Advances in Perovskite Solar Cells

Precise Control of Lead Halide and Ammonium Salt Stoichiometric Ratios for Efficient Perovskite Solar Cells

The precise stoichiometric ratio of lead halide and organic ammonium salts is a fundamental yet unresolved scientific challenge in perovskite solar cells (PSCs). Conventional deposition techniques fail to establish a definitive structure-performance relationship due to limitations in quantitative control, leading to inconsistent film quality and ambiguous reaction pathways. In this work, a precise quantitative deposition approach using drop-on-demand inkjet printing to systematically investigate the impact of organic salt deposition surface density on PSC performance is developed. The findings reveal that the deposition amount significantly affects the morphology, composition, and crystallinity of the perovskite films, influencing the overall device performance. Low deposition surface densities below 22 µg cm-2 produce thin perovskite films with incomplete crystallization and small crystals, hindering charge carrier transport and separation. Conversely, a high deposition density (89 µg cm-2) results in over-reaction between the organic salt and PbI2, leading to low-quality perovskite films with pinholes, cracks, and poor interfacial contact. At the optimal deposition density of 39 µg cm-2, it achieves high-quality perovskite films with large grains, reduced defects, and improved energy level alignment, resulting in a champion efficiency of 23.3% and improved environmental stability for the devices.

Revealing the Role of Spacer Length and Methoxy Substitution of Dipodal Indolocarbazole-based SAMs on the Performance of Inverted Perovskite Solar Cells

The application of self-assembled molecules (SAMs) as selective charge transport layers in inverted perovskite solar cells (iPSCs) has attracted significant interest because of their ability to provide high-efficiency and stable devices. In this work, four dipodal SAMs are reported based on π-expanded indolo[2,3-a]carbazole, incorporated as hole-selective contacts in iPSCs. The presence of methoxy substituents and the spacer length in SAMs are modified to assess their influence on the device performance. For that, the ITO/SAM and ITO/SAM/PSCs interfaces are characterized in detail, including theoretical studies and analysis of the complete device performance. These results demonstrate the multifactorial effect that SAMs have on the growth of crystalline perovskite and the charge dynamics in the devices. The resulting iPSCs show power conversion efficiency (PCE) between 19.76% and 22.20% with fill factors exceeding 82% in all cases and good stability under continuous illumination. Notably, SAM combining unsubstituted indolocarbazole and longer pentyl spacer (5CPICZ) shows the highest PCE of 22.20%. In contrast, analogous SAMs with propyl spacers (3CPICZ) achiev a PCE of 22.01%. The experimental results reveal that the improved PCE reached with unsubstituted indolocarbazole SAMs is attributed to reduced charge recombination and longer carrier lifetime owing to effective perovskite surface passivation.

Modulating Activity of Lattice Oxygen of ABO3 Perovskite Oxides in Redox Reactions: A Review

Perovskites, owing to their unique structure, tunable chemical composition, and versatile physicochemical properties, have garnered extensive applications, particularly in redox reactions where the lattice oxygen and/or oxygen vacancies within perovskite are identified as active sites. The modulation of lattice oxygen activity in perovskites is crucial for enhancing the performance of perovskite-type oxides in redox reactions. This review delineates the key factors affecting lattice oxygen activity, including lattice distortions, crystal defects, surface and interface effects, and the migration rate of oxygen ions, and elucidates how these factors synergistically influence the activity of lattice oxygen. A range of strategic approaches, including ionic doping, surface modification, and metal exsolution, are proposed to effectively regulate the behavior and catalytic properties of lattice oxygen. In this investigation, we consolidate a series of analytical and testing methodologies, such as XRD, XPS, ECR, EIS, and TGA, among others, with a focus on lattice oxygen activity, to reveal the fundamental relationship between lattice oxygen activity and the structural and functional attributes of perovskite oxygen carriers. This comprehensive review offers profound insights and guidance for the strategic design and performance optimization of perovskite catalysts or oxygen carriers.

Ti2CTx-MXene as An Efficient Passivation Layer to Regulate the Vertical Growth of Perovskite Layers and Enhance the Performance of Solar Cells

The commercialization of perovskite solar cells (PSCs) is significantly impeded by their limited moisture stability. Integrating an effective passivation layer can serve as a protective barrier, enhancing stability under humid conditions and improving the device's photoelectric performance. In this study, we utilized Ti2CTx-MXene, which was spin-coated onto the perovskite surface, which facilitated controlled vertical crystal growth and simultaneous band gap alignment. Our findings demonstrate that the inclusion of MXene effectively balances charge mobility, resulting in a promising power conversion efficiency (PCE) of 22.22% while maintaining robust stability. This study introduces a top-down approach for controlling perovskite morphology and directional growth, thereby enhancing the photovoltaic performance of the fabricated devices.

Regulation of Interface Schottky Barrier and Photoelectric Properties in Carbon-Based HTL-Free Perovskite Solar Cells

Carbon-based hole transport layer (HTL)-free perovskite solar cells (C-PSCs) receive a lot of attention because of their simplified preparation technology, low price, and good hydrophobicity. However, the Schottky junction formed at the interface between perovskite and carbon poles affects the photogenerated carrier extraction and conversion efficiency. In this paper, 4-trifluoromethyl-2-pyridinecarboxylic acid (TPCA) is used to modify the perovskite films. The introduction of TPCA can reduce the p-type Schottky barrier height (p-SBH) and thin the Schottky barrier width W, which greatly improves the hole transport ability and tunneling probability. Meanwhile, the n-type Schottky barrier height (n-SBH) shows a rising trend, which prevents the reverse electron transport to carbon, suppresses unnecessary carrier complexes, and greatly improves the device's optoelectronic performance. Besides, the pyridine nitrogen and C = O in TPCA interact with Pb2+ to raise the crystal quality of perovskite films while inhibiting nonradiative recombination. The results show that compared with the pristine device's 11.45% photoelectric conversion efficiency （PCE), the TPCA-modified device achieves 13.64% PCE. The device's long-term stability significantly improved post-TPCA modification. After 720 h of storage at room temperature and 40-60% relative humidity in the air, the unencapsulated device retained 77% of its initial efficiency.

The tunable electronic band structure of a AlP3/Cs3Bi2I6Cl3 van der Waals heterostructure induced by an electric field: a first-principles study

Constructing van der Waals heterostructures (vdWHs) has emerged as an attractive strategy to combine and enhance the optoelectronic properties of stacked materials. Herein, by means of first-principles calculations, we investigate the geometric and electronic structures of the AlP3/Cs3Bi2I6Cl3 vdWH as well as its tunable band structure via an external electric field. The AlP3/Cs3Bi2I6Cl3 vdWH is structurally and thermodynamically stable due to the low binding energy and the small energy fluctuation at room temperature. Our band structure calculations demonstrate that the AlP3/Cs3Bi2I6Cl3 vdWH possesses an indirect bandgap and a type-I band alignment with the band edges both dominated by an AlP3 layer. Notably, the band alignment of heterostructures can be flexibly tuned between type-I and type-II by employing an external electric field. Besides, an indirect-to-direct bandgap transition can be observed by increasing the intensity of negative electric field. These results reveal the potential of the AlP3/Cs3Bi2I6Cl3 vdWH as a novel candidate material for the experimental designs of multi-functional devices.

