substituent of core has a greater impact on the molecular dipole and device stability. The synergistic effects from thieno[2,3-b]thiophene and fluorine lead to the KF-derived iPSC demonstrating a certified power conversion efficiency (PCE) of 25.17 % and excellent operational stability. This hybrid design concept offers a promising approach for the further structural modification of SAMs in iPSCs.

Self-Assembled Monolayer-Functionalized NiO Hole Injection layer for Improved Charge Injection in Quantum Dot Light-Emitting Diodes

The development of quantum dot light-emitting diodes (QLEDs) represents a promising advancement in next-generation display technology. However, there are challenges, especially in achieving efficient hole injection, maintaining charge balance, and replacing low-stability organic materials such as PEDOT:PSS. To address these issues, in this study, self-assembled monolayers (SAMs) were employed to modify the surface properties of NiO, a hole injection material, within the structure of ITO/HIL/TFB/QDs/ZnMgO/Al QLEDs. Specifically, using Br-2PACz-based SAMs resulted in surface defect passivation, improved hole injection, reduced exciton quenching, and enhanced electrical characteristics. Notably, QLEDs based on (NiO+Br-2PACz) demonstrated a turn-on voltage of 2.4 V, a maximum external quantum efficiency (EQE) of 8.30%, a maximum luminance of 88,831 cd/m2, and a maximum current efficiency of 32.78 cd/A. Compared to NiO-based QLEDs, these results represent a reduction in turn-on voltage by approximately 1.5 V, a 1.99-fold increase in EQE, and a 3.63-fold increase in luminance, indicating significantly enhanced performance with notable improvements in turn-on voltage, EQE, and luminance. They also showed higher EQE and luminance than PEDOT:PSS-based QLEDs; this could be attributed to the downshifting of energy levels by Br-2PACz, which reduced the hole injection barrier, increased the conductivity, and improved charge balance. In particular, the reduction in exciton quenching and the increase in electrical conductivity contributed significantly to the overall performance enhancement of the (NiO+Br-2PACz)-based QLEDs. This paper proposes a simple method for inorganic hole injection layer functionalize and application.

Bottom Electrode Modification Enables Efficient and Bright Silicon-Based Top-Emission Perovskite Light-Emitting Diodes

The integration of perovskites with mature silicon platform has emerged as a promising approach in the development of efficient on-chip light sources and high-brightness displays. However, the performance of Si-based green perovskite light-emitting diodes (PeLEDs) still falls significantly short compared to their red and near-infrared counterparts. In this study, it is revealed that the high work function Au, widely employed in Si-based top-emission PeLEDs as the reflective bottom electrode, exhibits considerably lower reflectivity in the green spectrum than in the longer wavelengths. Consequently, Ag electrode is introduced to replace Au to enhance the green light reflectivity, and the ultrathin MoO3 and self-assembled monolayers (SAMs) are sequentially deposited for surface modification. These results indicate that the MoO3 layer removes the energy barrier at Ag/polymer hole transport layer interface, enhancing the hole injection efficiency; while the SAMs firmly anchor onto the MoO3 layer, effectively preventing interfacial defect formation. Benefited from this organic/inorganic dual-layer modification strategy, Si-based green PeLEDs with an impressive peak external quantum efficiency of 18.2% and a maximum brightness of 81931 cd m-2 are successfully fabricated, on par with those of the red and near-infrared counterparts. This achievement marks an advancement in developing high-performance Si-based PeLEDs with full-spectrum output.

Engineering of buried interfaces in perovskites: advancing sustainable photovoltaics

Perovskite solar cells (PSCs) have garnered significant attention for their high power conversion efficiency (PCE) and potential for cost-effective, large-scale manufacturing. This comprehensive review focuses on the role of buried interface engineering in enhancing the performance and stability of PSCs with both n-type electron transport layer/perovskite/p-type hole transport layer (n-i-p) and p-type hole transport layer/perovskite/n-type electron transport layer (p-i-n) structures. This study highlights key challenges associated with interface engineering, such as charge extraction, recombination loss, and energy level alignment. Various interface engineering techniques, such as surface passivation, self-assembled monolayers, and additive engineering, are explored in terms of their effectiveness in mitigating recombination loss and improving long-term device stability. This review also provides an in-depth analysis of material selection for the electron and hole transport layers, defect management techniques, and the influence of these on perovskite film quality and device stability. Advanced characterization methods for buried interfaces are discussed, providing insights into the structural, morphological, and electronic properties that govern device performance. Furthermore, we explore emerging approaches that target homogenous cation distribution and phase stability at buried interfaces, both of which are crucial for improving PCEs beyond current benchmarks. By synthesizing the latest research findings and identifying key challenges, this review aims to guide future directions in interface engineering for PSCs and ensure their successful use in next-generation sustainable energy technologies.

