A Novel Conductive Mesoporous Layer with a Dynamic Two‐Step Deposition Strategy Boosts Efficiency of Perovskite Solar Cells to 20%

Lead halide perovskite solar cells (PSCs) with the high power conversion efficiency (PCE) typically use mesoporous metal oxide nanoparticles as the scaffold and electron‐transport layers. However, the traditional mesoporous layer suffers from low electron conductivity and severe carrier recombination. Here, antimony‐doped tin oxide nanorod arrays are proposed as novel transparent conductive mesoporous layers in PSCs. Such a mesoporous layer improves the electron transport as well as light utilization. To resolve the common problem of uneven growth of perovskite on rough surface, the dynamic two‐step spin coating strategy is proposed to prepare highly smooth, dense, and crystallized perovskite films with micrometer‐scale grains, largely reducing the carrier recombination ratio. The conductive mesoporous layer and high‐quality perovskite film eventually render the PSC with a remarkable PCE of 20.1% with excellent reproducibility. These findings provide a new avenue to further design high‐efficiency PSCs from the aspect of carrier transport and recombination.     

Efficient,Hysteresis‐Free,and Stable Perovskite Solar Cells with ZnO as Electron‐Transport Layer: Effect of Surface Passivation

The power conversion efficiency of perovskite solar cells (PSCs) has ascended from 3.8% to 22.1% in recent years. ZnO has been well‐documented as an excellent electron‐transport material. However, the poor chemical compatibility between ZnO and organo‐metal halide perovskite makes it highly challenging to obtain highly efficient and stable PSCs using ZnO as the electron‐transport layer. It is demonstrated in this work that the surface passivation of ZnO by a thin layer of MgO and protonated ethanolamine (EA) readily makes ZnO as a very promising electron‐transporting material for creating hysteresis‐free, efficient, and stable PSCs. Systematic studies in this work reveal several important roles of the modification: (i) MgO inhibits the interfacial charge recombination, and thus enhances cell performance and stability; (ii) the protonated EA promotes the effective electron transport from perovskite to ZnO, further fully eliminating PSCs hysteresis; (iii) the modification makes ZnO compatible with perovskite, nicely resolving the instability of ZnO/perovskite interface. With all these findings, PSCs with the best efficiency up to 21.1% and no hysteresis are successfully fabricated. PSCs stable in air for more than 300 h are achieved when graphene is used to further encapsulate the cells.     

Extrinsic Ion Distribution Induced Field Effect in CsPbIBr2 Perovskite Solar Cells

Excellent power conversion efficiency (PCE) and stability are the primary forces that propel the all‐inorganic cesium‐based halide perovskite solar cells (PSCs) toward commercialization. However, the intrinsic high density of trap state and internal nonradiative recombination of CsPbIBr₂ perovskite film are the barriers that limit its development. In the present study, a facile additive strategy is introduced to fabricate highly efficient CsPbIBr₂ PSCs by incorporating sulfamic acid sodium salt (SAS) into the perovskite layer. The additive can control the crystallization behaviors and optimize morphology, as well as effectively passivate defects in the bulk perovskite film, thereby resulting in a high‐quality perovskite. In addition, SAS in perovskite has possibly introduced an additional internal electric field effect that favors electron transport and injection due to inhomogeneous ion distribution. A champion PCE of 10.57% (steady‐output efficiency is 9.99%) is achieved under 1 Sun illumination, which surpasses that of the contrast sample by 16.84%. The modified perovskite film also exhibits improved moisture stability. The unencapsulated device maintains over 80% initial PCE after aging for 198 h in air. The results provide a suitable additive for inorganic perovskite and introduce a new conjecture to explain the function of additives in PSCs more rationally.     