Capillary Force-Assisted CsPbBr3-xIx (x = 0, 1) Columnar Crystal Film for X-ray Detectors with Ultrahigh Electric Field and Sensitivity

Inorganic halide perovskite thin-film X-ray detectors have attracted great research interest in recent years due to their high sensitivity, low detection limit, and facile fabrication process. The poor crystal quality of the thin film with uncontrollable thickness and low background voltage during detection limits its practical application. Here, a high-quality CsPbBr3-xIx (x = 0, 1) columnar crystal film is prepared by an improved melt-confined method with a porous anodic aluminum oxide (AAO) template, which stabilizes the disorder perovskite systems of CsPbBr2I by stress. The AAO-CsPbBr3-xIx (x = 0) detectors exhibit high detection accuracy and photoelectric conversion capability with an ultrahigh sensitivity of 32,399.5 μC·Gyair-1·cm-2 at 2142.9 V mm-1 under 20 kVp X-rays and 19,217.4 μC·Gyair-1·cm-2 with a higher background electric field of 6666.7 V mm-1 for AAO-CsPbBr3-xIx (x = 1). Moreover, the AAO-CsPbBr3-xIx (x = 1) film detector acquires a lower detection limit of 7.65 nGy·s-1 and a higher X-ray imaging spatial resolution of 1.6 LP/mm and 8.6 nGy·s-1 and 1.4 LP/mm for AAO-CsPbBr3-xIx (x = 0). The facile, high-quality columnar crystal film devices display great potential for low-energy and low-dose X-ray imaging in flat panel detection applications.

Light Absorption-Enhanced Ultra-Thin Perovskite Solar Cell Based on Cylindrical MAPbI3 Microstructure

In order to promote power conversion efficiency and reduce energy loss, we propose a perovskite solar cell based on cylindrical MAPbI3 microstructure composed of a MAPbI3 perovskite layer and a hole transport layer (HTL) composed of PEDOT:PSS. According to the charge transport theory, which effectually increases the contact area of the HTL, promoting the electronic transmission capability, the local field enhancement and scattering effects of the surface plasmon polaritons help to couple the incident light to the solar cell, which can increase the absorption of light in the active layer of the solar cell and improve its light absorption efficiency (LAE). based on simulation results, a cylindrical microstructure of the perovskite layer increases the contact area of the hole transport layer, which could improve light absorption, quantum efficiency (QE), short-circuit current density (JSC), and electric power compared with the perovskite layer of other structures. In the AM 1.5 solar spectrum, the average light absorption efficiency is 93.86%, the QE is 80.7%, the JSC is 24.50 mA/cm2, and the power conversion efficiency (PCE) is 20.19%. By enhancing the efficiency and reducing material usage, this innovative design approach for perovskite solar cells is expected to play a significant role in advancing solar technology and positively impacting the development of renewable energy solutions.

High-Temperature Driven Recrystallization for Stable Dopant-Free α-FAPbI3 Perovskite Solar Cells

High temperatures facilitate the formation of stable, high-crystallinity α-FAPbI3 films but can lead to the volatilization of organic components in perovskites. Here, a 300 °C hot-press-assisted recrystallization strategy is reported to grow stable phase-pure α-FAPbI3 film without any dopants. High temperature can promote the transformation of δ-FAPbI3 to α-FAPbI3, and induces recrystallization to relieve strain. The applied pressure creates a confined space that effectively prevents the volatilization of organic components in perovskite. The α-FAPbI3 film prepared by hot-press at 300 °C achieves an average grain size of ≈3 µm (with grains up to 10 µm) and demonstrates excellent damp-heat stability, showing no significant change after 20 s in deionized water. The result solar cell delivers a power conversion efficiency as high as 24.06% and retains >70% of their initial efficiency value after 1000 h at 85 °C and 85% relative humidity.

Influence of F-Containing Materials on Perovskite Solar Cells

Perovskite solar cells (PSCs) are usually modified and passivated to improve their performance and stability. The interface modification and bulk doping are the two basic strategies. Fluorine (F)-containing materials are highly favored because of their unique hydrophobicity and coordination ability. This review discusses the basic characteristics of F, and the basic principles of improving the photovoltaic performance and stability of PSC devices using F-containing materials. We systematically summarized the latest progress in the application of F-containing materials to achieve efficient and stable PSCs on several key interface layers. It is believed that this work will afford significant understanding and inspirations toward the future application directions of F-containing materials in PSCs, and provide profound insights for the development of efficient and stable PSCs.

Machine learning-enhanced band gaps prediction for low-symmetry double and layered perovskites

Density functional theory (DFT) calculations are widely used for material property prediction, but their computational cost can hinder the discovery of novel perovskites. This work explores machine learning (ML) as a faster alternative for predicting band gaps in complex perovskites, focusing on low-symmetry double and layered structures. We employ Support Vector Regression (SVR), Random Forest Regression (RFR), Gradient Boosting Regression (GBR), and Extreme Gradient Boosting (XGBoost) to predict both direct and indirect band gaps. Model performance is evaluated using Mean Absolute Error (MAE), Mean Squared Error (MSE), and R-squared (R²) metrics. Our results reveal SVR as the most effective general model for predicting band gaps in both double and layered perovskites. Interestingly, for double perovskites specifically, XGBoost achieves even higher accuracy when incorporating derivative discontinuity as a feature. Feature importance analysis identifies the standard deviation of valence charges ("Valence (std)") as the most critical factor for band gap prediction across all studied perovskites. This research demonstrates the potential of ML for efficient and accurate band gap prediction in complex perovskites, accelerating material discovery efforts.

Innovative Approaches to Large-Area Perovskite Solar Cell Fabrication Using Slit Coating

Perovskite solar cells (PSCs) are gaining prominence in the photovoltaic industry due to their exceptional photoelectric performance and low manufacturing costs, achieving a significant power conversion efficiency of 26.4%, which closely rivals that of silicon solar cells. Despite substantial advancements, the effective area of high-efficiency PSCs is typically limited to about 0.1 cm2 in laboratory settings, with efficiency decreasing as the area increases. The limitation poses a major obstacle to commercialization, as large-area, high-quality perovskite films are crucial for commercial applications. This paper reviews current techniques for producing large-area perovskites, focusing on slot-die coating, a method that has attracted attention for its revolutionary potential in PSC manufacturing. Slot-die coating allows for precise control over film thickness and is compatible with roll-to-roll systems, making it suitable for large-scale applications. The paper systematically outlines the characteristics of slot-die coating, along with its advantages and disadvantages in commercial applications, suggests corresponding optimization strategies, and discusses future development directions to enhance the scalability and efficiency of PSCs, paving the way for broader commercial deployment.