Dual Buried Interface Engineering for Improving Air-Processed Inverted FAPbI3 Perovskite Solar Cells

Fabricating perovskite solar cells (PSCs) in an ambient environment provides low-cost preparation routes for solar cells that are suitable for large-scale production. Compared with methylammonium (MA)- based perovskite materials, formamidinium lead iodide (FAPbI3) possesses a more favorable bandgap for light harvesting and better thermostability. However, the phase transition from the α-phase to the δ-phase easily occurs, making it challenging for ambient-air processing. Herein, we develop a buried interface engineering strategy via two molecules including 1,4-bis(diphenylphosphino)butane (DPPB) as well as [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) to optimize air-processed inverted FAPbI3 PSCs. This strategy regulates the crystallization process of the air-fabricated FAPbI3 perovskite film, leading to a purer α-phase with significantly enhanced crystallinity and enlarged grain sizes. Apart from improving the bulk perovskite film, the defects at the NiOx/perovskite interface are passivated, and the energy levels are better matched in the modified device, which facilitates efficient carrier extraction. Resultantly, the target device processed in the open air achieves a dramatically improved power conversion efficiency from 11.37% to 18.45%, in association with an enhanced device stability.

Stereo-Hindrance Induced Conformal Self-Assembled Monolayer for High Efficiency Inverted Perovskite Solar Cells

Self-assembled monolayers (SAMs) are employed as hole-selective contacts in inverted perovskite solar cells (PSCs) and have achieved record power conversion efficiency (PCE) over 26%. However, the tendency of extensively employed SAM [2-(3,6-Dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid to aggregate leads to its uneven coverage to the transparent conducting oxide substrate, which subsequently compromises the photovoltaic performance. Herein, a novel tert-butyl functionalized phosphonic acid carbazole SAM is developed, i.e., (4-(3,6-di-tert-butyl-9H-carbazol-9-yl)butyl)phosphonic acid (tBu-4PACz), and introduced to a mixed SAM system as the hole-extraction layer in inverted PSCs. The stereo-hindrance of the bulky tert-butyl group prevents undesired aggregation and leads to better conformality, which facilitates more efficient hole-extraction and suppresses interfacial recombination losses. The tBu-4PACz SAM-based inverted PSC has achieved record level PCE of 26.25% (26.21%, certificated) with outstanding fill factors over 86%. Moreover, the mixed SAM based inverted PSC devices maintained over 94.7% of their initial efficiency after 500 h continuous maximum power-point tracking under simulation 1-sun irradiation.

Perovskite/Silicon Tandem Solar Cells Above 30% Conversion Efficiency on Submicron-Sized Textured Czochralski-Silicon Bottom Cells with Improved Hole-Transport Layers

In perovskite/silicon tandem solar cells, the utilization of silicon heterojunction (SHJ) solar cells as bottom cells is one of the most promising concepts. Here, we present optimization strategies for the top cell processing and their integration into SHJ bottom cells based on industrial Czochralski (Cz)-Si wafers of 140 μm thickness. We show that combining the self-assembled monolayer [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) with an additional phosphonic acid (PA) with different functional groups, can improve film formation when used as a hole transport layer improving wettability, minimizing shunt fraction and reducing nonradiative losses at the buried interface. Transient surface photovoltage and transient photoluminescence measurements confirm that the combined Me-4PACz/PA layer has similar charge transport properties to Me-4PACz alone. Moreover, this work demonstrates the potential for thin, double-side submicron-sized textured industry-relevant silicon bottom cells yielding a high accumulated short-circuit current density of 40.2 mA/cm2 and reaching a stabilized power conversion efficiency of >30%. This work paves the way toward industry-compatible, highly efficient tandem cells based on a production-compatible SHJ bottom cell.

