Perovskite-based tandem solar cells

Inhomogeneous Halide Anions Distribution along Out-of-Plane Direction in Wide-Bandgap Perovskite Solar Cells and Its Effect on Open Circuit Voltage Loss and Phase Segregation

The large open circuit voltage (VOC) loss and phase segregation are two main obstacles hindering the development of wide-bandgap perovskite solar cells (PSCs). Even though substantial progress has been made through crystallization regulation and surface modification on perovskite, the mechanism of VOC loss and phase segregation has rarely been studied. In this paper, we first investigate the halide ions distribution along the out-of-plane direction and find the initial inhomogeneous distribution of halide ions during the crystallization process is an important reason. It leads to the formation of an unfavorable potential well in PSCs, resulting in VOC loss as well as generation of strong strain exacerbating phase segregation. Through introducing melatonin (MT) into perovskite precursors, a homogeneous distribution of halide anions is realized due to the well-regulated crystallization. Consequently, the treated PSCs exhibit an optimized power conversion efficiency (PCE) of 22.88% with a VOC loss as low as 0.38 V, which are the best values for wide-bandgap PSCs up to now.

Surface Energy-Assisted Patterning of Vapor Deposited All-Inorganic Perovskite Arrays for Wearable Optoelectronics

Solution-based methods for fabricating all-inorganic perovskite film arrays often suffer from limited control over nucleation and crystallization, resulting in poor homogeneity and coverage. To improve film quality, advanced vapor deposition techniques are employed for continuous film. Here, the vapor deposition strategy to the all-inorganic perovskite films array, enabling area-selective deposition of perovskite through substrate modulation is expanded. It can yield a high-quality perovskite film array with different pixel shapes, various perovskite compositions, and a high resolution of 423 dpi. The resulting photodetector arrays exhibit remarkable optoelectronic performance with an on/off ratio of 13 887 and responsivity of 47.5 A W-1. The device also displays long-term stability in a damp condition for up to 12 h. Moreover, a pulse monitoring sensor based on the perovskite films array demonstrates stable monitoring for pulse signals after being worn for 12 h and with a low illumination of 0.055 mW cm-2, highlighting the potential application in wearable optoelectronic devices.

Limitations and Progresses in Carbon-Based Cesium Lead Halide Perovskite Solar Cells

Inorganic cesium lead halide perovskites (CsPbIxBr3-x, 0≤x≤3) are promising alternatives with great thermal stability. Additionally, the choice of moisture-resistive and dopant-free carbon as the electrode material can simultaneously solve the problems of stability and cost. Therefore, carbon electrode-based inorganic PSCs (C-IPSCs) represent a promising candidate for commercialization, yet both the efficiencies and stability of related devices demand further progress. This article reviews the recent advancement of C-IPSCs and then unravels the distinctive merits and limitations in this field. Subsequently, our perspective on various modification strategies is analyzed on a methodological level. Finally, this article outlooks the promising research contents and the remaining unresolved issues in this field. We believe that understanding and analyzing the related problems in this field are instructive to stimulate the future development of C-IPSCs.

Visualizing the Structure-Property Nexus of Wide-Bandgap Perovskite Solar Cells under Thermal Stress

Wide-bandgap perovskite solar cells (PSCs) toward tandem photovoltaic applications are confronted with the challenge of device thermal stability, which motivates to figure out a thorough cognition of wide-bandgap PSCs under thermal stress, using in situ atomic-resolved transmission electron microscopy (TEM) tools combing with photovoltaic performance characterizations of these devices. The in situ dynamic process of morphology-dependent defects formation at initial thermal stage and their proliferations in perovskites as the temperature increased are captured. Meanwhile, considerable iodine enables to diffuse into the hole-transport-layer along the damaged perovskite surface, which significantly degrade device performance and stability. With more intense thermal treatment, atomistic phase transition reveals the perovskite transform to PbI2 along the topo-coherent interface of PbI2/perovskite. In conjunction with density functional theory calculations, a mutual inducement mechanism of perovskite surface damage and iodide diffusion is proposed to account for the structure-property nexus of wide-bandgap PSCs under thermal stress. The entire interpretation also guided to develop a thermal-stable monolithic perovskite/silicon tandem solar cell.

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.