Photothermal Conversion Porous Organic Polymers: Design, Synthesis, and Applications

Solar energy is a primary form of renewable energy, and photothermal conversion is a direct conversion process with tunable conversion efficiency. Among various kinds of photothermal conversion materials, porous organic polymers (POP) are widely investigated owing to their controllable molecular design, tailored porous structures, good absorption of solar light, and low thermal conductivity. A variety of POP, such as conjugated microporous polymers (CMP), covalent organic frameworks (COF), hyper-crosslinked porous polymers (HCP), polymers of intrinsic microporosity (PIM), porous ionic polymers (PIP), are developed and applied in photothermal conversion applications of seawater desalination, latent energy storage, and biomedical fields. In this review, a comprehensive overview of the recent advances in POP for photothermal conversion is provided. The micro molecular structure characteristics and macro morphology of POP are designed for applications such as seawater desalination, latent heat energy storage, phototherapy and photodynamic therapy, and drug delivery. Besides, a probe into the underlying mechanism of structural design for constructing POP with excellent photothermal conversion performance is methodicalized. Finally, the remaining challenges and prospective opportunities for the future development of POP for solar energy-driven photothermal conversion applications are elucidated.

Interface Defects Dependent on Perovskite Annealing Temperature for NiOX-Based Inverted CsPbI2Br Perovskite Solar Cells

Nickel oxide (NiOX) is an ideal inorganic hole transport material for the fabrication of inverted perovskite solar cells owing to its excellent optical and semiconductor properties. Currently, the main research on developing the performance of NiOX-based perovskite solar cells focuses on improving the conductivity of NiOX thin films and preventing the redox reactions between metal cations (Ni3+ on the surface of NiOX) and organic cations (FA+ or MA+ in the perovskite precursors) at the NiOX/perovskite interface. In this study, a new type of interface defects in NiOX-based CsPbI2Br solar cells is reported. That is the Pb2+ from CsPbI2Br perovskites can diffuse into the lattice of NiOX surface as the annealing temperature of perovskites changes. The diffusion of Pb2+ increases the ratio of Ni3+/Ni2+ on the surface of NiOX, leading to an increase in the density of trap state at the interface between NiOX and perovskites, which eventually results in a serious decline in the photovoltaic performance of solar cells.

Dense Perovskite Thick Film Enabled by Saturated Solution Filling for Sensitive X-ray Detection and Imaging

Thick polycrystalline perovskite films synthesized by using solution processes show great potential in X-ray detection applications. However, due to the evaporation of the solvent, many pinholes and defects appear in the thick films, which deteriorate their optoelectronic properties and diminish their X-ray detection performance. Therefore, the preparation of large area and dense perovskite thick films is desired. Herein, we propose an effective strategy of filling the pores with a saturated precursor solution. By adding the saturated perovskite solution to the polycrystalline perovskite thick film, the original perovskite film will not be destroyed because of the solution-solute equilibrium relationship. Instead, it promotes in situ crystal growth within the thick film during the annealing process. The loosely packed grains in the original thick perovskite film are connected, and the pores and defects are partially filled and fixed. Finally, a much denser perovskite thick film with improved optoelectronic properties has been obtained. The optimized thick film exhibits an X-ray sensitivity of 1616.01 μC Gyair-1 cm-2 under an electric field of 44.44 V mm-1 and a low detection limit of 28.64 nGyair s-1 under an electric field of 22.22 V mm-1. These values exceed the 323.86 μC Gyair-1 cm-2 and 40.52 nGyair s-1 of the pristine perovskite thick film measured under the same conditions. The optimized thick film also shows promising working stability and X-ray imaging capability.

Accelerated Design for Perovskite-Oxide-Based Photocatalysts Using Machine Learning Techniques

The rapid discovery of photocatalysts with desired performance among tens of thousands of potential perovskites represents a significant advancement. To expedite the design of perovskite-oxide-based photocatalysts, we developed a model of ABO3-type perovskites using machine learning methods based on atomic and experimental parameters. This model can be used to predict specific surface area (SSA), a key parameter closely associated with photocatalytic activity. The model construction involved several steps, including data collection, feature selection, model construction, web-service development, virtual screening and mechanism elucidation. Statistical analysis revealed that the support vector regression model achieved a correlation coefficient of 0.9462 for the training set and 0.8786 for the leave-one-out cross-validation. The potential perovskites with higher SSA than the highest SSA observed in the existing dataset were identified using the model and our computation platform. We also developed a webserver of the model, freely accessible to users. The methodologies outlined in this study not only facilitate the discovery of new perovskites but also enable exploration of the correlations between the perovskite properties and the physicochemical features. These findings provide valuable insights for further research and applications of perovskites using machine learning techniques.

Polaronic Mass Enhancement and Polaronic Excitons in Metal Halide Perovskites

In metal halide perovskites, the complex dielectric screening together with low energy of phonon modes leads to non-negligible Fröhlich coupling. While this feature of perovskites has already been used to explain some of the puzzling aspects of carrier transport in these materials, the possible impact of polaronic effects on the optical response, especially excitonic properties, is much less explored. Here, with the use of magneto-optical spectroscopy, we revealed the non-hydrogenic character of the excitons in metal halide perovskites, resulting from the pronounced Fröhlich coupling. Our results can be well described by the polaronic-exciton picture where electron and hole interactions are no longer described by a Coulomb potential. Furthermore, we show experimental evidence that the carrier-phonon interaction leads to the enhancement of the carrier's effective mass. Notably, our measurements reveal a pronounced temperature dependence of the carrier's effective mass, which we attribute to a band structure renormalization induced by the population of low-energy phonon modes. This interpretation finds support in our first-principles calculations.

Fabrication of Erbium-Doped Upconversion Nanoparticles and Carbon Quantum Dots for Efficient Perovskite Solar Cells

Upconversion nanoparticles (UCNPs) and carbon quantum dots (CQDs) have emerged as promising candidates for enhancing both the stability and efficiency of perovskite solar cells (PSCs). Their rising prominence is attributed to their dual capabilities: they effectively passivate the surfaces of perovskite-sensitive materials while simultaneously serving as efficient spectrum converters for sunlight. In this work, we synthesized UCNPs doped with erbium ions as down/upconverting ions for ultraviolet (UV) and near-infrared (NIR) light harvesting. Various percentages of the synthesized UCNPs were integrated into the mesoporous layers of PSCs. The best photovoltaic performance was achieved by a PSC device with 30% UCNPs doped in the mesoporous layer, with PCE = 16.22% and a fill factor (FF) of 74%. In addition, the champion PSCs doped with 30% UCNPs were then passivated with carbon quantum dots at different spin coating speeds to improve their photovoltaic performance. When compared to the pristine PSCs, a fabricated PSC device with 30% UCNPs passivated with CQDs at a spin coating speed of 3000 rpm showed improved power conversion efficiency (PCE), from 16.65% to 18.15%; a higher photocurrent, from 20.44 mA/cm2 to 22.25 mA/cm2; and a superior fill factor (FF) of 76%. Furthermore, the PSCs integrated with UCNPs and CQDs showed better stability than the pristine devices. These findings clear the way for the development of effective PSCs for use in renewable energy applications.