Inorganic-Derived 0D Perovskite Induced Surface Lattice Arrangement for Efficient and Stable All-Inorganic Perovskite Solar Cells

The inverted inorganic CsPbI3 perovskite solar cells (PSCs) are prospective candidates for next-generation photovoltaics owing to inherent robust thermal/photo-stability and compatibility for tandems. However, the performance and stability of the inverted CsPbI3 PSCs fall behind the n-i-p counterparts due to poor energetic alignment and abundant interfacial defect states. Here, an inorganic 0D Cs4PbBr6 with a good lattice strain arrangement is implemented as the surface anchoring capping layer on CsPbI3. The Cs4PbBr6 perovskite induces enhanced electron-selective junction and thus facilitates efficient charge extraction and effectively inhibits non-radiative recombination. Consequently, the CsPbI3 PSCs with Cs4PbBr6 demonstrate the highest power conversion efficiency (PCE) of CsPbI3-based inverted PSCs, reaching 21.03% PCE from a unit cell and 17.39% PCE from a module with a 64 cm2 aperture area. Furthermore, the resulting devices retain 92.48% after 1000 h under simultaneous 1-sun and damp heat (85 °C / 85% relative humidity) environment.

The Promise and Challenges of Inverted Perovskite Solar Cells

Recently, there has been an extensive focus on inverted perovskite solar cells (PSCs) with a p-i-n architecture due to their attractive advantages, such as exceptional stability, high efficiency, low cost, low-temperature processing, and compatibility with tandem architectures, leading to a surge in their development. Single-junction and perovskite-silicon tandem solar cells (TSCs) with an inverted architecture have achieved certified PCEs of 26.15% and 33.9% respectively, showing great promise for commercial applications. To expedite real-world applications, it is crucial to investigate the key challenges for further performance enhancement. We first introduce representative methods, such as composition engineering, additive engineering, solvent engineering, processing engineering, innovation of charge transporting layers, and interface engineering, for fabricating high-efficiency and stable inverted PSCs. We then delve into the reasons behind the excellent stability of inverted PSCs. Subsequently, we review recent advances in TSCs with inverted PSCs, including perovskite-Si TSCs, all-perovskite TSCs, and perovskite-organic TSCs. To achieve final commercial deployment, we present efforts related to scaling up, harvesting indoor light, economic assessment, and reducing environmental impacts. Lastly, we discuss the potential and challenges of inverted PSCs in the future.

Highly passivated TOPCon bottom cells for perovskite/silicon tandem solar cells

Tunnel oxide passivated contact (TOPCon) silicon solar cells are rising as a competitive photovoltaic technology, seamlessly blending high efficiency with cost-effectiveness and mass production capabilities. However, the numerous defects from the fragile silicon oxide/c-Si interface and the low field-effect passivation due to the inadequate boron in-diffusion in p-type polycrystalline silicon (poly-Si) passivated contact reduce their open-circuit voltages (VOCs), impeding their widespread application in the promising perovskite/silicon tandem solar cells (TSCs) that hold a potential to break 30% module efficiency. To address this, we have developed a highly passivated p-type TOPCon structure by optimizing the oxidation conditions, boron in-diffusion, and aluminium oxide hydrogenation, thus pronouncedly improving the implied VOC (iVOC) of symmetric samples with p-type TOPCon structures on both sides to 715 mV and the VOC of completed double-sided TOPCon bottom cells to 710 mV. Consequently, integrating with perovskite top cells, our proof of concept of 1 cm2 n-i-p perovskite/silicon TSCs exhibit VOCs exceeding 1.9 V and a high efficiency of 28.20% (certified 27.3%), which paves a way for TOPCon cells in the commercialization of future tandems.

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.

Towards the 10-Year Milestone of Monolithic Perovskite/Silicon Tandem Solar Cells

The perovskite/silicon tandem solar cell represents one of the most promising avenues for exceeding the Shockley-Queisser limit for single-junction solar cells at a reasonable cost. Remarkably, its efficiency has rapidly increased from 13.7% in 2015 to 34.6% in 2024. Despite the significant research efforts dedicated to this topic, the "secret" to achieving high-performance perovskite/silicon tandem solar cells seems to be confined to a few research groups. Additionally, the discrepancies in preparation and characterization between single-junction and tandem solar cells continue to impede the transition from efficient single-junction to efficient tandem solar cells. This review first revisits the key milestones in the development of monolithic perovskite/silicon tandem solar cells over the past decade. Then, a comprehensive analysis of the background, advancements, and challenges in perovskite/silicon tandem solar cells is provided, following the sequence of the tandem fabrication process. The progress and limitations of the prevalent stability measurements for tandem devices are also discussed. Finally, a roadmap for designing efficient, scalable, and stable perovskite/silicon tandem solar cells is outlined. This review takes the growth history into consideration while charting the future course of perovskite/silicon tandem research.