Anti-Solvent-Free Preparation for Efficient and Photostable Pure-Iodide Wide-Bandgap Perovskite Solar Cells

The perovskite/silicon tandem solar cell (TSC) has attracted tremendous attention due to its potential to breakthrough the theoretical efficiency set for single-junction solar cells. However, the perovskite solar cell (PSC) designed as its top component cell suffers from severe photo-induced halide segregation owing to its mixed-halide strategy for achieving desirable wide-bandgap (1.68 eV). Developing pure-iodide wide-bandgap perovskites is a promising route to fabricate photostable perovskite/silicon TSCs. Here, we report efficient and photostable pure-iodide wide-bandgap PSCs made from an anti-solvent-free (ASF) technique. The ASF process is achieved by mixing two precursor solutions, both of which are capable of depositing corresponding perovskite films without involving anti-solvent. The mixed solution finally forms Cs0.3DMA0.2MA0.5PbI3 perovskite film with a bandgap of 1.68 eV. Furthermore, methylammonium chloride additive is applied to enhance the crystallinity and reduce the trap density of perovskite films. As a result, the pure-iodide wide-bandgap PSC delivers efficiency as high as 21.30 % with excellent photostability, the highest for this type of solar cells. The ASF method significantly improves the device reproducibility as compared with devices made from other anti-solvent methods. Our findings provide a novel recipe to prepare efficient and photostable wide-bandgap PSCs.

Interface Engineering for Highly Efficient Organic Solar Cells

Organic solar cells (OSCs) have made dramatic advancements during the past decades owing to the innovative material design and device structure optimization, with power conversion efficiencies surpassing 19% and 20% for single-junction and tandem devices, respectively. Interface engineering, by modifying interface properties between different layers for OSCs, has become a vital part to promote the device efficiency. It is essential to elucidate the intrinsic working mechanism of interface layers, as well as the related physical and chemical processes that manipulate device performance and long-term stability. In this article, the advances in interface engineering aimed to pursue high-performance OSCs are reviewed. The specific functions and corresponding design principles of interface layers are summarized first. Then, the anode interface layer, cathode interface layer in single-junction OSCs, and interconnecting layer of tandem devices are discussed in separate categories, and the interface engineering-related improvements on device efficiency and stability are analyzed. Finally, the challenges and prospects associated with application of interface engineering are discussed with the emphasis on large-area, high-performance, and low-cost device manufacturing.

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.

Enhancement in the Efficiency of Sb2 Se3 Solar Cells by Triple Function of Lithium Hydroxide Modified at the Back Contact Interface

The efficiency of antimony selenide (Sb2 Se3 ) solar cells is still limited by significant interface and deep-level defects, in addition to carrier recombination at the back contact surface. This paper investigates the use of lithium (Li) ions as dopant for Sb2 Se3 films, using lithium hydroxide (LiOH) as a dopant medium. Surprisingly, the LiOH solution not only reacts at the back surface of the Sb2 Se3 film but also penetrate inside the film along the (Sb4 Se6 )n molecular chain. First, the Li ions modify the grain boundary's carrier type and create an electric field between p-type grain interiors and n-type grain boundary. Second, a gradient band structure is formed along the vertical direction with the diffusion of Li ions. Third, carrier collection and transport are improved at the surface between Sb2 Se3 and the Au layer due to the reaction between the film and alkaline solution. Additionally, the diffusion of Li ions increases the crystallinity, orientation, surface evenness, and optical electricity. Ultimately, the efficiency of Sb2 Se3 solar cells is improved to 7.57% due to the enhanced carrier extraction, transport, and collection, as well as the reduction of carrier recombination and deep defect density. This efficiency is also a record for CdS/Sb2 Se3 solar cells fabricated by rapid thermal evaporation.

Outstanding conversion efficiency of 38.39% from a Perovskite/CIGS tandem PV cell: A synergic optimization through computational modeling

