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.     

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.     

Record Efficiency Stable Flexible Perovskite Solar Cell Using Effective Additive Assistant Strategy

Even though the power conversion efficiency (PCE) of rigid perovskite solar cells is increased to 22.7%, the PCE of flexible perovskite solar cells (F‐PSCs) is still lower. Here, a novel dimethyl sulfide (DS) additive is developed to effectively improve the performance of the F‐PSCs. Fourier transform infrared spectroscopy reveals that the DS additive reacts with Pb²⁺ to form a chelated intermediate, which significantly slows down the crystallization rate, leading to large grain size and good crystallinity for the resultant perovskite film. In fact, the trap density of the perovskite film prepared using the DS additive is reduced by an order of magnitude compared to the one without it, demonstrating that the additive effectively retards transformation kinetics during the thin film formation process. As a result, the PCE of the flexible devices increases to 18.40%, with good mechanical tolerance, the highest reported so far for the F‐PSCs. Meanwhile, the environmental stability of the F‐PSCs significantly enhances by 1.72 times compared to the device without the additive, likely due to the large grain size that suppresses perovskite degradation at grain boundaries. The present strategy will help guide development of high efficiency F‐PSCs for practical applications.     

具有2D-EDAPbI4薄覆盖层的环境稳定的FAPbI3基钙钛矿太阳能电池（英文）

二维(2D)卤化铅钙钛矿材料是钙钛矿太阳能电池(PSC)中最有前途的吸光材料之一,具有优异的稳定性和缺陷钝化作用.然而,这些稳定的二维PSC的转换效率仍远远落后于三维钙钛矿电池.在本文中我们通过原位生长的方法将2D EDAPbI4层成功制备在3D FAPbI3层表面。这种合理设计的2D-3D钙钛矿薄膜分层结构可以明显提高电池的效率.另外,由于EDAPbI4层的高抗湿性和抑制迁移, 2D-3D电池器件显示出明显增强的长期稳定性,在200 h内一直保持初始转换效率,甚至在500 h后仍能保持其初始转化效率的90%.     

Dual function of a high-contrast hydrophobic-hydrophilic coating for enhanced stability of perovskite solar cells in extremely humid environments

In spite of a continuous increase in their power conversion efficiency (PCE) and an economically viable fabrication process,organic-inorganic perovskite solar cells (PSCs) pose a significant problem when used in practical applications:They show fast degradation of the PCE when exposed to very humid environments.In this study,the stability of PSCs under very humid conditions is greatly enhanced by coating the surface of the PSC devices with a multi-layer film consisting of ultrahydrophobic and relatively hydrophilic layers.A hydrophobic composite of poly(methyl methacrylate) (PMMA),polyurethane (PU),and SiO2 nanoparticles successfully retards the water molecules from very humid surroundings.Also,the hydrophilic layer with moderately PMMA captures the residual moisture within the perovskite layer;subsequently,the perovskite layer recovers.This dual function of the coating film keeps the PCE of PSCs at 17.3％ for 180 min when exposed to over 95％ humidity.     

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.     

Methodologies toward Highly Efficient Perovskite Solar Cells

A perovskite solar cell (PSC) employing an organic–inorganic lead halide perovskite light harvester, seeded in 2009 with power conversion efficiency (PCE) of 3.8% and grown in 2011 with PCE of 6.5% in dye‐sensitized solar cell structure, has received great attention since the breakthrough reports ≈10% efficient solid‐state PCSs demonstrating 500 h stability. Developments of device layout and high‐quality perovskite film eventually lead to a PCE over 22%. As of October 31, 2017, the highest PCE of 22.7% is listed in an efficiency chart provided by NREL. In this Review, the methodologies to obtain highly efficient PSCs are described in detail. In order to achieve a PCE of over 20% reproducibly, key technologies are disclosed from the viewpoint of precursor solution chemistry, processing for defect‐free perovskite films, and passivation of grain boundaries. Understanding chemical species in precursor solution, crystal growth kinetics, light–matter interaction, and controlling defects is expected to give important insights into not only reproducible production of high PCE over 20% but also further enhancement of the PCE of PCSs.     