A Review: Application of Doped Hydrogenated Nanocrystalline Silicon Oxide in High Efficiency Solar Cell Devices

Due to the unique microstructure of hydrogenated nanocrystalline silicon oxide (nc-SiOx:H), the optoelectronic properties of this material can be tuned over a wide range, which makes it adaptable to different solar cell applications. In this work, the authors review the material properties of nc-SiOx:H and the versatility of its applications in different types of solar cells. The review starts by introducing the growth principle of doped nc-SiOx:H layers, the effect of oxygen content on the material properties, and the relationship between optoelectronic properties and its microstructure. A theoretical analysis of charge carrier transport mechanisms in silicon heterojunction (SHJ) solar cells with wide band gap layers is then presented. Afterwards, the authors focus on the recent developments in the implementation of nc-SiOx:H and hydrogenated amorphous silicon oxide (a-SiOx:H) films for SHJ, passivating contacts, and perovskite/silicon tandem devices.

Improved Hole-Selective Contact Enables Highly Efficient and Stable FAPbBr3 Perovskite Solar Cells and Semitransparent Modules

Self-assembled monolayers (SAMs) as the hole-selective contact have achieved remarkable success in iodine-based perovskite solar cells (PSCs), while their impact on bromine-based PSCs is limited due to the poor perovskite crystallization behavior and mismatched energy level alignment. Here, a highly efficient SAM of (2-(3,6-diiodo-9H-carbazol-9-yl)ethyl)phosphonic acid (I-2PACz) is employed to address these challenges in FAPbBr3-based PSCs. The incorporation of I atoms into I-2PACz not only releases tensile stress within FAPbBr3 perovskite, promoting oriented crystallization and minimizing defects through halogen-halogen bond, but also optimizes the energy levels alignment at hole-selective interface for enhanced hole extraction. Ultimately, a power conversion efficiency (PCE) of 11.14% is achieved, which stands among the highest reported value for FAPbBr3 PSCs. Furthermore, the semitransparent devices/modules exhibit impressive PCEs of 8.19% and 6.23% with average visible transmittance of 41.98% and 38.99%. Remarkably, after operating at maximum power point for 1000 h, the encapsulated device maintains 93% of its initial PCE. These results demonstrate an effective strategy for achieving high-performance bromine-based PSCs toward further applications.

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.

A regulation strategy of self-assembly molecules for achieving efficient inverted perovskite solar cells

Self-assembled monolayers (SAMs) have been successfully employed to enhance the efficiency of inverted perovskite solar cells (PSCs) and perovskite/silicon tandem solar cells due to their facile low-temperature processing and superior device performance. Nevertheless, depositing uniform and dense SAMs with high surface coverage on metal oxide substrates remains a critical challenge. In this work, we propose a holistic strategy to construct composite hole transport layers (HTLs) by co-adsorbing mixed SAMs (MeO-2PACz and 2PACz) onto the surface of the H2O2-modified NiOx layer. The results demonstrate that the conductivity of the NiOx bulk phase is enhanced due to the H2O2 modification, thereby facilitating carrier transport. Furthermore, the hydroxyl-rich NiOx surface promotes uniform and dense adsorption of mixed SAM molecules while enhancing their anchoring stability. In addition, the energy level alignment at the interface is improved due to the utilization of mixed SAMs in an optimized ratio. Furthermore, the perovskite film crystal growth is facilitated by the uniform and dense composite HTLs. As a result, the power conversion efficiency of PSCs based on composite HTLs is boosted from 22.26% to 23.16%, along with enhanced operational stability. This work highlights the importance of designing and constructing NiOx/SAM composite HTLs as an effective strategy for enhancing both the performance and stability of inverted PSCs.

Textured Perovskite/Silicon Tandem Solar Cells Achieving Over 30% Efficiency Promoted by 4-Fluorobenzylamine Hydroiodide