An all-inorganic lead-free tandem PV cell consisting of two sub-cells CsSn0.5Ge0.5I3 (perovskite) based top cell/CIGS-based bottom cell has been designed, simulated, and optimized by varying the thickness of pertinent layers utilizing the SCAPS-1D simulator. In the top sub-cell, a wide bandgap lead-free inorganic CsSn0.5Ge0.5I3 perovskite is inserted as the primary absorber layer because of its distinctive characteristics with an ETL of ZnO, which is recognized for its high electron mobility & absorption coefficient, and an HTL of NiO to offer increased hole mobility with good chemical-durability. For the bottom sub-cell, we have selected p-type CIGS as the absorber with Spiro-OMeTAD as the apposite HTL to provide suitable offsets of valence and conduction band distribution and TiO2 as ETL to offer low-cost, low-ecotoxicity, excellent optical properties, and chemical-stability and thus offers improved efficiency of the overall tandem structure. In the beginning, the two sub-cells were simulated independently; the top sub-cell was simulated under the standard spectrum of AM1.5G, while the bottom sub-cell was optimized using a filtered spectrum. Thereafter, the current matching point of both cells was attained by optimizing the absorber layer thicknesses. Finally, our computational modeling and simulation results offer the optimized cell structure revealing an outstanding overall 38.39% power conversion efficiency (PCE), Fill Factor (FF) of 83.4%, open-circuit voltage (V O C ) of 2.48 V, and short-circuit current density (J s c ) of 18.64 mA cm-2. The proposed tandem structure's performance matrices outperform those stated in the most recent literature. These outcomes of the proposed structure are expected to facilitate the development and production of a low-cost and highly effective inorganic perovskite Tandem PV cell in the future.

Bifacial and Semitransparent Sb2 (S,Se)3 Solar Cells for Single-Junction and Tandem Photovoltaic Applications

Thin-film solar cells are expected to play a significant role in the space industry, building integrated photovoltaic (BIPV), indoor applications, and tandem solar cells, where bifaciality and semitransparency are highly desired. Sb2 (S,Se)3 has emerged as a promising new photovoltaic (PV) material for its high absorption coefficient, tunable bandgap, and nontoxic and earth-abundant constituents. However, high-efficiency Sb2 (S,Se)3 solar cells exclusively employ monofacial architectures, leaving a considerable gap toward large-scale application in aforementioned fields. Here, a bifacial and semitransparent Sb2 (S,Se)3 solar cell and its extended application in tandem solar cells are reported. The transparent conductive oxides (TCOs) and the ultrathin inner n-i-p structure provide high long-wavelength transmittance. Despite the MnS/ITO Schottky junction, power conversion efficiencies (PCEs) of 7.41% and 6.36% are achieved with front and rear illumination, respectively, contributing to a great bifaciality of 0.86. Consequently, the reported device gains great enhancement in PV performance by exploiting albedo of surroundings and shows exceptional capability in absorbing tilt incident light. Moreover, an Sb2 (S,Se)3 /Si tandem solar cell with a PCE of 11.66% is achieved in preliminary trials. These exciting findings imply that bifacial and semitransparent Sb2 (S,Se)3 solar cells possess tremendous potential in practical applications based on their unique characteristics.

Pure-Phase, Large-Grained Wide-Band-Gap Perovskite Films for High-Efficiency, Four-Terminal Perovskite/Silicon Tandem Solar Cells

High-quality, stable perovskite films with a wide band gap between 1.65 and 1.80 eV are highly suitable for efficient and cost-competitive silicon-based tandem solar cells. Herein, we demonstrate that the combined strategies of the Pb(SCN)2 additive and air annealing can enable the Cs0.22FA0.78Pb(I0.85Br0.15)3 films with a wide band gap of 1.65 eV and favored properties including pure composition, high crystallinity, micro-sized grains, and reduced defects. With these desired films, the average efficiencies of semitransparent perovskite solar cells (PSCs) are boosted from (18.13 ± 0.31) to (20.35 ± 0.28)%. Further, the semitransparent PSC is used to assemble the four-terminal perovskite/TOPCon tandem solar cell. Benefiting from its excellent performance and preferred optical properties, the obtained tandem solar cell yields a milestone efficiency of 30.32%.

Graded Heterojunction Improves Wide-Bandgap Perovskite for Highly Efficient 4-Terminal Perovskite/Silicon Tandem Solar Cells

Wide-bandgap (WBG) perovskite solar cells (PSCs) are essential for highly efficient and stable silicon/perovskite tandem solar cells. In this study, we adopted a synthetic strategy with lead thiocyanate (Pb(SCN)₂) additive and methylammonium chloride (MACl) posttreatment to enhance the crystallinity and improve the interface of WBG perovskite films with a bandgap of 1.68 eV. The excessive PbI₂ was formed at grain boundaries and converted into MAPbI_3-xCl_x perovskites, which are utilized to form the graded heterojunction (GHJ) and compressive strain. This is beneficial for passivating nonradiative recombination defects, suppressing halide phase segregation, and facilitating carrier extraction. Subsequently, the device with GHJ delivered a champion efficiency of 20.30% and superior stability in ambient air and under 85 °C. Finally, we achieved a recorded efficiency of 30.91% for 4-terminal WBG perovskite/TOPCon tandem silicon solar cells. Our findings demonstrate a promising approach for fabricating efficient and stable WBG PSCs through the formation of GHJ.