Fine Multi‐Phase Alignments in 2D Perovskite Solar Cells with Efficiency over 17% via Slow Post‐Annealing

Layered Ruddlesden–Popper (RP) phase (2D) halide perovskites have attracted tremendous attention due to the wide tunability on their optoelectronic properties and excellent robustness in photovoltaic devices. However, charge extraction/transport and ultimate power conversion efficiency (PCE) in 2D perovskite solar cells (PSCs) are still limited by the non‐eliminable quantum well effect. Here, a slow post‐annealing (SPA) process is proposed for BA₂MA₃Pb₄I₁₃ (n = 4) 2D PSCs by which a champion PCE of 17.26% is achieved with simultaneously enhanced open‐circuit voltage, short‐circuit current, and fill factor. Investigation with optical spectroscopy coupled with structural analyses indicates that enhanced crystal orientation and favorable alignment on the multiple perovskite phases (from the 2D phase near bottom to quasi‐3D phase near top regions) is obtained with SPA treatment, which promotes carrier transport/extraction and suppresses Shockley–Read–Hall charge recombination in the solar cell. As far as it is known, the reported PCE is so far the highest efficiency in RP phase 2D PSCs based on butylamine (BA) spacers (n = 4). The SPA‐processed devices exhibit a satisfactory stability with <4.5% degradation after 2000 h under N₂ environment without encapsulation. The demonstrated process strategy offers a promising route to push forward the performance in 2D PSCs toward realistic photovoltaic applications.     

Amide‐Catalyzed Phase‐Selective Crystallization Reduces Defect Density in Wide‐Bandgap Perovskites

Wide‐bandgap (WBG) formamidinium–cesium (FA‐Cs) lead iodide–bromide mixed perovskites are promising materials for front cells well‐matched with crystalline silicon to form tandem solar cells. They offer avenues to augment the performance of widely deployed commercial solar cells. However, phase instability, high open‐circuit voltage (V_oc) deficit, and large hysteresis limit this otherwise promising technology. Here, by controlling the crystallization of FA‐Cs WBG perovskite with the aid of a formamide cosolvent, light‐induced phase segregation and hysteresis in perovskite solar cells are suppressed. The highly polar solvent additive formamide induces direct formation of the black perovskite phase, bypassing the yellow phases, thereby reducing the density of defects in films. As a result, the optimized WBG perovskite solar cells (PSCs) (E_g ≈ 1.75 eV) exhibit a high V_oc of 1.23 V, reduced hysteresis, and a power conversion efficiency (PCE) of 17.8%. A PCE of 15.2% on 1.1 cm² solar cells, the highest among the reported efficiencies for large‐area PSCs having this bandgap is also demonstrated. These perovskites show excellent phase stability and thermal stability, as well as long‐term air stability. They maintain ≈95% of their initial PCE after 1300 h of storage in dry air without encapsulation.     

Defect‐Engineering‐Enabled High‐Efficiency All‐Inorganic Perovskite Solar Cells

The emergence of cesium lead iodide (CsPbI₃) perovskite solar cells (PSCs) has generated enormous interest in the photovoltaic research community. However, in general they exhibit low power conversion efficiencies (PCEs) because of the existence of defects. A new all‐inorganic perovskite material, CsPbI₃:Br:InI₃, is prepared by defect engineering of CsPbI₃. This new perovskite retains the same bandgap as CsPbI₃, while the intrinsic defect concentration is largely suppressed. Moreover, it can be prepared in an extremely high humidity atmosphere and thus a glovebox is not required. By completely eliminating the labile and expensive components in traditional PSCs, the all‐inorganic PSCs based on CsPbI₃:Br:InI₃ and carbon electrode exhibit PCE and open‐circuit voltage as high as 12.04% and 1.20 V, respectively. More importantly, they demonstrate excellent stability in air for more than two months, while those based on CsPbI₃ can survive only a few days in air. The progress reported represents a major leap for all‐inorganic PSCs and paves the way for their further exploration in order to achieve higher performance.     

Isomer‐Pure Bis‐PCBM‐Assisted Crystal Engineering of Perovskite Solar Cells Showing Excellent Efficiency and Stability