Monolithic textured perovskite/silicon tandem solar cells (TSCs) are expected to achieve maximum light capture at the lowest cost, potentially exhibiting the best power conversion efficiency. However, it is challenging to fabricate high-quality perovskite films and preferred crystal orientation on commercially textured silicon substrates with micrometer-size pyramids. Here, we introduced a bulky organic molecule (4-fluorobenzylamine hydroiodide (F-PMAI)) as a perovskite additive. It is found that F-PMAI can retard the crystallization process of perovskite film through hydrogen bond interaction between F- and FA+ and reduce (111) facet surface energy due to enhanced adsorption energy of F-PMAI on the (111) facet. Besides, the bulky molecular is extruded to the bottom and top of perovskite film after crystal growth, which can passivate interface defects through strong interaction between F-PMA+ and undercoordinated Pb2+/I-. As a result, the additive facilitates the formation of large perovskite grains and (111) preferred orientation with a reduced trap-state density, thereby promoting charge carrier transportation, and enhancing device performance and stability. The perovskite/silicon TSCs achieved a champion efficiency of 30.05% based on a silicon thin film tunneling junction. In addition, the devices exhibit excellent long-term thermal and light stability without encapsulation. This work provides an effective strategy for achieving efficient and stable TSCs.

Efficient and Stable Inverted Perovskite Solar Modules Enabled by Solid-Liquid Two-Step Film Formation

A considerable efficiency gap exists between large-area perovskite solar modules and small-area perovskite solar cells. The control of forming uniform and large-area film and perovskite crystallization is still the main obstacle restricting the efficiency of PSMs. In this work, we adopted a solid-liquid two-step film formation technique, which involved the evaporation of a lead iodide film and blade coating of an organic ammonium halide solution to prepare perovskite films. This method possesses the advantages of integrating vapor deposition and solution methods, which could apply to substrates with different roughness and avoid using toxic solvents to achieve a more uniform, large-area perovskite film. Furthermore, modification of the NiOx/perovskite buried interface and introduction of Urea additives were utilized to reduce interface recombination and regulate perovskite crystallization. As a result, a large-area perovskite film possessing larger grains, fewer pinholes, and reduced defects could be achieved. The inverted PSM with an active area of 61.56 cm2 (10 × 10 cm2 substrate) achieved a champion power conversion efficiency of 20.56% and significantly improved stability. This method suggests an innovative approach to resolving the uniformity issue associated with large-area film fabrication.

Outstanding Fill Factor in Inverted Organic Solar Cells with SnO2 by Atomic Layer Deposition

Transport layers are of outmost importance for thin-film solar cells, determining not only their efficiency but also their stability. To bring one of these thin-film technologies toward mass production, many factors besides efficiency and stability become important, including the ease of deposition in a scalable manner and the cost of the different material's layers. Herein, highly efficient organic solar cells (OSCs), in the inverted structure (n-i-p), are demonstrated by using as electron transport layer (ETL) tin oxide (SnO2) deposited by atomic layer deposition (ALD). ALD is an industrial grade technique which can be applied at the wafer level and also in a roll-to-roll configuration. A champion power conversion efficiency (PCE) of 17.26% and a record fill factor (FF) of 79% are shown by PM6:L8-BO OSCs when using ALD-SnO2 as ETL. These devices outperform solar cells with SnO2 nanoparticles casted from solution (PCE 16.03%, FF 74%) and also those utilizing the more common sol-gel ZnO (PCE 16.84%, FF 77%). The outstanding results are attributed to a reduced charge carrier recombination at the interface between the ALD-SnO2 film and the active layer. Furthermore, a higher stability under illumination is demonstrated for the devices with ALD-SnO2 in comparison with those utilizing ZnO.

Ionic Liquid Modified Polymer Intermediate Layer for Improved Charge Extraction toward Efficient and Stable Perovskite/Silicon Tandem Solar Cells

Monolithic perovskite/silicon tandem solar cells have been attracted much attention in recent years. Despite their high performances, the stability issue of perovskite-based devices is recognized as one of the key challenges to realize industrial application. When comes to the perovskite top subcell, the interface between perovskite and electron transporting layers (usually C60) significantly affects the device efficiency as well as the stability due to their poor adhesion. Here, different from the conventional interfacial passivation using metal fluorides, a hybrid intermediate layer is proposed-PMMA functionalized with ionic liquid (IL)-is introduced at the perovskite/C60 interface. The application of PMMA essentially improves the interfacial stability due to its strong hydrophobicity, while adding IL relieves the charge accumulation between PMMA and the perovskite. Thus, an optimal wide-bandgap perovskite solar cells achieves power conversion efficiency of 20.62%. These cells are further integrated as top subcells with silicon bottom cells in a monolithic tandem structure, presenting an optimized PCE up to 27.51%. More importantly, such monolithic perovskite/silicon cells exhibit superior stability by maintaining 90% of initial efficiency after 1200 h under continuous illumination.