Influence of Component Properties on the Photovoltaic Performance of Monolithic Perovskite/Organic Tandem Solar Cells: Sub-Cell, Interconnecting Layer, and Photovoltaic Parameters

Wide-bandgap perovskite sub-cells (WPSCs)-based tandem solar cells attract considerable interest because of their capability to surpass the Shockley-Queisser limit. Monolithic perovskite/organic tandem solar cells (POTSCs) integrating WPSCs and small-bandgap organic sub-cells (SOSCs) are famous compositions owing to their simple fabrication method and compatibility with flexible devices. Most studies on POTSCs focus on enhancing device efficiency by modifying one or two of the device components (WPSCs, SOSCs, and interconnecting layers). The characteristics of POTSCs are not extensively investigated so far, especially in terms of the influence of the device structure and component properties on the tandem device photovoltaic performance. In this study, the existing p-i-n type WPSC-based p-i-n POTSCs and n-i-p type WPSC-based n-i-p POTSCs are reviewed and their advantages and limitations are highlighted. Furthermore, the influence of the tandem device component properties (optical, electrical, and photovoltaic properties) on the photovoltaic parameters (open-circuit voltage, short-circuit current density, fill factor, and power conversion efficiency) and the existing device modification methods are discussed to provide comprehensive guidance for the development of POTSCs.

Recent Advances in Wide-Bandgap Organic-Inorganic Halide Perovskite Solar Cells and Tandem Application

Perovskite-based tandem solar cells have attracted increasing interest because of its great potential to surpass the Shockley-Queisser limit set for single-junction solar cells. In the tandem architectures, the wide-bandgap (WBG) perovskites act as the front absorber to offer higher open-circuit voltage (VOC) for reduced thermalization losses. Taking advantage of tunable bandgap of the perovskite materials, the WBG perovskites can be easily obtained by substituting halide iodine with bromine, and substituting organic ions FA and MA with Cs. To date, the most concerned issues for the WBG perovskite solar cells (PSCs) are huge VOC deficit and severe photo-induced phase separation. Reducing VOC loss and improving photostability of the WBG PSCs are crucial for further efficiency breakthrough. Recently, scientists have made great efforts to overcome these key issues with tremendous progresses. In this review, we first summarize the recent progress of WBG perovskites from the aspects of compositions, additives, charge transport layers, interfaces and preparation methods. The key factors affecting efficiency and stability are then carefully discussed, which would provide decent guidance to develop highly efficient and stable WBG PSCs for tandem application.

Wide-Bandgap Perovskite Solar Cell Using a Fluoride-Assisted Surface Gradient Passivation Strategy

Wide-band gap (1.68 eV) perovskite solar cells (PSCs) are important components of perovskite/Si tandem devices. However, the efficiency of wide band gap PSCs has been limited by their huge open-circuit voltage (V_oc ) deficit due to non-radiative recombination. Deep-level acceptor defects are identified as the major killers of V_oc , and they can be effectively improved by passivation with ammonium salts. Theoretical calculation predicts that increasing the distance between F and -NH₃ ⁺ of fluorinated ammonium can dramatically enhance the electropositivity of -NH₃ ⁺ terminals, thus providing strong adsorption onto the negatively charged I_A and I_Pb anti-site defects. Characterizations further confirm that surface gradient passivation employing p-FPEAI demonstrates the most efficient passivation effect. Consequently, a record-efficiency of 21.63 % with the smallest V_oc deficit of 441 mV is achieved for 1.68 eV-band gap inverted PSCs. Additionally, a flexible PSC and 1 cm² opaque device also deliver the highest PCEs of 21.02 % and 19.31 %, respectively.