Extending the Photovoltaic Response of Perovskite Solar Cells into the Near‐Infrared with a Narrow‐Bandgap Organic Semiconductor

Typical lead‐based perovskites solar cells show an onset of photogeneration around 800 nm, leaving plenty of spectral loss in the near‐infrared (NIR). Extending light absorption beyond 800 nm into the NIR should increase photocurrent generation and further improve photovoltaic efficiency of perovskite solar cells (PSCs). Here, a simple and facile approach is reported to incorporate a NIR‐chromophore that is also a Lewis‐base into perovskite absorbers to broaden their photoresponse and increase their photovoltaic efficiency. Compared with pristine PSCs without such an organic chromophore, these solar cells generate photocurrent in the NIR beyond the band edge of the perovskite active layer alone. Given the Lewis‐basic nature of the organic semiconductor, its addition to the photoactive layer also effectively passivates perovskite defects. These films thus exhibit significantly reduced trap densities, enhanced hole and electron mobilities, and suppressed illumination‐induced ion migration. As a consequence, perovskite solar cells with organic chromophore exhibit an enhanced efficiency of 21.6%, and substantively improved operational stability under continuous one‐sun illumination. The results demonstrate the potential generalizability of directly incorporating a multifunctional organic semiconductor that both extends light absorption and passivates surface traps in perovskite active layers to yield highly efficient and stable NIR‐harvesting PSCs.     

Perovskite Solar Cells with Inorganic Electron‐ and Hole‐Transport Layers Exhibiting Long‐Term (≈500 h) Stability at 85 °C under Continuous 1 Sun Illumination in Ambient Air

Despite the high power conversion efficiency (PCE) of perovskite solar cells (PSCs), poor long‐term stability is one of the main obstacles preventing their commercialization. Several approaches to enhance the stability of PSCs have been proposed. However, an accelerating stability test of PSCs at high temperature under the operating conditions in ambient air remains still to be demonstrated. Herein, interface‐engineered stable PSCs with inorganic charge‐transport layers are shown. The highly conductive Al‐doped ZnO films act as efficient electron‐transporting layers as well as dense passivation layers. This layer prevents underneath perovskite from moisture contact, evaporation of components, and reaction with a metal electrode. Finally, inverted‐type PSCs with inorganic charge‐transport layers exhibit a PCE of 18.45% and retain 86.7% of the initial efficiency for 500 h under continuous 1 Sun illumination at 85 °C in ambient air with electrical biases (at maximum power point tracking).     

基于对氯苄胺的2D/3D钙钛矿太阳能电池

三维(3D)有机–无机金属卤化物钙钛矿薄膜的表面和晶界处存在大量缺陷,容易导致载流子的非辐射复合并加快3D钙钛矿分解,进而影响钙钛矿太阳能电池(PSCs)能量转换效率(PCE)及稳定性.本研究通过引入对氯苄胺阳离子,与3D钙钛矿薄膜及其表面过剩的碘化铅反应后原位形成了二维(2D)钙钛矿,实现了对3D钙钛矿薄膜表面和晶界...     

倒置钙钛矿太阳能电池的空穴传输层的研究进展

倒置钙钛矿太阳能电池(PSCs)具有器件结构简单、吸光系数高、迟滞效应小、良好的缺陷容忍性等优点,受到了广泛的关注。但倒置器件光电转换效率(PCE)尚有待提高,究其原因是空穴传输层(HTL)和钙钛矿层界面处的能量损失表现出相对较小的开路电压。文章综述了包括有机聚合物、无机物、尖晶石氧化物等作为空穴传输材料的相关研究进展,进一步分析了通过调节电极/空穴传输层能级使之与钙钛矿价带匹配,及通过界面修饰促进器件对载流子的注入与收集,从而提高光电转换效率的研究现状。对提高倒置钙钛矿太阳能电池性能的研究具有一定的指导意义,最后对倒置器件的应用前景进行了展望。     

Stable and High-Efficiency Methylammonium-Free Perovskite Solar Cells

Organic–inorganic metal halide perovskite solar cells (PSCs) have achieved certified power conversion efficiency (PCE) of 25.2% with complex compositional and bandgap engineering. However, the thermal instability of methylammonium (MA) cation can cause the degradation of the perovskite film, remaining a risk for the long-term stability of the devices. Herein, a unique method is demonstrated to fabricate highly phase-stable perovskite film without MA by introducing cesium chloride (CsCl) in the double cation (Cs, formamidinium) perovskite precursor. Moreover, due to the suboptimal bandgap of bromide (Br⁻), the amount of Br⁻ is regulated, leading to high power conversion efficiency. As a result, MA-free perovskite solar cells achieve remarkable long-term stability and a PCE of 20.50%, which is one of the best results for MA-free PSCs. Moreover, the unencapsulated device retains about 80% of the original efficiencies after a 1000 h aging study. These results provide a feasible approach to enhance solar cell stability and performance simultaneously, paving the way for commercializing PSCs.     