A fullerene derivative (α‐bis‐PCBM) is purified from an as‐produced bis‐phenyl‐C₆₁‐butyric acid methyl ester (bis‐[60]PCBM) isomer mixture by preparative peak‐recycling, high‐performance liquid chromatography, and is employed as a templating agent for solution processing of metal halide perovskite films via an antisolvent method. The resulting α‐bis‐PCBM‐containing perovskite solar cells achieve better stability, efficiency, and reproducibility when compared with analogous cells containing PCBM. α‐bis‐PCBM fills the vacancies and grain boundaries of the perovskite film, enhancing the crystallization of perovskites and addressing the issue of slow electron extraction. In addition, α‐bis‐PCBM resists the ingression of moisture and passivates voids or pinholes generated in the hole‐transporting layer. As a result, a power conversion efficiency (PCE) of 20.8% is obtained, compared with 19.9% by PCBM, and is accompanied by excellent stability under heat and simulated sunlight. The PCE of unsealed devices dropped by less than 10% in ambient air (40% RH) after 44 d at 65 °C, and by 4% after 600 h under continuous full‐sun illumination and maximum power point tracking, respectively.     

In Situ Back‐Contact Passivation Improves Photovoltage and Fill Factor in Perovskite Solar Cells

Organic–inorganic hybrid perovskite solar cells (PSCs) have seen a rapid rise in power conversion efficiencies in recent years; however, they still suffer from interfacial recombination and charge extraction losses at interfaces between the perovskite absorber and the charge–transport layers. Here, in situ back‐contact passivation (BCP) that reduces interfacial and extraction losses between the perovskite absorber and the hole transport layer (HTL) is reported. A thin layer of nondoped semiconducting polymer at the perovskite/HTL interface is introduced and it is shown that the use of the semiconductor polymer permits—in contrast with previously studied insulator‐based passivants—the use of a relatively thick passivating layer. It is shown that a flat‐band alignment between the perovskite and polymer passivation layers achieves a high photovoltage and fill factor: the resultant BCP enables a photovoltage of 1.15 V and a fill factor of 83% in 1.53 eV bandgap PSCs, leading to an efficiency of 21.6% in planar solar cells.     

Quasi‐Heteroface Perovskite Solar Cells

Perovskite solar cells (PSCs) have attracted unprecedented attention due to their rapidly rising photoelectric conversion efficiency (PCE). In order to further improve the PCE of PSCs, new possible optimization path needs to be found. Here, quasi‐heteroface PSCs (QHF‐PSCs) is designed by a double‐layer perovskite film. Such brand new PSCs have good carrier separation capabilities, effectively suppress the nonradiative recombination of the PSCs, and thus greatly improve the open‐circuit voltage and PCE. The root cause of the performance improvement is the benefit from the additional built‐in electric field, which is confirmed by measuring the external quantum efficiency under applied electric field and Kelvin probe force microscope. Meanwhile, an intermediate band gap perovskite layer can be obtained simply by combining a wide band gap perovskite layer with a narrow band gap perovskite layer. Tunability of the band gap is obtained by varying the film thicknesses of the narrow and wide band gap layers. This phenomenon is quite different from traditional inorganic solar cells, whose band gap is determined only by the narrowest band gap layer. It is believed that these QHF‐PSCs will be an effective strategy to further enhance PCE in PSCs and provide basis to further understand and develop the perovskite materials platform.     

Interfacial Passivation of the p‐Doped Hole‐Transporting Layer Using General Insulating Polymers for High‐Performance Inverted Perovskite Solar Cells

Organic–inorganic lead halide perovskite solar cells (PVSCs), as a competing technology with traditional inorganic solar cells, have now realized a high power conversion efficiency (PCE) of 22.1%. In PVSCs, interfacial carrier recombination is one of the dominant energy‐loss mechanisms, which also results in the simultaneous loss of potential efficiency. In this work, for planar inverted PVSCs, the carrier recombination is dominated by the dopant concentration in the p‐doped hole transport layers (HTLs), since the F4‐TCNQ dopant induces more charge traps and electronic transmission channels, thus leading to a decrease in open‐circuit voltages (V_OC). This issue is efficiently overcome by inserting a thin insulating polymer layer (poly(methyl methacrylate) or polystyrene) as a passivation layer with an appropriate thickness, which allows for increases in the V_OC without significantly sacrificing the fill factor. It is believed that the passivation layer attributes to the passivation of interfacial recombination and the suppression of current leakage at the perovskite/HTL interface. By manipulating this interfacial passivation technique, a high PCE of 20.3% is achieved without hysteresis. Consequently, this versatile interfacial passivation methodology is highly useful for further improving the performance of planar inverted PVSCs.     