Dopant-Free Polymer Hole Transport Materials for Highly Stable and Efficient CsPbI3 Perovskite Solar Cells

All-inorganic perovskite CsPbI₃ contains no volatile organic components and is a thermally stable photoactive material for wide-bandgap perovskite solar cells (PSCs); however, CsPbI₃ readily undergoes undesirable phase transitions due to the hygroscopic nature of the ionic dopants used in commonly used hole transport materials. In the current study, the popular donor material PM6 in organic solar cells is used as a hole transport layer (HTL). The benzodithiophene-based backbone-conjugated polymer requires no dopant and leads to a higher power conversion efficiency (PCE) than 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD). Moreover, PM6 also shows priorities in hole mobility, hydrophobicity, cascade energy level alignment, and even defect passivation of perovskite films. With PM6 as the dopant-free HTL, the PSCs achieve a champion PCE of 18.27% with a competitive fill factor of 82.8%. Notably, the present PCE is based on the dopant-free HTL in CsPbI₃ PSCs reported thus far. The PSCs with PM6 as the HTL retain over 90% of the initial PCE stored in a glovebox filled with N₂ for 3000 h. In contrast, the PSCs with Spiro-OMeTAD as the HTL maintain ≈80% of the initial PCE under the same conditions.

Cerium-Doped Indium Oxide as a Top Electrode of Semitransparent Perovskite Solar Cells

Semitransparent perovskite solar cells (ST-PSCs) play a very important role in high-efficiency tandem solar cells and building integrated photovoltaics (BIPV). One of the main challenges for high-performance ST-PSCs is to obtain suitable top-transparent electrodes by appropriate methods. Transparent conductive oxide (TCO) films, as the most widely used transparent electrodes, are also adopted in ST-PSCs. However, the possible ion bombardment damage during the TCO deposition and the relatively high postannealing temperature usually required for high-quality TCO films is not conducive to improving the performance of the perovskite solar cells with low ion bombardment and temperature tolerances. Herein, cerium-doped indium oxide (ICO) thin films are prepared by reactive plasma deposition (RPD) at substrate temperatures below 60 °C. A high carrier mobility of 50.26 cm² V^-1 s^-1, a low resistivity of 7.18 × 10^-4 Ω·cm, and an average transmittance of 86.53% in the wavelength range of 400-800 nm and 87.37% in the wavelength range of 800-1200 nm are achieved. The RPD-prepared ICO film is used as a transparent electrode on top of the ST-PSCs (band gap ∼1.68 eV), and photovoltaic conversion efficiency (PCE) of 18.96% is achieved on the champion device.

Design and optimization of four-terminal mechanically stacked and optically coupled silicon/perovskite tandem solar cells with over 28% efficiency

Silicon/perovskite tandem devices are believed to be a favorite contender for improving cell performance over the theoretical maximum value of single-junction photovoltaic (PV) cells. The present study evaluates the design and optimization of four-terminal (4-T) mechanically stacked and optically coupled configurations using SCAPS (solar cell capacitance simulator). Low-cost, stable, and easily processed semitransparent carbon electrode-based perovskite solar cells (c-PSCs) without hole transport material (HTM) and highly efficient crystalline silicon (c-Si) PV cells were utilized as top and bottom cells, respectively. The wide bandgap multi-cation perovskite C s x ( F A 0.4 M A 0.6 ) 1 - x P b I 2.8 B r 0.2 and a low bandgap c-Si were employed as light-harvesting layers in the top and bottom cells, respectively. The impact of perovskite thickness and doping concentrations were examined and optimized for both tandem configurations. Under optimized conditions, thicknesses of 1000 nm and 1100 nm are the best values of the perovskite absorber layer for 4-T mechanically stacked and optically coupled arrangements, respectively. Likewise, 1 × 10¹⁷ cm^-3 doping concentration of top cells revealed the highest performance in both structures. With these optimized parameters under tandem configurations, efficiency values of 28.38% and 29.34% were obtained in 4-T mechanically and optically coupled tandems, respectively. Results suggest that by optimizing perovskite thickness and doping concentration, the proposed designs using HTM-free c-PSCs could enhance device performance.

4-Terminal Inorganic Perovskite/Organic Tandem Solar Cells Offer 22% Efficiency

After fast developing of single-junction perovskite solar cells and organic solar cells in the past 10 years, it is becoming harder and harder to improve their power conversion efficiencies. Tandem solar cells are receiving more and more attention because they have much higher theoretical efficiency than single-junction solar cells. Good device performance has been achieved for perovskite/silicon and perovskite/perovskite tandem solar cells, including 2-terminal and 4-terminal structures. However, very few studies have been done about 4-terminal inorganic perovskite/organic tandem solar cells. In this work, semi-transparent inorganic perovskite solar cells and organic solar cells are used to fabricate 4-terminal inorganic perovskite/organic tandem solar cells, achieving a power conversion efficiency of 21.25% for the tandem cells with spin-coated perovskite layer. By using drop-coating instead of spin-coating to make the inorganic perovskite films, 4-terminal tandem cells with an efficiency of 22.34% are made. The efficiency is higher than the reported 2-terminal and 4-terminal inorganic perovskite/organic tandem solar cells. In addition, equivalent 2-terminal tandem solar cells were fabricated by connecting the sub-cells in series. The stability of organic solar cells under continuous illumination is improved by using semi-transparent perovskite solar cells as filter.