Highly Efficient Monolithic Perovskite/Perovskite/Silicon Triple-Junction Solar Cells

Wide-bandgap metal halide perovskites have demonstrated promise in multijunction photovoltaic (PV) cells. However, photoinduced phase segregation and the resultant low open-circuit voltage (Voc) have greatly limited the PV performance of perovskite-based multijunction devices. Here, a alloying strategy is reported to achieve uniform distribution of triple cations and halides in wide-bandgap perovskites by doping Rb+ and Cl- with small ionic radii, which effectively suppresses halide phase segregation while promoting the homogenization of surface potential. Based on this strategy, a Voc of 1.33 V is obtained from single-junction perovskite solar cells, and a VOC approaching 3.0 V and a power conversion efficiency of 25.0% (obtained from reverse scan direction, certified efficiency: 24.19%) on an 1.04 cm2 photoactive area can be achieved in a perovskite/perovskite/c-Si triple-junction tandem cell, where the certification efficiency is by far the greatest performance of perovskite-based triple-junction tandem solar cells. This work overcomes the performance deadlock of perovskite-based triple-junction tandem cells by setting a materials-by-design paradigm.

Co-Self-Assembled Monolayers Modified NiOx for Stable Inverted Perovskite Solar Cells

[4-(3,6-dimethyl-9H-carbazol-9yl)butyl]phosphonic acid (Me-4PACz) self-assembled molecules (SAM) are an effective method to solve the problem of the buried interface of NiOx in inverted perovskite solar cells (PSCs). However, the Me-4PACz end group (carbazole core) cannot forcefully passivate defects at the bottom of the perovskite film. Here, a Co-SAM strategy is employed to modify the buried interface of PSCs. Me-4PACz is doped with phosphorylcholine chloride (PC) to form a Co-SAM to improve the monolayer coverage and reduce leakage current. The phosphate group and chloride ions (Cl-) in PC can inhibit NiOx surface defects. Meantime, the quaternary ammonium ions and Cl- in PC can fill organic cations and halogen vacancies in the perovskite film to enable defects passivation. Moreover, Co-SAM can promote the growth of perovskite crystals, collaboratively solve the problem of buried defects, suppress nonradiative recombination, accelerate carrier transmission, and relieve the residual stress of the perovskite film. Consequently, the Co-SAM modified devices show power conversion efficiencies as high as 25.09% as well as excellent device stability with 93% initial efficiency after 1000 h of operation under one-sun illumination. This work demonstrates the novel approach for enhancing the performance and stability of PSCs by modifying Co-SAM on NiOx.

Self-Assembled Monolayers for Interfacial Engineering in Solution-Processed Thin-Film Electronic Devices: Design, Fabrication, and Applications

Interfacial engineering has long been a vital means of improving thin-film device performance, especially for organic electronics, perovskites, and hybrid devices. It greatly facilitates the fabrication and performance of solution-processed thin-film devices, including organic field effect transistors (OFETs), organic solar cells (OSCs), perovskite solar cells (PVSCs), and organic light-emitting diodes (OLEDs). However, due to the limitation of traditional interfacial materials, further progress of these thin-film devices is hampered particularly in terms of stability, flexibility, and sensitivity. The deadlock has gradually been broken through the development of self-assembled monolayers (SAMs), which possess distinct benefits in transparency, diversity, stability, sensitivity, selectivity, and surface passivation ability. In this review, we first showed the evolution of SAMs, elucidating their working mechanisms and structure-property relationships by assessing a wide range of SAM materials reported to date. A comprehensive comparison of various SAM growth, fabrication, and characterization methods was presented to help readers interested in applying SAM to their works. Moreover, the recent progress of the SAM design and applications in mainstream thin-film electronic devices, including OFETs, OSCs, PVSCs and OLEDs, was summarized. Finally, an outlook and prospects section summarizes the major challenges for the further development of SAMs used in thin-film devices.