Simultaneous Bottom‐Up Interfacial and Bulk Defect Passivation in Highly Efficient Planar Perovskite Solar Cells using Nonconjugated Small‐Molecule Electrolytes

Recent perovskite solar cell (PSC) advances have pursued strategies for reducing interfacial energetic mismatches to mitigate energy losses, as well as to minimize interfacial and bulk defects and ion vacancies to maximize charge transfer. Here nonconjugated multi‐zwitterionic small‐molecule electrolytes (NSEs) are introduced, which act not only as charge‐extracting layers for barrier‐free charge collection at planar triple cation PSC cathodes but also passivate charged defects at the perovskite bulk/interface via a spontaneous bottom‐up passivation effect. Implementing these synergistic properties affords NSE‐based planar PSCs that deliver a remarkable power conversion efficiency of 21.18% with a maximum V_OC = 1.19 V, in combination with suppressed hysteresis and enhanced environmental, thermal, and light‐soaking stability. Thus, this work demonstrates that the bottom‐up, simultaneous interfacial and bulk trap passivation using NSE modifiers is a promising strategy to overcome outstanding issues impeding further PSC advances.     

20.67%-Efficiency Inorganic CsPbI3 Solar Cells Enabled by Zwitterion Ion Interface Treatment

All-inorganic CsPbI₃ perovskite solar cells (PSCs) have been extensively studied due to their high thermal stability and unprecedented rise in power conversion efficiency (PCE). Recently, the champion PCE of CsPbI₃ PSCs has reached up to 21%; however, it is still much lower than that of organic–inorganic hybrid PSCs. Interface modification to passivate surface defects and minimize charge recombination and trapping is important to further improve the efficiency of CsPbI₃ PSCs. Herein, a new zwitterion ion is deposited at the interface between electron transporting layer (ETL) and perovskite layer to passivate the defects therein. The zwitterion ions can not only passivate oxygen vacancy (V_O) and iodine vacancy (V_I) defects, but also improve the band alignment at the ETL-perovskite interface. After the interface treatment, the PCE of CsPbI₃ device reaches up to 20.67%, which is among the highest values of CsPbI₃ PSCs so far. Due to the defect passivation and hydrophobicity improvement, the PCE of optimized device remains 94% of its original value after 800 h storing under ambient condition. These results provide an efficient way to improve the quality of ETL-perovskite interface by zwitterion ions for achieving high performance inorganic CsPbI₃ PSCs.     

Interface Engineering for All‐Inorganic CsPbI2Br Perovskite Solar Cells with Efficiency over 14%

In this work, a SnO₂/ZnO bilayered electron transporting layer (ETL) aimed to achieve low energy loss and large open‐circuit voltage (V_oc) for high‐efficiency all‐inorganic CsPbI₂Br perovskite solar cells (PVSCs) is introduced. The high‐quality CsPbI₂Br film with regular crystal grains and full coverage can be realized on the SnO₂/ZnO surface. The higher‐lying conduction band minimum of ZnO facilitates desirable cascade energy level alignment between the perovskite and SnO₂/ZnO bilayered ETL with superior electron extraction capability, resulting in a suppressed interfacial trap‐assisted recombination with lower charge recombination rate and greater charge extraction efficiency. The as‐optimized all‐inorganic PVSC delivers a high V_oc of 1.23 V and power conversion efficiency (PCE) of 14.6%, which is one of the best efficiencies reported for the Cs‐based all‐inorganic PVSCs to date. More importantly, decent thermal stability with only 20% PCE loss is demonstrated for the SnO₂/ZnO‐based CsPbI₂Br PVSCs after being heated at 85 °C for 300 h. These findings provide important interface design insights that will be crucial to further improve the efficiency of all‐inorganic PVSCs in the future.     