Monovalent Copper Cation Doping Enables High-Performance CsPbIBr2-Based All-Inorganic Perovskite Solar Cells

Organic-inorganic perovskite solar cells (PSCs) have delivered the highest power conversion efficiency (PCE) of 25.7% currently, but they are unfortunately limited by several key issues, such as inferior humid and thermal stability, significantly retarding their widespread application. To tackle the instability issue, all-inorganic PSCs have attracted increasing interest due to superior structural, humid and high-temperature stability to their organic-inorganic counterparts. Nevertheless, all-inorganic PSCs with typical CsPbIBr₂ perovskite as light absorbers suffer from much inferior PCEs to those of organic-inorganic PSCs. Functional doping is regarded as a simple and useful strategy to improve the PCEs of CsPbIBr₂-based all-inorganic PSCs. Herein, we report a monovalent copper cation (Cu⁺)-doping strategy to boost the performance of CsPbIBr₂-based PSCs by increasing the grain sizes and improving the CsPbIBr₂ film quality, reducing the defect density, inhibiting the carrier recombination and constructing proper energy level alignment. Consequently, the device with optimized Cu⁺-doping concentration generates a much better PCE of 9.11% than the pristine cell (7.24%). Moreover, the Cu⁺ doping also remarkably enhances the humid and thermal durability of CsPbIBr₂-based PSCs with suppressed hysteresis. The current study provides a simple and useful strategy to enhance the PCE and the durability of CsPbIBr₂-based PSCs, which can promote the practical application of perovskite photovoltaics.

Application of porosities in the transparent electrode layer of a perovskite solar cell for performance enhancement

Substitution of monocrystalline or polycrystalline silicon as active materials in photovoltaics with highly efficient perovskite materials is quite common. Although perovskite materials offer better flexibility, are cost-effective, and have higher conversion efficiency, they still require structural modifications for better performance. This study quantitatively investigates how mesoporous top surfaces improve the performance of methylammonium lead iodide (C H ₃ N H ₃ P b I ₃) perovskite solar cells. In fact, both the diameter and the depth of the pores have been tuned to achieve better performance. The performance is further optimized by replacing mesoporous active material with planar active material coated with mesoporous indium tin oxide (ITO). We have demonstrated that the proposed structure achieves the maximum conversion efficiency (η) of 27.43% with an open-circuit voltage (V _{O C} ) of 1.07 V and a short circuit current density (J _{S C} ) of 29.09m A/c m ², with a fill factor (FF) of 88.10%.

Improvement Strategies for Stability and Efficiency of Perovskite Solar Cells

Recently, perovskites have garnered great attention owing to their outstanding characteristics, such as tunable bandgap, rapid absorption reaction, low cost and solution-based processing, leading to the development of high-quality and low-cost photovoltaic devices. However, the key challenges, such as stability, large-area processing, and toxicity, hinder the commercialization of perovskite solar cells (PSCs). In recent years, several studies have been carried out to overcome these issues and realize the commercialization of PSCs. Herein, the stability and photovoltaic efficiency improvement strategies of perovskite solar cells are briefly summarized from several directions, such as precursor doping, selection of hole/electron transport layer, tandem solar cell structure, and graphene-based PSCs. According to reference and analysis, we present our perspective on the future research directions and challenges of PSCs.

High-Performance 1 cm2 Perovskite-Organic Tandem Solar Cells with a Solvent-Resistant and Thickness-Insensitive Interconnecting Layer

Organic solar cells (OSCs) and perovskite solar cells (PVSCs) are promising candidates for next-generation thin film photovoltaic technologies. The integration of OSCs with PVSCs in tandem devices is now attracting significant attention due to their similar fabrication procedures and the potential to afford a higher device performance. Here, a thickness-insensitive and solvent-resistant interconnecting layer is developed to efficiently connect perovskite and organic subcells with low contact resistance. The resultant perovskite-organic tandem devices maintain high efficiencies over a wide thickness range of the interconnecting layer, from ∼20 nm to ∼50 nm, providing an easily fabricated, solvent-resistant platform to integrate perovskite and organic active layers with low-temperature solution processing techniques. The tandem devices containing an ultrathin PVSC and a typical non-fullerene OSC give a maximum efficiency of 19.2%, which is much higher than those of the single-junction devices. Moreover, highly reproducible 1 cm² perovskite-organic tandem devices are achieved using the thickness-insensitive and solvent-resistant interconnecting layer, and an efficiency of 17.8% is realized. These 1 cm² tandem solar cells are used successfully in solar-to-hydrogen systems to afford a solar-to-fuel conversion efficiency of 11.2%. Overall, these advances represent significant progress in the design of ultrathin and facile solution processed perovskite-organic tandem solar cells.