Investigation of Perovskite Solar Cells Using Guanidinium Doped MAPbI3 Active Layer

In this work, guanidinium (GA+) was doped into methylammonium lead triiodide (MAPbI3) perovskite film to fabricate perovskite solar cells (PSCs). To determine the optimal formulation of the resulting guanidinium-doped MAPbI3 ((GA)x(MA)1-xPbI3) for the perovskite active layer in PSCs, the perovskite films with various GA+ doping concentrations, annealing temperatures, and thicknesses were systematically modulated and studied. The experimental results demonstrated a 400-nm-thick (GA)x(MA)1-xPbI3 film, with 5% GA+ doping and annealed at 90 °C for 20 min, provided optimal surface morphology and crystallinity. The PSCs configured with the optimal (GA)x(MA)1-xPbI3 perovskite active layer exhibited an open-circuit voltage of 0.891 V, a short-circuit current density of 24.21 mA/cm2, a fill factor of 73.1%, and a power conversion efficiency of 15.78%, respectively. Furthermore, the stability of PSCs featuring this optimized (GA)x(MA)1-xPbI3 perovskite active layer was significantly enhanced.

A bromide substituted 2D additive for stable and efficient perovskite photovoltaics

In this article, a bromide substituted 2D layered perovskite having a repeated vertical orientation and coexisting with the bulk of a 3D perovskite is reported for the first time. This novel structure is obtained through controlled compositional engineering of the perovskite precursor solution. The photovoltaic performance of this novel 2D/3D perovskite was higher than that of 3D MAPbI3 and a maximum photoconversion efficiency (PCE) of 17.4% was achieved. The devices fabricated using this perovskite heterostructure were stable and retained their initial PCE up to 20 days when kept open in a laboratory environment with 40% relative humidity.

Sulfonate-Containing Polyelectrolytes for Perovskite Modification: Chemical Configuration, Property, and Performance

Three sulfonate-containing polyelectrolytes are elaborately designed and used to passivate perovskite film with the anti-solvent method. Under the influence of the secondary monomer, three copolymers present various chemical configurations and deliver different modification effects. Fluorene-thiophene copolymer STF has linear and highly-conjugated chain. STF-perovskite film presents large crystal grains. Fluorene-carbazole copolymer SCF has flexible chain and easily enters into grain boundary areas. SCF-perovskite film is homogenous and continuous. Fluorene-fluorene copolymer SPF agglomerates on the surface and is not applicable to the anti-solvent method. The full investigation demonstrates that STF and SCF not only conduct surface defect passivation, but also improve the film quality by being involved in the perovskite's crystallization process. Compared with the control device, the devices with STF and SCF deliver high efficiency and excellent stability. The unencapsulated devices with STF and SCT maintain ≈80% of the initial power conversion efficiency (PCE) after 40 days of storage under 30-40% relative humidity. SCF performs better and the device maintains 60% of the initial PCE after 20 days of storage under 60-80% relative humidity.

Designing of fluorine-substituted benzodithiophene-based small molecules with efficient photovoltaic parameters

In this study, four hole-transporting materials (JY-M1, JY-M2, JY-M3, and JY-M4) are designed by modifying benzothiadiazole-based core with diphenylamine-based carbazole via acceptors through thiophene linkers. The designed molecules exhibited deeper HOMO energy with smaller energy gaps than the reference JY molecule which enhance their hole mobility. The absorption spectra of the JY-M1, JY-M2, JY-M3, and JY-M4 molecules are located at 380 nm to 407 nm in the gaseous phase and 397 nm to 433 nm in the solvent phase, which is red-shifted and higher than the reference molecule, demonstrating that designed molecules possess improved light absorption properties and enhanced effective hole transfer. The dipole moments of the designed molecules (14.74 D to 26.12 D) indicate a greater ability for charge separation, solubility and will be beneficial to produce multilayer films. Moreover, the results of hole reorganization energy (0.38198 eV to 0.45304 eV) and charge transfer integral (0.14315 eV to 0.14665 eV) of designing molecules show improved hole mobility and lower recombination losses compared to the JY molecule. Overall, we suggested that the structural modifications in the designed molecules contributed to their enhanced efficiency in converting light energy into electrical energy and have the potential for utilization in solar devices, paving the way for future advancements in the field of photovoltaics.

Design of optimized photonic-structure and analysis of adding a SiO2 layer on the parallel CH3NH3PbI3/CH3NH3SnI3 perovskite solar cells

So far, remarkable achievements have been obtained by optimizing the device architecture and modeling of solar cells is a precious and very effective way to comprehend a better description of the physical mechanisms in solar cells. As a result, this study has inspected two-dimensional simulation of perovskite solar cells (PSCs) to achieve a precise model. The solution which has been employed is based on the finite element method (FEM). First, the periodically light trapping (LT) structure has been replaced with a planar structure. Due to that, the power conversion efficiency (PCE) of PSC was obtained at 14.85%. Then, the effect of adding an SiO2 layer to the LT structure as an anti-reflector layer was investigated. Moreover, increasing the PCE of these types of solar cells, a new structure including a layer of CH3NH3SnI3 as an absorber layer was added to the structure of PSCs in this study, which resulted in 25.63 mA/cm2 short circuit current (Jsc), 0.96 V open circuit voltage (Voc), and 20.48% PCE.

Mono- and Co-Doped Mn-Doped CsPbCl3 Perovskites with Enhanced Doping Efficiency and Photoluminescent Performance

To investigate the effect of Mn and other metal dopants on the photoelectronic performance of CsPbCl3 perovskites, we conducted a series of theoretical analyses. Our findings showed that after Mn mono-doping, the CsPbCl3 lattice contracted and the bonding strength increased, resulting in a more compact structure of the metal octahedral cage. The relaxation of the metal octahedral cage, along with the Jahn-Teller effect, results in a decrease in lattice strain between the octahedra and a reduction in the energy of the entire lattice due to the deformation of the metal octahedron. These three factors work together to reduce intrinsic defects and enhance the stability and electronic properties of CsPbCl3 perovskites. The solubility of the Mn dopant is significantly increased when co-doped with Ni, Fe, and Co dopants, as it compensates for the lattice strain induced by Mn. Doping CsPbCl3 perovskites reduces the band gap due to the decreased contributions of 3d orbitals from the dopants. Our analyses have revealed that strengthening the CsPbCl3 lattice and reducing intrinsic defects can result in improved stability and PL properties. Moreover, increasing Mn solubility and decreasing the bandgap can enhance the PLQY of orange luminescence in CsPbCl3 perovskites. These findings offer valuable insights for the development of effective strategies to enhance the photoelectronic properties of these materials.