The Development of Carbon/Silicon Heterojunction Solar Cells through Interface Passivation

Passivating contactsin heterojunction (HJ) solar cells have shown great potential in reducing recombination losses, and thereby achieving high power conversion efficiencies in photovoltaic devices. In this direction, carbon nanomaterials have emerged as a promising option for carbon/silicon (C/Si) HJsolar cells due to their tunable band structure, wide spectral absorption, high carrier mobility, and properties such as multiple exciton generation. However, the current limitations in efficiency and active area have hindered the industrialization of these devices. In this review, they examine the progress made in overcoming these constraints and discuss the prospect of achieving high power conversion efficiency (PCE) C/Si HJ devices. A C/Si HJ solar cell is also designed by introducing an innovative interface passivation strategy to further boost the PCE and accelerate the large area preparationof C/Si devices. The physical principle, device design scheme, and performanceoptimization approaches of this passivated C/Si HJ cells are discussed. Additionally, they outline potential future pathways and directions for C/Si HJ devices, including a reduction in their cost to manufacture and their incorporation intotandem solar cells. As such, this review aims to facilitate a deeperunderstanding of C/Si HJ solar cells and provide guidance for their further development.

Impact of the TCO Microstructure on the Electronic Properties of Carbazole-Based Self-Assembled Monolayers

Carbazole-based self-assembled monolayers (PACz-SAMs), anchored via their phosphonic acid group on a transparent conductive oxide (TCO), have demonstrated excellent performance as hole-selective layers in perovskite/silicon tandem solar cells. Yet, whereas different PACz-SAMs have been explored, the role of the TCO, and specifically its microstructure, on the hole transport properties of the TCO/PACz-SAMs stack has been largely overlooked. Here, we demonstrate that the TCO microstructure directly impacts the work function (WF) shift after SAM anchoring and is responsible for WF variations at the micro/nanoscale. Specifically, we studied Sn-doped In2O3 (ITO) substrates with amorphous and polycrystalline (featuring either nanoscale- or microscale-sized grains) microstructures before and after 2PACz-SAMs and NiOx/2PACz-SAMs anchoring. With this, we established a direct correlation between the ITO crystal grain orientation and 2PACz-SAMs local potential distribution, i.e., the WF. Importantly, these variations vanish for amorphous oxides (either in the form of amorphous ITO or when adding an amorphous NiOx buffer layer), where a homogeneous surface potential distribution is found. These findings highlight the importance of TCO microstructure tuning, to enable both high mobility and broadband transparent electrodes while ensuring uniform WF distribution upon application of hole transport SAMs, both critical for enhanced device performance.

Elucidating Charge Carrier Dynamics in Perovskite-Based Tandem Solar Cells

Recently, multijunction tandem solar cells (TSCs) have presented high power conversion efficiency and revealed their immense potential in photovoltaic evolution. It is demonstrated that multiple light absorbers with various bandgap energies overcome the Shockley-Queisser limit of single-junction solar cells by absorbing the wide-range wavelength photons. Here, the main key challenges are reviewed, especially the charge carrier dynamics in perovskite-based 2-terminal (2-T) TSCs in terms of current matching, and how to manage these issues from a vantage point of characterization. To do this, the effect of recombination layers, optical and fabrication hurdles, and the impact of wide bandgap perovskite solar cells are discussed extensively. Afterward, this review focuses on various optoelectronics, spectroscopic, and theoretical (optical simulation) characterizations to figure out those issues, especially current-matching issues faced by the photovoltaic society. This review comprehensively provides deep insights into the relationship between the current-matching problems and the photovoltaic performance of TSCs through a variety of perspectives. Consequently, it is believed that this review is essential to address the main problems of 2-T TSCs, and the suggestions to elucidate the charge carrier dynamics and its characterization may pave the way to overcome such obstacles to further improve the development of 2-T TSCs in relation to the current-matching problems.

Diffusible Capping Layer Enabled Homogeneous Crystallization and Component Distribution of Hybrid Sequential Deposited Perovskite

Nowadays, the development of wide-bandgap perovskite by thermal evaporation and spin-coating hybrid sequential deposition (HSD) method has special meaning on textured perovskite/silicon tandem solar cells. However, the common issues of insufficient reaction caused by blocking of perovskite capping layer are exacerbated in HSD, because evaporated precursors are usually denser with higher crystallinity and the widely used additive-assisted microstructure is also difficult to access. Here, a facile "diffusible perovskite capping layer" (DPCL) strategy to solve this dilemma is presented. With DPCL, crystallization alleviation of perovskite and more diffusion channels of organic salts can be realized simultaneously, contributing to a homogenization process. The resultant perovskite films exhibit complete conversion, uniform crystallization, enhanced quality, and reduced defect, leading to obvious improvements in device efficiency, repeatability, and stability. This work offers a way to promote the development of textured tandems a step further.