High-Efficiency p-n Homojunction Perovskite and CIGS Tandem Solar Cell

Efficiency has been known to be one of the most important factors in a solar cell. This article presents the results of a simulation performed on a perovskite/CIGS dual-junction solar cell. In this report, first, a top solar cell consisting of a perovskite absorber layer is simulated using the pn-junction; the separation and transfer of carriers in this structure are done by the internal electric field. The pn-junction has a discharge area smaller than the pin-junction, which increases carrier recombination and reduces optical losses. The perovskite band gap of 1.9 eV is considered, and the efficiency is 21.65% using the Au electrode. Then, the bottom solar cell is fabricated with a CIGS absorbent layer with a 1.4 eV band gap and an efficiency of 11.46%. After simulating and evaluating the performance of the top and bottom solar cells independently, both cells were simulated and examined for the dual-junction state. Since the perovskite and CIGS band gaps are both adjustable, these two materials can act as a proper partner for an absorbent layer in a dual-junction solar cell. In this structure, instead of the usual connection of p-i-n and n-i-p perovskite, n-type and p-type homojunction perovskite connection is used, in which the transfer and separation of carriers are done by an internal electric field. Due to the fact that in this structure, the discharge area is smaller, the recombination of carriers is increased, and the light losses are reduced, which will increase the absorption and efficiency of the cell. The results show that in the tandem design, we encounter an increase in Voc (2.25 V), thus increasing the efficiency of the solar cell (30.71%).

Investigation of optical and electrical properties of novel 4T all perovskite tandem solar cell

In this paper, a combined three-dimensional (3D) optical-electrical simulation of non-pb and flexible four-terminal (4T) all perovskite tandem solar cell (APTSC) is presented. In this structure, polyethylene terephthalate (PET) is used as substrates, while the top sub cell has a [Formula: see text] absorber layer and the bottom sub cell has a [Formula: see text] absorber layer. This structure is used as a reference in this paper and the optical and electrical properties of it are investigated using the finite element method (FEM). It is shown that this structure has a total power conversion efficiency (PCE) of [Formula: see text]. Then, the elimination of the buffer layer and the addition of antireflection layer (ARL) strategies, as well as the use of periodic nano-texture patterns, are used to increase the reference structure's total PCE. A free-buffer layer tandem device is presented to minimize the parasitic absorption. While the total PCE is improved by [Formula: see text] in this case, one of the fabrication steps is also eliminated. A plasma-polymer-fluorocarbon (PPFC) coating layer is suggested as ARL on the substrates of both sub cells to reduce reflection loss. With optimized these layers thickness, total PCE is increased by [Formula: see text]. Because the PPFC layer is hydrophobic, the top surface of two sub cells in this structure has self-cleaning characteristic. As a result, this device offers long-term moisture resistance. Finally, the best structure in terms of the maximum total PCE is presented by increasing optical path-length utilizing nano-photonic and nano-plasmonic structures. The final structure is offered as a 4T tandem solar cell (TSC) that is environmentally friendly, extremely flexible, and has self-cleaning capability, with a total PCE of [Formula: see text], which is greater than the total PCE of the reference structure by [Formula: see text].