Graded Heterojunction Engineering for Hole‐Conductor‐Free Perovskite Solar Cells with High Hole Extraction Efficiency and Conductivity

Despite great progress in the photovoltaic conversion efficiency (PCE) of inorganic–organic hybrid perovskite solar cells (PSCs), the large‐scale application of PSCs still faces serious challenges due to the poor‐stability and high‐cost of the spiro‐OMeTAD hole transport layer (HTL). It is of great fundamental importance to rationally address the issues of hole extraction and transfer arising from HTL‐free PSCs. Herein, a brand‐new PSC architecture is designed by introducing multigraded‐heterojunction (GHJ) inorganic perovskite CsPbBr_x I_3?x layers as an efficient HTL. The grade adjustment can be achieved by precisely tuning the halide proportion and distribution in the CsPbBr_x I_3?x film to reach an optimal energy alignment of the valance and conduction band between MAPbI₃ and CsPbBr_x I_3?x . The CsPbBr_x I_3?x GHJ as an efficient HTL can induce an electric field where a valance/conduction band edge is leveraged to bend at the heterojunction interface, boosting the interfacial electron–hole splitting and photoelectron extraction. The GHJ architecture enhances the hole extraction and conduction efficiency from the MAPbI₃ to the counter electrode, decreases the recombination loss during the hole transfer, and benefits in increasing the open‐circuit voltage. The optimized HTL‐free PCS based on the GHJ architecture demonstrates an outstanding thermal stability and a significantly improved PCE of 11.33%, nearly 40% increase compared with 8.16% for pure HTL‐free devices.     

2D Perovskites with Short Interlayer Distance for High‐Performance Solar Cell Application

2D perovskites have emerged as one of the most promising photovoltaic materials owing to their excellent stability compared with their 3D counterparts. However, in typical 2D perovskites, the highly conductive inorganic layers are isolated by large organic cations leading to quantum confinement and thus inferior electrical conductivity across layers. To address this issue, the large organic cations are replaced with small propane‐1,3‐diammonium (PDA) cations to reduce distance between the inorganic perovskite layers. As shown by optical characterizations, quantum confinement is no longer dominating in the PDA‐based 2D perovskites. This leads to considerable enhancement of charge transport as confirmed with electrochemical impedance spectroscopy, time‐resolved photoluminescence, and mobility measurements. The improved electric properties of the interlayer‐engineered 2D perovskites yield a power conversion efficiency of 13.0%. Furthermore, environmental stabilities of the PDA‐based 2D perovskites are improved. PDA‐based 2D perovskite solar cells (PSCs) with encapsulation can retain over 90% of their efficiency upon storage for over 1000 h, and PSCs without encapsulation can maintain their initial efficiency at 70 °C for over 100 h, which exhibit promising stabilities. These results reveal excellent optoelectronic properties and intrinsic stabilities of the layered perovskites with reduced interlayer distance.     

Efficient and Stable Inverted Perovskite Solar Cells Incorporating Secondary Amines

Large‐bandgap perovskites offer a route to improve the efficiency of energy capture in photovoltaics when employed in the front cell of perovskite–silicon tandems. Implementing perovskites as the front cell requires an inverted (p–i–n) architecture; this architecture is particularly effective at harnessing high‐energy photons and is compatible with ionic‐dopant‐free transport layers. Here, a power conversion efficiency of 21.6% is reported, the highest among inverted perovskite solar cells (PSCs). Only by introducing a secondary amine into the perovskite structure to form MA_1?xDMA_xPbI₃ (MA is methylamine and DMA is dimethylamine) are defect density and carrier recombination suppressed to enable record performance. It is also found that the controlled inclusion of DMA increases the hydrophobicity and stability of films in ambient operating conditions: encapsulated devices maintain over 80% of their efficiency following 800 h of operation at the maximum power point, 30 times longer than reported in the best prior inverted PSCs. The unencapsulated devices show record operational stability in ambient air among PSCs.     

Wearable Large‐Scale Perovskite Solar‐Power Source via Nanocellular Scaffold

Dramatic advances in perovskite solar cells (PSCs) and the blossoming of wearable electronics have triggered tremendous demands for flexible solar‐power sources. However, the fracturing of functional crystalline films and transmittance wastage from flexible substrates are critical challenges to approaching the high‐performance PSCs with flexural endurance. In this work, a nanocellular scaffold is introduced to architect a mechanics buffer layer and optics resonant cavity. The nanocellular scaffold releases mechanical stresses during flexural experiences and significantly improves the crystalline quality of the perovskite films. The nanocellular optics resonant cavity optimizes light harvesting and charge transportation of devices. More importantly, these flexible PSCs, which demonstrate excellent performance and mechanical stability, are practically fabricated in modules as a wearable solar‐power source. A power conversion efficiency of 12.32% for a flexible large‐scale device (polyethylene terephthalate substrate, indium tin oxide‐free, 1.01 cm²) is achieved. This ingenious flexible structure will enable a new approach for development of wearable electronics.     