Over 19% Efficiency Perovskite Solar Modules by Simultaneously Suppressing Cation Deprotonation and Iodide Oxidation

Perovskite solar cells (PSCs) based on sputtered nickel oxide (NiOx) hole transport layer have emerged as promising configuration due to their good stability, cost-effectiveness, and scalability. However, the adverse chemical redox reaction at the NiOx/perovskite interface remains an ever-present problem that has not yet been well solved. To address this issue before, the problems that cation deprotonation and iodide oxidation that occurred in precursor solution easily result in the interfacial chemical reaction should be prevented. Hence, we report an efficient strategy to simultaneously suppress the interfacial reaction and stabilize the precursor solution by incorporating a reducing and weakly acidic stabilizer, l-ascorbic acid (l-AA). l-AA can reduce I2 generated in the precursor solution and during the interfacial reaction to I-. Furthermore, the protons ionized by adjacent enol hydroxyl groups in l-AA effectively impede the deprotonation of organic cations in the precursor solution as well as at the NiOx/perovskite interface resulting from the chemical reaction. Attributing to the improved crystallization of the perovskite film and the suppression of the interfacial reaction by l-AA, the inverted PSC based on such good light absorber achieves an impressive power conversion efficiency (PCE) of 22.72% along with a high open-circuit voltage of 1.19 V. Notably, further introducing l-AA into the large-area solar modules by the slot-die coating method in air enables a remarkable PCE of 19.17%, which reaches one of the highest PCEs reported for inverted perovskite solar modules (PSMs) (active area >50 cm2) to date. l-AA located at the buried interface also forms a barrier layer that can prevent undesirable chemical reactions at the NiOx/perovskite interface, significantly enhancing the device stability of solar cells and PSMs. These findings in our work provide important guidance for improving the NiOx/perovskite interface and the fabrication of highly efficient, low-cost, and large-area PSMs.

Recent Progress of Wide Bandgap Perovskites towards Two-Terminal Perovskite/Silicon Tandem Solar Cells

Perovskite/silicon tandem solar cells have garnered considerable interest due to their potential to surpass the Shockley-Queisser limit of single-junction Si solar cells. The rapidly advanced efficiencies of perovskite/silicon tandem solar cells benefit from the significant improvements in perovskite technology. Beginning with the evolution of wide bandgap perovskite cells towards two-terminal (2T) perovskite/silicon tandem solar cells, this work concentrates on component engineering, additives, and interface modification of wide bandgap perovskite cells. Furthermore, the advancements in 2T perovskite/silicon tandem solar cells are presented, and the influence of the central interconnect layer and the Si cell on the progression of the tandem solar cells is emphasized. Finally, we discuss the challenges and obstacles associated with 2T perovskite/silicon tandem solar cells, conducting a thorough analysis and providing a prospect for their future.

Pathways toward commercial perovskite/silicon tandem photovoltaics

Perovskite/silicon tandem solar cells offer a promising route to increase the power conversion efficiency of crystalline silicon (c-Si) solar cells beyond the theoretical single-junction limitations at an affordable cost. In the past decade, progress has been made toward the fabrication of highly efficient laboratory-scale tandems through a range of vacuum- and solution-based perovskite processing technologies onto various types of c-Si bottom cells. However, to become a commercial reality, the transition from laboratory to industrial fabrication will require appropriate, scalable input materials and manufacturing processes. In addition, perovskite/silicon tandem research needs to increasingly focus on stability, reliability, throughput of cell production and characterization, cell-to-module integration, and accurate field-performance prediction and evaluation. This Review discusses these aspects in view of contemporary solar cell manufacturing, offers insights into the possible pathways toward commercial perovskite/silicon tandem photovoltaics, and highlights research opportunities to realize this goal.

Homogenized NiOx nanoparticles for improved hole transport in inverted perovskite solar cells

The power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs) is still lagging behind that of conventional PSCs, in part because of inefficient carrier transport and poor morphology of hole transport layers (HTLs). We optimized self-assembly of [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) onto nickel oxide (NiOx) nanoparticles as an HTL through treatment with hydrogen peroxide, which created a more uniform dispersion of nanoparticles with high conductivity attributed to the formation of Ni3+ as well as surface hydroxyl groups for bonding. A 25.2% certified PCE for a mask size of 0.074 square centimeters was obtained. This device maintained 85.4% of the initial PCE after 1000 hours of stabilized power output operation under 1 sun light irradiation at about 50°C and 85.1% of the initial PCE after 500 hours of accelerated aging at 85°C. We obtained a PCE of 21.0% for a minimodule with an aperture area of 14.65 square centimeters.