Co-Solvent Engineering Contributing to Achieve High-Performance Perovskite Solar Cells and Modules Based on Anti-Solvent Free Technology

The pinhole-free and defect-less perovskite film is crucial for achieving high efficiency and stable perovskite solar cells (PSCs), which can be prepared by widely used anti-solvent crystallization strategies. However, the involvement of anti-solvent requires precise control and inevitably brings toxicity in fabrication procedures, which limits its large-scale industrial application. In this work, a facile and effective co-solvent engineering strategy is introduced to obtain high- quality perovskite film while avoiding the usage of anti-solvent. The uniform and compact perovskite polycrystalline films have been fabricated through the addition of co-solvent that owns strong coordination capacity with perovskite components , meanwhile possessing the weaker interaction with main solvent . With those strategies, a champion power conversion efficiency (PCE) of 22% has been achieved with the optimal co-solvent, N-methylpyrrolidone (NMP) and without usage of anti-solvent. Subsequently, PSCs based on NMP show high repeatability and good shelf stability (80% PCE remains after storing in ambient condition for 30 days). Finally, the perovskite solar module (5 × 5 cm) with 7 subcells connects in series yielding champion PCE of 16.54%. This strategy provides a general guidance of co-solvent selection for PSCs based on anti-solvent free technology and promotes commercial application of PSCs.     

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.     

基于能带工程制备氧化镍基底的高效锡-铅共混钙钛矿太阳能电池

钙钛矿叠层太阳能电池因为具有超过肖克利-奎伊瑟效率极限的潜力而备受关注.窄带隙锡-铅(Sn-Pb)共混钙钛矿太阳能电池(PSCs)在钙钛矿叠层太阳能电池的构建中起着关键作用.制备稳定性好、可低温处理的空穴输送层是构建高效Sn-Pb钙钛矿太阳能电池和钙钛矿叠层太阳能电池的关键.在此,我们开发了一种室温处理的纳米晶体氧化镍...     

Conjugated Polymer Photovoltaic Materials with Broad Absorption Band and High Charge Carrier Mobility

Polymer solar cells (PSCs) have attracted great attention in recent years because of their advantages of easy fabrication, low cost, light weight, and potential for flexible devices. However, the power conversion efficiency (PCE) of the PSCs needs to be improved for future commercial applications. Factors limiting the PCE of the PSCs include the low exploitation of sunlight due to the narrow absorption band of conjugated polymers, and the low charge‐transport efficiency in the devices due to the lower charge‐carrier mobility of the polymer photovoltaic materials. In this Research News article, recent progress in new conjugated polymer photovoltaic materials fabricated by our group and others is reviewed, including polythiophene (PT) and poly(thienylene vinylene) derivatives with conjugated side chains for a broad absorption band, crosslinked PT derivatives with conjugated bridges for higher hole mobility, and low‐bandgap donor–acceptor copolymers for broad, red‐shifted absorption to match the solar spectrum.     

Efficient and Stable CsPbI3 Solar Cells via Regulating Lattice Distortion with Surface Organic Terminal Groups

All‐inorganic cesium lead iodide perovskites (CsPbI₃) are promising wide‐bandgap materials for use in the perovskite/silicon tandem solar cells, but they easily undergo a phase transition from a cubic black phase to an orthorhombic yellow phase under ambient conditions. It is shown that this phase transition is triggered by moisture that causes distortion of the corner‐sharing octahedral framework ([PbI₆]^4?). Here, a novel strategy to suppress the octahedral tilting of [PbI₆]^4? units in cubic CsPbI₃ by systematically controlling the steric hindrance of surface organic terminal groups is provided. This steric hindrance effectively prevents the lattice distortion and thus increases the energy barrier for phase transition. This mechanism is verified by X‐ray diffraction measurements and density functional theory calculations. Meanwhile, the formation of an organic capping layer can also passivate the surface electronic trap states of perovskite absorber. These modifications contribute to a stable power conversion efficiency (PCE) of 13.2% for the inverted planar perovskite solar cells (PSCs), which is the highest efficiency achieved by the inverted‐structure inorganic PSCs. More importantly, the optimized devices retained 85% of their initial PCE after aging under ambient conditions for 30 days.     