Atomic‐Layer Deposition‐Assisted Double‐Side Interfacial Engineering for High‐Performance Flexible and Stable CsPbBr3 Perovskite Photodetectors toward Visible Light Communication Applications

Self‐powered photodetectors (PDs) based on inorganic metal halide perovskites are regarded as promising alternatives for the next generation of photodetectors. However, uncontrollable film growth and sluggish charge extraction at interfaces directly limit the sensitivity and response speed of perovskite‐based photodetectors. Herein, by assistance of an atomic layer deposition (ALD) technique, CsPbBr₃ perovskite thin films with preferred orientation and enlarged grain size are obtained on predeposited interfacial modification layers. Thanks to improved film quality and double side interfacial engineering, the optimized CsPbBr₃ (Al₂O₃/CsPbBr₃/TiO₂, ACT) perovskite PDs exhibit outstanding performance with ultralow dark current of 10^?11 A, high detectivity of 1.88 × 10¹³ Jones and broad linear dynamic range (LDR) of 172.7 dB. Significantly, excellent long‐term environmental stability (ambient conditions >100 d) and flexibility stability (>3000 cycles) are also achieved. The remarkable performance is credited to the synergistic effects of high carrier conductivity and collection efficiency, which is assisted by ALD modification layers. Finally, the ACT PDs are successfully integrated into a visible light communication system as a light receiver on transmitting texts, showing a bit rate as high as 100 kbps. These results open the window of high performance all‐inorganic halide perovskite photodetectors and extends to rational applications for optical communication.     

Stable and Efficient Organo‐Metal Halide Hybrid Perovskite Solar Cells via π‐Conjugated Lewis Base Polymer Induced Trap Passivation and Charge Extraction

High‐quality pinhole‐free perovskite film with optimal crystalline morphology is critical for achieving high‐efficiency and high‐stability perovskite solar cells (PSCs). In this study, a p‐type π‐conjugated polymer poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl) thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′] dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl) benzo[1′,2′‐c:4′,5′‐c′] dithiophene‐4,8‐dione))] (PBDB‐T) is introduced into chlorobenzene to form a facile and effective template‐agent during the anti‐solvent process of perovskite film formation. The π‐conjugated polymer PBDB‐T is found to trigger a heterogeneous nucleation over the perovskite precursor film and passivate the trap states of the mixed perovskite film through the formation of Lewis adducts between lead and oxygen atom in PBDB‐T. The p‐type semiconducting and hydrophobic PBDB‐T polymer fills in the perovskite grain boundaries to improve charge transfer for better conductivity and prevent moisture invasion into the perovskite active layers. Consequently, the PSCs with PBDB‐T modified anti‐solvent processing leads to a high‐efficiency close to 20%, and the devices show excellent stability, retaining about 90% of the initial power conversion efficiency after 150 d storage in dry air.     

纳米金属氧化物在钙钛矿电池中的应用研究进展

近几年来, 钙钛矿电池发展迅速, 其单电池效率从最初的3.8%迅速提升至目前20.1%, 接近硅基太阳能电池的光电转换效率。TiO₂、ZnO、Al₂O₃等诸多无机纳米金属氧化物材料作为重要的载流子输运材料与钙钛矿生长骨架也被广泛地应用于钙钛矿电池。依据钙钛矿电池功能结构的差异, 本文分别介绍了此类材料作为钙钛矿电池中的致密层及介孔层的制备方法, 并在此基础上介绍了基于表面修饰、掺杂、复合等氧化物的改性手段调节材料理化性能与氧化物/钙钛矿界面特性, 进而改进钙钛矿电池性能的方法。并阐述了进一步提高钙钛矿电池光电转换效率需要关注的重点问题及展望。