Modulating Crystallization and Defect Passivation by Butyrolactone Molecule for Perovskite Solar Cells

The attainment of a well-crystallized photo-absorbing layer with minimal defects is crucial for achieving high photovoltaic performance in polycrystalline solar cells. However, in the case of perovskite solar cells (PSCs), precise control over crystallization and elemental distribution through solution processing remains a challenge. In this study, we propose the use of a multifunctional molecule, α-amino-γ-butyrolactone (ABL), as a modulator to simultaneously enhance crystallization and passivate defects, thereby improving film quality and deactivating nonradiative recombination centers in the perovskite absorber. The Lewis base groups present in ABL facilitate nucleation, leading to enhanced crystallinity, while also retarding crystallization. Additionally, ABL effectively passivates Pb²⁺ dangling bonds, which are major deep-level defects in perovskite films. This passivation process reduces recombination losses, promotes carrier transfer and extraction, and further improves efficiency. Consequently, the PSCs incorporating the ABL additive exhibit an increase in conversion efficiency from 18.30% to 20.36%, along with improved long-term environmental stability. We believe that this research will contribute to the design of additive molecular structures and the engineering of components in perovskite precursor colloids.

A2Bn-1PbnI3n+1 (A = BA, PEA; B = MA; n = 1, 2): Engineering Quantum-Well Crystals for High Mass Density and Fast Scintillators

Quantum-well (QW) hybrid organic-inorganic perovskite (HOIP) crystals, e.g., A₂PbX₄ (A = BA, PEA; X = Br, I), demonstrated significant potentials as scintillating materials for wide energy radiation detection compared to their individual three-dimensional (3D) counterparts, e.g., BPbX₃ (B = MA). Inserting 3D into QW structures resulted in new structures, namely A₂BPb₂X₇ perovskite crystals, and they may have promising optical and scintillation properties toward higher mass density and fast timing scintillators. In this article, we investigate the crystal structure as well as optical and scintillation properties of iodide-based QW HOIP crystals, A₂PbI₄ and A₂MAPb₂I₇. A₂PbI₄ crystals exhibit green and red emission with the fastest PL decay time <1 ns, while A₂MAPb₂I₇ crystals exhibit a high mass density of >3.0 g/cm³ and tunable smaller bandgaps <2.1 eV resulting from quantum and dielectric confinement. We observe that A₂PbI₄ and PEA₂MAPb₂I₇ show emission under X- and γ-ray excitations. We further observe that some QW HOIP iodide scintillators exhibit shorter radiation absorption lengths (∼3 cm at 511 keV) and faster scintillation decay time components (∼0.5 ns) compared to those of QW HOIP bromide scintillators. Finally, we investigate the light yields of iodide-based QW HOIP crystals at 10 K (∼10 photons/keV), while at room temperature they still show pulse height spectra with light yields between 1 and 2 photons/keV, which is still >5 times lower than those for bromides. The lower light yields can be the drawbacks of iodide-based QW HOIP scintillators, but the promising high mass density and decay time results of our study can provide the right pathway for further improvements toward fast-timing applications.

A study on theoretical models for investigating time-resolved photoluminescence in halide perovskites

Time-resolved photoluminescence (TRPL) is an effective experimental technique to study charge carrier dynamic processes in halide perovskites on different time scales. In the past decade, several models have been proposed and employed to study the TRPL curves in halide perovskites, but there is still a lack of systematic summarization and comparative discussion. Here, we reviewed the widely employed exponential models to fit the TRPL curves, and focused on the physical meaning of the extracted carrier lifetimes, as well as the existing debates on the definition of the average lifetime. Emphasis was placed on the importance of the diffusion process in the carrier dynamics, especially for the halide perovskite thin films having transport layers. The solving of the diffusion equation, using both analytical and numerical methods, was then introduced to fit the TRPL curves. Furthermore, the newly proposed global fit and direct measurement of radiative decay rates were discussed.

Functional Fiber Materials to Smart Fiber Devices

The development of fiber materials has accompanied the evolution of human civilization for centuries. Recent advances in materials science and chemistry offered fibers new applications with various functions, including energy harvesting, energy storing, displaying, health monitoring and treating, and computing. The unique one-dimensional shape of fiber devices endows them advantages to work as human-interfaced electronics due to the small size, lightweight, flexibility, and feasibility for integration into large-scale textile systems. In this review, we first present a discussion of the basics of fiber materials and the design principles of fiber devices, followed by a comprehensive analysis on recently developed fiber devices. Finally, we provide the current challenges facing this field and give an outlook on future research directions. With novel fiber devices and new applications continuing to be discovered after two decades of research, we envision that new fiber devices could have an important impact on our life in the near future.

Interface Engineering at Sc2C MXene and Germanium Iodine Perovskite Interface: First-Principles Insights

In recent years, Ge-based halide perovskite has gained increasing attention due to its potential in the development of lead-free perovskite solar cells. Here, through first-principles calculations, we explored the possibilities to enhance the optoelectronic properties of Ge-based perovskites via interfacial engineering between germanium iodine perovskite and 2D scandium-carbide MXene with various termination groups including F, O, and OH. We first evaluated the relative stability of the material interfaces and found that MAI-terminated interfaces are energetically more favorable than the GeI₂-terminated interfaces. The MAI/F interface exhibits a type-II band alignment that can promote the photogenerated electron-hole separation. Moreover, the work function of the heterostructures can be tuned from 2.60 to 4.45 eV via using various termination groups. Additionally, 2D Sc₂C MXene can also significantly enhance the light absorption. These results indicate that the 2D MXene serves as one promising candidate for optimizing the properties of perovskite solar cells via interface engineering.

Recent advances in developing high-performance organic hole transporting materials for inverted perovskite solar cells

Inverted perovskite solar cells (PVSCs) have recently made exciting progress, showing high power conversion efficiencies (PCEs) of 25% in single-junction devices and 30.5% in silicon/perovskite tandem devices. The hole transporting material (HTM) in an inverted PVSC plays an important role in determining the device performance, since it not only extracts/transports holes but also affects the growth and crystallization of perovskite film. Currently, polymer and self-assembled monolayer (SAM) have been considered as two types of most promising HTM candidates for inverted PVSCs owing to their high PCEs, high stability and adaptability to large area devices. In this review, recent encouraging progress of high-performance polymer and SAM-based HTMs is systematically reviewed and summarized, including molecular design strategies and the correlation between molecular structure and device performance. We hope this review can inspire further innovative development of HTMs for wide applications in highly efficient and stable inverted PVSCs and the tandem devices.