Two-dimensional InSb/GaAs- and InSb/InP-based tandem photovoltaic device with matched bandgap

The past several years have witnessed remarkable research efforts to develop high-performance photovoltaics (PVs), to curtail the energy crisis by avoiding dependence on traditional fossil fuels. In this regard, there is an urgent need to accelerate research progress on new low-dimensional semiconductors with superior electronic and optical properties. Herein, combining abundant related PV experimental data in the literature and our systematic theoretical calculations, we propose two-dimensional (2D) InSb/GaAs and InSb/InP-based tandem PVs with high solar-to-electric efficiency up to near 30.0%. Firstly, according to first-principles calculations, the stability, electronic and optical properties of single-layer group-III-V materials (XY, X = Ga and In, Y = N, P, As, Sb, and Bi) are systematically introduced. Next, due to the high bandgap (E_g) of GaAs and InP being a perfect match with the low E_g of InSb, InSb/GaAs- and InSb/InP-based tandem PVs are constructed. In addition, the complementary absorption spectra of these two subcells can facilitate the achievement of high tandem power conversion efficiency. Furthermore, we have analyzed in detail the influencing factors for PCE and the physical mechanism of the optimized match between the top and bottom subcells in the tandem configurations. Our designed 2D-semiconductor-based PVs can be expected to bring a new perspective for future commercialized high-efficiency energy devices.

Toward stable lead halide perovskite solar cells: A knob on the A/X sites components

Hybrid lead halide ABX3 perovskite solar cells (PSCs) have emerged as a strong competitor to the traditional solar cells with a certified power conversion efficiency beyond 25% and other remarkable features such as light weight, solution processability, and low manufacturing cost. Further development on the efficiency and stability brings forth increasing attention in the component regulation, such as partial or entire substitution of A/B/X sites by alternative elements with similar size. However, the relationships between composition, property, and performance are poorly understood. Here, the instability of PSCs from the photon-, moisture-, thermal-, and mechanical-induced degradation was first summarized and discussed. In addition, the component regulation from the A/X sites is highlighted from the aspects of band level alignment, charge-carrier dynamics, ion migration, crystallization behavior, residual strain, stoichiometry, and dimensionality control. Finally, the perspectives and future outlooks are highlighted to guide the rational design and practical application of PSCs.

NiCoP modified lead-free double perovskite Cs2AgBiBr6 for efficient photocatalytic hydrogen generation

A NiCoP/Cs2AgBiBr6 composite was successfully synthesised via electrostatic coupling to achieve a hydrogen generation rate of 12.5%, which was ∼88 times higher than that of pure Cs2AgBiBr6.

Methods of Stability Control of Perovskite Solar Cells for High Efficiency

The increasing demand for renewable energy devices over the past decade has motivated researchers to develop new and improve the existing fabrication techniques. One of the promising candidates for renewable energy technology is metal halide perovskite, owning to its high power conversion efficiency and low processing cost. This work analyzes the relationship between the structure of metal halide perovskites and their properties along with the effect of alloying and other factors on device stability, as well as causes and mechanisms of material degradation. The present work discusses the existing approaches for enhancing the stability of PSC devices through modifying functional layers. The advantages and disadvantages of different methods in boosting device efficiency and reducing fabrication cost are highlighted. In addition, the paper presents recommendations for the enhancement of interfaces in PSC structures.

Comparing optical performance of a wide range of perovskite/silicon tandem architectures under real-world conditions

Since single junction c-Si solar cells are reaching their practical efficiency limit. Perovskite/c-Si tandem solar cells hold the promise of achieving greater than 30% efficiencies. In this regard, optical simulations can deliver guidelines for reducing the parasitic absorption losses and increasing the photocurrent density of the tandem solar cells. In this work, an optical study of 2, 3 and 4 terminal perovskite/c-Si tandem solar cells with c-Si solar bottom cells passivated by high thermal-budget poly-Si, poly-SiO_x and poly-SiC_x is performed to evaluate their optical performance with respect to the conventional tandem solar cells employing silicon heterojunction bottom cells. The parasitic absorption in these carrier selective passivating contacts has been quantified. It is shown that they enable greater than 20 mA/cm² matched implied photocurrent density in un-encapsulated 2T tandem architecture along with being compatible with high temperature production processes. For studying the performance of such tandem devices in real-world irradiance conditions and for different locations of the world, the effect of solar spectrum and angle of incidence on their optical performance is studied. Passing from mono-facial to bi-facial tandem solar cells, the photocurrent density in the bottom cell can be increased, requiring again optical optimization. Here, we analyse the effect of albedo, perovskite thickness and band gap as well as geographical location on the optical performance of these bi-facial perovskite/c-Si tandem solar cells. Our optical study shows that bi-facial 2T tandems, that also convert light incident from the rear, require radically thicker perovskite layers to match the additional current from the c-Si bottom cell. For typical perovskite bandgap and albedo values, even doubling the perovskite thickness is not sufficient. In this respect, lower bandgap perovskites are very interesting for application not only in bi-facial 2T tandems but also in related 3T and 4T tandems.