Reducing Hysteresis and Enhancing Performance of Perovskite Solar Cells Using Low‐Temperature Processed Y‐Doped SnO2 Nanosheets as Electron Selective Layers

Despite the rapid increase of efficiency, perovskite solar cells (PSCs) still face some challenges, one of which is the current–voltage hysteresis. Herein, it is reported that yttrium‐doped tin dioxide (Y‐SnO₂) electron selective layer (ESL) synthesized by an in situ hydrothermal growth process at 95 °C can significantly reduce the hysteresis and improve the performance of PSCs. Comparison studies reveal two main effects of Y doping of SnO₂ ESLs: (1) it promotes the formation of well‐aligned and more homogeneous distribution of SnO₂ nanosheet arrays (NSAs), which allows better perovskite infiltration, better contacts of perovskite with SnO₂ nanosheets, and improves electron transfer from perovskite to ESL; (2) it enlarges the band gap and upshifts the band energy levels, resulting in better energy level alignment with perovskite and reduced charge recombination at NSA/perovskite interfaces. As a result, PSCs using Y‐SnO₂ NSA ESLs exhibit much less hysteresis and better performance compared with the cells using pristine SnO₂ NSA ESLs. The champion cell using Y‐SnO₂ NSA ESL achieves a photovoltaic conversion efficiency of 17.29% (16.97%) when measured under reverse (forward) voltage scanning and a steady‐state efficiency of 16.25%. The results suggest that low‐temperature hydrothermal‐synthesized Y‐SnO₂ NSA is a promising ESL for fabricating efficient and hysteresis‐less PSC.     

Tailoring interface of lead-halide perovskite solar cells

Lead-halide perovskite solar cells (PSCs) have attracted tremendous attention during the past few years owing to their extraordinary electronic and photonic properties.To improve the performances of PSCs,many researchers have focused on the compositional engineering,solvent engineering,and film fabrication methodologies.Interfacial engineering of PSCs has become a burgeoning field in which researchers aim to deeply understand the mechanisms of cells and thereby increase the efficiency and stability of PSCs.This review focuses on the interface tailoring of lead-halide PSCs,including the modification of each layer of the cell structure (i.e.,perovskite absorber,electron-transport layers,and holetransport layers) and the interfacial materials that can be introduced into the PSCs.     

基于印刷技术制备钙钛矿太阳电池

近年来,钙钛矿太阳电池(Perovskite solar cells,PSCs)以其优异的光电转换性能和溶液制备成本低等优势受到了科研工作者和产业界人士的广泛关注,被认为是新一代薄膜太阳电池技术中的杰出代表.目前,钙钛矿太阳电池的光电转换效率(Power conversion efficiency,PCE)已经从2009年报道的3.8%迅速提升到现在的22.7%,达到商业化多晶硅、碲化镉、铜铟镓硒等太阳电池水平.目前,溶液旋涂法是实验室制备钙钛矿太阳电池的常用方法.虽然旋涂法操作简单、成膜速度快、重复性好,然而该法缺点也很明显:(1)材料浪费严重;(2)不具备图案化功能;(3)不适用于工业化的连续生产.因此,溶液旋涂技术无法满足钙钛矿太阳电池今后大规模工业化生产所需的大面积、低成本等制造要求.从实验室小面积器件制备转变到可大面积的产业化制备以及降低钙钛矿太阳电池的生产成本,将是钙钛矿太阳电池产业化过程中的一个重要课题.在钙钛矿太阳电池的制备方法中,印刷技术因具有材料利用率高、成本低、工艺效率高、可大面积制备、适用于柔性基底等特点而备受关注.基于印刷工艺制备的小面积钙钛矿太阳电池效率已接近20%,大面积(>10 cm2)钙钛矿太阳电池效率在10%~16%之间,大面积柔性钙钛矿太阳电池效率为10%左右.然而,从实验室小器件转变到大规模工业化生产依旧存在许多问题亟待解决.例如:(1)为了加快钙钛矿材料的结晶,在钙钛矿薄膜退火过程中通常采用溶剂工程或惰性气体辅助的方式,这将导致印刷的大面积钙钛矿薄膜质量难以控制以及重复性降低;(2)退火过程中较高的退火温度会限制柔性基底和界面材料的选择;(3)钙钛矿材料本身对空气湿度敏感,需提高钙钛矿层制备过程的环境适应性,降低制备工艺本身对环境条件的限制等.基于此,完善钙钛矿太阳电池的印刷制备工艺并使其适用于工业化生产显得十分重要.本文综述了基于喷墨打印(Inkj et-printing)、喷涂(Spray-coating)、狭缝涂布(Slot-die coating)、刮涂(Doctor-blading)等印刷技术制备钙钛矿太阳电池的研究进展,并对印刷技术制备钙钛矿太阳电池的前景进行了展望.