Organic Hole-Transport Layers for Efficient, Stable, and Scalable Inverted Perovskite Solar Cells

Hole-transporting layers (HTLs) are an essential component in inverted, p-i-n perovskite solar cells (PSCs) where they play a decisive role in extraction and transport of holes, surface passivation, perovskite crystallization, device stability, and cost. Currently, the exploration of efficient, stable, highly transparent and low-cost HTLs is of vital importance for propelling p-i-n PSCs toward commercialization. Compared to their inorganic counterparts, organic HTLs offer multiple advantages such as a tunable bandgap and energy level, easy synthesis and purification, solution processability, and overall low cost. Here, recent progress of organic HTLs, including conductive polymers, small molecules, and self-assembled monolayers, as utilized in inverted PSCs is systematically reviewed and summarized. Their molecular structure, hole-transport properties, energy levels, and relevant device properties and resulting performances are presented and analyzed. A summary of design principles and a future outlook toward highly efficient organic HTLs in inverted PSCs is proposed. This review aims to inspire further innovative development of novel organic HTLs for more efficient, stable, and scalable inverted PSCs.

How to (Not) Make a Perovskite Solar Panel: A Step-by-Step Process

To date, scientific research on perovskite solar cells (PSCs) and modules (PSMs) has been carried out for more than 10 years. What is still missing in the market potential of this technology is a complete description of the materials needed to connect and fabricate PSMs in order to build a perovskite solar panel. Starting from the state-of-the-art perovskite solar modules, the material and design optimization using different substrates and architecture types, and ending in the lamination of the panel, this work focusses on the study of the feasibility of the fabrication of a perovskite solar panel. A complete description of all steps required will be provided in detail.

Defect Passivation via Isoxazole Doping in Perovskite Solar Cells

To improve perovskite solar cell (PSC) performance, which is deeply related to perovskite layer quality, researchers have explored numerous strategies. Additive doping into perovskite precursors has been widely used to improve the PSC performance. In this study, we used isoxazole-a Lewis-base small molecule-as an additive for the CH3NH3PbI3 (MAPbI3) precursor and explored how isoxazole effectively passivates defects in the perovskite structure. We found that isoxazole interacted with undercoordinated Pb2+ ions from an X-ray photoelectron spectroscopy survey and verified that isoxazole doping improved the device performance. When the optimized concentration of isoxazole was doped in the MAPbI3 precursor, the power conversion efficiency increased from 15.6 to 17.5%, with an improved fill factor and short-circuit current density. In addition, an isoxazole-doped device sustained 94% of its initial performance after 8 days under ambient air conditions (10 ± 5 RH %, 25 °C), whereas a device without isoxazole doping only maintained 64% of its initial performance.

Defect Passivation by a Multifunctional Phosphate Additive toward Improvements of Efficiency and Stability of Perovskite Solar Cells

The quality of perovskite films plays a crucial role in the performance of the corresponding devices. However, the commonly employed perovskite polycrystalline films often contain a high density of defects created during film production and cell operation, including unsaturated coordinated Pb²⁺ and Pb⁰, which can act as nonradiative recombination centers, thus reducing open-circuit voltage. Effectively eliminating both kinds of defects is an important subject of research to improve the power conversion efficiency (PCE). Here, we employ hydrogen octylphosphonate potassium (KHOP) as a multifunctional additive to passivate defects. The molecule is introduced into perovskite precursor solution to regulate the perovskite film growth process by coordinating with Pb, which can not only passivate the Pb²⁺ defect but also effectively inhibit the production of Pb⁰; at the same time, the presence of K⁺ reduces device hysteresis by inhibiting I^- migration and finally realizes double passivation of Pb²⁺ and I^--based defects. Moreover, the moderate hydrophobic alkyl chain in the molecule improves the moisture stability. Ultimately, the optimal efficiency can reach 22.21%.

Hydrogenated Cs2AgBiBr6 for significantly improved efficiency of lead-free inorganic double perovskite solar cell

Development of lead-free inorganic perovskite material, such as Cs₂AgBiBr₆, is of great importance to solve the toxicity and stability issues of traditional lead halide perovskite solar cells. However, due to a wide bandgap of Cs₂AgBiBr₆ film, its light absorption ability is largely limited and the photoelectronic conversion efficiency is normally lower than 4.23%. In this text, by using a hydrogenation method, the bandgap of Cs₂AgBiBr₆ films could be tunable from 2.18 eV to 1.64 eV. At the same time, the highest photoelectric conversion efficiency of hydrogenated Cs₂AgBiBr₆ perovskite solar cell has been improved up to 6.37% with good environmental stability. Further investigations confirmed that the interstitial doping of atomic hydrogen in Cs₂AgBiBr₆ lattice could not only adjust its valence and conduction band energy levels, but also optimize the carrier mobility and carrier lifetime. All these works provide an insightful strategy to fabricate high performance lead-free inorganic perovskite solar cells.

Though inorganic perovskites are an attractive, non-toxic and stable alternative to organic-inorganic halide perovskite solar cells, realizing efficient devices remains a challenge. Here, the authors report hydrogenated lead-free inorganic perovskite solar cells with enhanced power conversion efficiency.

Efficient and Stable Perovskite Solar Cells Based on Inorganic Hole Transport Materials

Although power conversion efficiencies of organic-inorganic lead halide perovskite solar cells (PSCs) are approaching those of single-crystal silicon solar cells, the working device stability due to internal and external factors, such as light, temperature, and moisture, is still a key issue to address. The current world-record efficiency of PSCs is based on organic hole transport materials, which are usually susceptible to degradation from heat and diffusion of dopants. A simple solution would be to replace the generally used organic hole transport layers (HTLs) with a more stable inorganic material. This review article summarizes recent contributions of inorganic hole transport materials to PSC development, focusing on aspects of device performance and long-term stability. Future research directions of inorganic HTLs in the progress of PSC research and challenges still remaining will also be discussed.

Degradation of Perovskite Thin Films and Solar Cells with Candle Soot C/Ag Electrode Exposed in a Control Ambient

Perovskite solar cells (PSCs) have already achieved efficiencies of over 25%; however, their instability and degradation in the operational environment have prevented them from becoming commercially viable. Understanding the degradation mechanism, as well as improving the fabrication technique for achieving high-quality perovskite films, is crucial to overcoming these shortcomings. In this study, we investigated details in the changes of physical properties associated with the degradation and/or decomposition of perovskite films and solar cells using XRD, FESEM, EDX, UV-Vis, Hall-effect, and current-voltage (I-V) measurement techniques. The dissociation, as well as the intensity of perovskite peaks, have been observed as an impact of film degradation by humidity. The decomposition rate of perovskite film has been estimated from the structural and optical changes. The performance degradation of novel planner structure PSCs has been investigated in detail. The PSCs were fabricated in-room ambient using candle soot carbon and screen-printed Ag electrode. It was found that until the perovskite film decomposed by 30%, the film properties and cell efficiency remained stable.

Drop-Casting Method to Screen Ruddlesden-Popper Perovskite Formulations for Use in Solar Cells

Small-area metal-halide perovskite solar cells (PSCs) having power-conversion efficiencies (PCEs) of greater than 25% can be prepared by using a spin-coated perovskite layer, but this technique is not readily transferrable to large-scale manufacturing. Drop-casting is a simple alternative method for film formation that is more closely aligned to industry-relevant coating processes. In the present work, drop-casting was used to prepare films for screening two-dimensional Ruddlesden-Popper (2DRP) metal-halide perovskite formulations for potential utility in PSCs, without additional processing steps such as inert-gas blowing or application of antisolvent. The composition of the 2DRP formulation used for drop-casting was found to have a profound effect on optical, spectroscopic, morphological, and phase-distribution properties of the films as well as the photovoltaic performance of related PSC devices. This facile method for screening film quality greatly assists in speeding up the identification of perovskite formulations of interest. The optimal 2DRP perovskite formulation identified from screening was utilized for industry-relevant one-step roll-to-roll slot-die coating on a flexible plastic substrate, producing PSCs having PCEs of up to 8.8%. A mechanism describing film formation and phase distribution in the films is also proposed.

Optimizing the Aspect Ratio of Nanopatterned Mesoporous TiO2 Thin-Film Layer to Improve Energy Conversion Efficiency of Perovskite Solar Cells

The energy conversion efficiency (ECE) (η), current density (J_sc), open-circuit voltage (V_oc), and fill factor (ff) of perovskite solar cells were studied by using the transmittance of a nanopatterned mesoporous TiO₂ (mp-TiO₂) thin-film layer. To improve the ECE of perovskite solar cells, a mp-TiO₂ thin-film layer was prepared to be used as an electron transport layer (ETL) via the nanoimprinting method for nanopatterning, which was controlled by the aspect ratio. The nanopatterned mp-TiO₂ thin-film layer had a uniform and well-designed structure, and the diameter of nanopatterning was 280 nm. The aspect ratio was controlled at the depths of 75, 97, 127, and 167 nm, and the perovskite solar cell was fabricated with different depths. The ECE of the perovskite solar cells with the nanopatterned mp-TiO₂ thin-film layer was 14.50%, 15.30%, 15.83%, or 14.24%, which is higher than that of a non-nanopatterned mp-TiO₂ thin-film layer (14.07%). The enhancement of ECE was attributed to the transmittance of the nanopatterned mp-TiO₂ thin-film layer that is due to the improvement of the electron generation. As a result, better electron generation affected the electron density, and J_sc increased the V_oc, and ff of perovskite solar cells.

Simulating the Performance of a Formamidinium Based Mixed Cation Lead Halide Perovskite Solar Cell

With the aim of decreasing the number of experiments to obtain a perovskite solar cell (PSC) with maximum theoretical efficiency, in this paper, PSC performance was studied using the program solar cell capacitance simulator (SCAPS-1D). The PSC with the architecture ITO/TiO₂/perovskite/spiro-MeOTAD/Au was investigated, while the selected perovskite was mixed cation Rb_0.05Cs_0.1FA_0.85PbI₃. The analysis was based on an experimentally prepared solar cell with a power conversion efficiency of ~7%. The PSC performance, verified by short-circuit current density (J_sc), open-circuit voltage (V_oc), fill factor (FF) and power conversion efficiency (PCE), was studied by optimization of the simulation parameters responsible for improvement of the cell operation. The optimized parameters were absorber layer thickness, doping, defect concentration and the influence of the resistivity (the net effect of ohmic loss, R_s and the leakage current loss represented by the resistivity, R_shunt). The results of SCAPS-1D simulations estimated the theoretical power conversion efficiency of 15% for our material. We have showed that the main contribution to improvement of solar cell efficiency comes with lowering ohmic resistivity of the cell as well as doping and defect concentration, because their concentration is proportional to recombination rate.

A Brief Review of the Role of 2D Mxene Nanosheets toward Solar Cells Efficiency Improvement

This article discusses the application of two-dimensional metal MXenes in solar cells (SCs), which has attracted a lot of interest due to their outstanding transparency, metallic electrical conductivity, and mechanical characteristics. In addition, some application examples of MXenes as an electrode, additive, and electron/hole transport layer in perovskite solar cells are described individually, with essential research issues highlighted. Firstly, it is imperative to comprehend the conversion efficiency of solar cells and the difficulties of effectively incorporating metal MXenes into the building blocks of solar cells to improve stability and operational performance. Based on the analysis of new articles, several ideas have been generated to advance the exploration of the potential of MXene in SCs. In addition, research into other relevant MXene suitable in perovskite solar cells (PSCs) is required to enhance the relevant work. Therefore, we identify new perspectives to achieve solar cell power conversion efficiency with an excellent quality-cost ratio.

Sensitive, High-Speed, and Broadband Perovskite Photodetectors with Built-In TiO2 Metalenses

Monolithic integration of nanostructured metalenses with broadband light transmission and good charge transport can simultaneously enhance the sensitivity, speed, and efficiency of photodetectors. The realization of built-in broadband metalenses in perovskite photodetectors, however, has been largely challenged by the limited choice of materials and the difficulty in nanofabrication. Here a new type of broadband-transmitting built-in TiO₂ metalens (meta-TiO₂ ) is devised, which is readily fabricated by one-step and lithograph-free glancing angle deposition. The meta-TiO₂ , which comprises of sub-100 nm TiO₂ nanopillars randomly spaced with a wide range of sub-wavelength distances in 5-200 nm, shows high transmittance of light in the wavelength range of 400-800 nm. The meta-TiO₂ also serves as an efficient electron transporting layer to prevent the exciton recombination and facilitate the photoinduced electron extraction and transport. Replacing the conventional mesoporous TiO₂ with the meta-TiO₂ comprehensively leads to enhancing the detection speed by three orders of magnitude to a few hundred nanoseconds, improving the responsivity and detectivity by one order of magnitude to 0.5 A W^-1 and 10¹³ Jones, respectively, and extending the linear dynamic range by 50% to 120 dB.

Achieving Band Gap Reduction and Carrier Lifetime Enhancement in Metal Halide Perovskites via Mechanical Stretching

Strain engineering has become an efficient way to tune the optical and electronic behaviors of metal halide perovskites as a result of their unique structure-dependent optoelectronic characteristics. In this work, we show that the band gap can be reduced and, meanwhile, the carrier lifetime is increased by simply stretching the MAPbI_3-xCl_x perovskite thin films. The narrowed band gap and prolonged carrier lifetime are beneficial for the photovoltaic actions, indicating that mechanical stretching can be a simple and efficient way to achieve photovoltaic property optimization of stretchable perovskite-based devices. Furthermore, Raman spectra show that the Pb-I bond length is shortened with mechanical stretching, which increases the valence band maximum (VBM) through orbital coupling, leading to a narrower band gap. Consequently, the trap states near VBM can be radiative as the trap energy levels become closer to the VBM, resulting in a prolonged carrier lifetime. This work brings huge opportunities to control the optoelectronic properties of metal halide perovskites through mechanical stress toward optoelectronic applications.

Light-Emitting 0D Hybrid Metal Halide (C3H12N2)2Sb2Cl10 with Antimony Dimers

Low-dimensional organic-inorganic metal halides (OIMHs), as emerging light-emitting materials, have aroused widespread attention owing to their unique structural tunability and photoelectric characteristics. OIMHs are also promising materials for optoelectronic equipment, light-emitting diodes, and photodetectors. In this study, (C₃H₁₂N₂)₂Sb₂Cl₁₀ (C₃H₁₂N₂²⁺ is an N-methylethylenediamine cation), a new zero-dimensional OIMH, has been reported, and (C₃H₁₂N₂)₂Sb₂Cl₁₀ possesses a P2₁/n space group. The (C₃H₁₂N₂)₂Sb₂Cl₁₀ structure contains [Sb₂Cl₁₀]^4- dimers (composed of two edge-sharing [SbCl₆]^3- octahedra) that are surrounded by C₃H₁₂N₂²⁺ cations. The experimental band gap of (C₃H₁₂N₂)₂Sb₂Cl₁₀ is 3.80 eV, and density functional theory calculation demonstrates that (C₃H₁₂N₂)₂Sb₂Cl₁₀ possesses a direct band gap, with the edge of the band gap mainly contributed from the inorganic units. (C₃H₁₂N₂)₂Sb₂Cl₁₀ exhibits good ambient and thermal stability. Under 395 nm excitation at room temperature, (C₃H₁₂N₂)₂Sb₂Cl₁₀ exhibits a broad emission with a full width at half-maximum of ∼114 nm, peaking at 480 nm, and the broad emission was ascribed to self-trapped exciton emission.

Creating a Dual-Functional 2D Perovskite Layer at the Interface to Enhance the Performance of Flexible Perovskite Solar Cells

Flexible perovskite solar cells (f-PSCs) have been attracting tremendous attention due to their potentially commercial prospects in flexible energy system and mobile energy system. Reducing the energy barriers and charge extraction losses at the interfaces between perovskite and charge transport layers is essential to improve both efficiency and stability of f-PSCs. Herein, 4-trifluoromethylphenylethylamine iodide (CF₃ PEAI) is introduced to form a 2D perovskite at the interface between perovskite and hole transport layer (HTL). It is found that the 2D perovskite plays a dual-functional role in aligning energy band between perovskite and HTL and passivating the traps in the 3D perovskite, thus reducing energy loss and charge carrier recombination at the interface, facilitating the hole transfer from perovskite to the Spiro-OMeTAD. Consequently, the photovoltaic performance of f-PSCs is significantly improved, leading to a power conversion efficiency (PCE) of 21.1% and a certified PCE of 20.5%. Furthermore, the long-term stability of f-PSCs is greatly improved through the protection of 2D perovskite layer to the underlying 3D perovskite. This work provides an excellent strategy to produce efficient and stable f-PSCs, which will accelerate their potential applications.

Mitigation of vacancy with ammonium salt-trapped ZIF-8 capsules for stable perovskite solar cells through simultaneous compensation and loss inhibition

Due to the easy loss of ions during synthesis or usage, vacancies in perovskite film are ubiquitous, accelerating the degradation of perovskite materials and seriously hampering the stability of perovskite solar cells (PSCs). Herein, to simultaneously compensate for vacancies and reduce ammonium cation loss, a sustained release strategy was proposed by introducing multi-functional capsules consisting of zeolitic imidazolate framework-8 (ZIF-8) encapsulation agent and ammonium iodide salts as interlayer between the perovskite and hole transport layer. In the capsule interlayer, not only are ammonium iodide salts in ZIF-8 pores released to the perovskite layer, compensating for the vacancies, but the ZIF-8 also prevents the organic component of perovskite from evaporating and isolates the perovskite from moisture. As a consequence, decreased trap density, improved device efficiency, and enhanced stability of PSCs are obtained owing to the successful passivation of defects by the introduced capsules. ZIF-8@FAI shows the highest efficiency of 19.13% and a stabilized PCE over 93% of the initial efficiency at maximum power point for 150 h. This work provides a new strategy to improve efficiency and stability of PSCs based on the large family of porous materials.

Functionalized Ionic Liquid-Crystal Additive for Perovskite Solar Cells with High Efficiency and Excellent Moisture Stability

Organic-inorganic hybrid perovskite solar cells (PSCs) have emerged as a promising candidate for next-generation solar cells. However, the limited stability of PSCs hampers their practical applications. In this work, for the first time, a functionalized π-conjugated ionic liquid crystal (ILC), 4'-(N,N,N-trimethyl ammonium bromide hexyloxy)-4-cyanobiphenyl (6CNBP-N), is developed as a novel chemical additive to obtain CH₃NH₃PbI₃ (MAPbI₃) PSCs with high efficiency and excellent moisture stability. This 6CNBP-N ILC possesses the characteristics of ionic liquids and liquid crystals. The inclusion of the 6CNBP-N ILC can effectively improve the quality and stability of perovskite films, reduce the trap-state densities, and promote the carrier transport induced by the cyano group (C≡N), a rod-like π-conjugated biphenyl mesogenic unit and quaternary alkylammonium cations (R₄N⁺) in 6CNBP-N. Through this functionalized ILC engineering strategy, the power conversion efficiency (PCE) of PSCs is greatly increased from 18.07% for the control PSC to 20.45% for the PSC with 6CNBP-N along with the depressed hysteresis effect and enhanced moisture stability of PSCs. Our work provides a new strategy for designing functionalized additives for high-performance PSCs.

Perovskite-based tandem solar cells

The power conversion efficiency for single-junction solar cells is limited by the Shockley-Quiesser limit. An effective approach to realize high efficiency is to develop multi-junction cells. These years have witnessed the rapid development of organic-inorganic perovskite solar cells. The excellent optoelectronic properties and tunable bandgaps of perovskite materials make them potential candidates for developing tandem solar cells, by combining with silicon, Cu(In,Ga)Se₂ and organic solar cells. In this review, we present the recent progress of perovskite-based tandem solar cells, including perovskite/silicon, perovskite/perovskite, perovskite/Cu(In,Ga)Se₂, and perovskite/organic cells. Finally, the challenges and opportunities for perovskite-based tandem solar cells are discussed.