A universal tactic of using Lewis-base polymer-CNTs composites as additives for high performance cm~2-sized and flexible perovskite solar cells

Lewis-base polymers have been widely utilized as additives to act as a template for the perovskite nucleation/crystal growth and passivate the under-coordinated Pb2+ sites.However,it is uncovered in this work that the polymer on the perovskite grain boundaries would significantly hinder the charge transport due to its low conductivity,which brings about free carrier recombination and photocurrent losses.To circumvent this issue while fully exploiting the benefits of polymers in passivating the trap states in perovskite,we incorporate highly conductive multiwall carbon nanotubes(CNTs) with Lewis-base polymers as coadditives in the perovskite film.Functionalizing the CNTs with-COOH group enables a selective hole-extraction and charge transport from perovskite to the hole transporting materials(HTM).By studying the charge transporting and recombination dynamics,we revealed the individual role of the polymer and CNTs in passivating the trap states and facilitating the charge transport,respectively.As a result,the perovskite solar cells(PSCs) with polymer-CNTs composites exhibit an impressive PCE of 21.7% for a small-area device(0.16 cm2) and 20.7% for a large-area device(1.0 cm2).Moreover,due to the superior mechanical flexibility of both polymer and CNTs,the polymer-CNTs composites incorporation in the perovskite film encourages the fabrication of flexible PSCs(f-PSCs) with an impressive PCE of 18.3%,and a strong mechanical durability by retaining 80%of the initial PCE after 1,000 times bending.In addition,we proved that the selection criteria of the polymers can be extended to other long-chain Lewis-base polymers,which opens new possibilities in design and synthesis of inexpensive material for this tactic towards the fabrication of high performance large-area PSCs and f-PSCs.     

High-Efficiency Perovskite Solar Cells Enabled by Anatase TiO2 Nanopyramid Arrays with an Oriented Electric Field

One-dimensional (1D) nanostructured oxides are proposed as excellent electron transport materials (ETMs) for perovskite solar cells (PSCs); however, experimental evidence is lacking. A facile hydrothermal approach was employed to grow highly oriented anatase TiO₂ nanopyramid arrays and demonstrate their application in PSCs. The oriented TiO₂ nanopyramid arrays afford sufficient contact area for electron extraction and increase light transmission. Moreover, the nanopyramid array/perovskite system exhibits an oriented electric field that can increase charge separation and accelerate charge transport, thereby suppressing charge recombination. The anatase TiO₂ nanopyramid array-based PSCs deliver a champion power conversion efficiency of approximately 22.5 %, which is the highest power conversion efficiency reported to date for PSCs consisting of 1D ETMs. This work demonstrates that the rational design of 1D ETMs can achieve PSCs that perform as well as typical mesoscopic and planar PSCs.     

Inorganic p-type semiconductors and carbon materials based hole transport materials for perovskite solar cells

Incorporation of proper inorganic p-type semiconductors as hole transport layer has great potential to increase long-term stability while maintaining high power conversion efficiency of perovskite solar cells with low material cost.     

High‐Efficiency Perovskite Solar Cells Enabled by Anatase TiO2 Nanopyramid Arrays with an Oriented Electric Field

One‐dimensional (1D) nanostructured oxides are proposed as excellent electron transport materials (ETMs) for perovskite solar cells (PSCs); however, experimental evidence is lacking. A facile hydrothermal approach was employed to grow highly oriented anatase TiO₂ nanopyramid arrays and demonstrate their application in PSCs. The oriented TiO₂ nanopyramid arrays afford sufficient contact area for electron extraction and increase light transmission. Moreover, the nanopyramid array/perovskite system exhibits an oriented electric field that can increase charge separation and accelerate charge transport, thereby suppressing charge recombination. The anatase TiO₂ nanopyramid array‐based PSCs deliver a champion power conversion efficiency of approximately 22.5 %, which is the highest power conversion efficiency reported to date for PSCs consisting of 1D ETMs. This work demonstrates that the rational design of 1D ETMs can achieve PSCs that perform as well as typical mesoscopic and planar PSCs.     

Engineering of dendritic dopant-free hole transport molecules:enabling ultrahigh fill factor in perovskite solar cells with optimized dendron construction

Developing dopant-free hole-transporting materials(HTMs)for high-performance perovskite solar cells(PVSCs)has been a very active research topic in recent years since HTMs play a critical role in optimizing interfacial charge carrier kinetics and in turn determining device performance.Here,a novel dendritic engineering strategy is first utilized to design HTMs with a D-A type molecular framework,and diphenylamine and/or carbazole is selected as the building block for constructing dendrons.All HTMs show good thermal stability and excellent film morphology,and the key optoelectronic properties could be fine-tuned by varying the dendron structure.Among them,MPA-Cz-BTI and MCz-Cz-BTI exhibit an improved interfacial contact with the perovskite active layer,and non-radiative recombination loss and charge transport loss can be effectively suppressed.Consequently,high power conversion efficiencies(PCEs)of 20.8%and 21.35%are achieved for MPA-Cz-BTI and MCz-Cz-BTI based devices,respectively,accompanied by excellent long-term storage stability.More encouragingly,ultrahigh fill factors of 85.2%and 83.5%are recorded for both devices,which are among the highest values reported to date.This work demonstrates the great potential of dendritic materials as a new type of dopant-free HTMs for high-performance PVSCs with excellent FF.     

碳量子点纳米材料在铅卤钙钛矿太阳能电池中的应用研究进展

碳量子点（CQDs）是一类粒径较小,光学性能显著,且电荷传输性能优异的类半导体纳米材料,在钙钛矿太阳能电池的性能调控和改善中得到广泛的应用。从CQDs纳米材料的合成、性能及应用出发,综述了CQDs纳米材料在钙钛矿太阳能光电器件中电子传输层、钙钛矿光吸收层和空穴传输层等方面的应用进展,并展望了该类材料调控钙钛矿太阳能器件性能的发展趋势。     

Rapid development in two-dimensional layered perovskite materials and their application in solar cells

This review summarized recent research progresses of two-dimensional layered organic-inorganic hybrid perovskite materials and their photovoltaic performances in 2D perovskite solar cells.     

A mini review: Constructing perovskite p-n homojunction solar cells

Organic metal halide perovskite materials have excellent photoelectric properties, and the power conversion efficiency(PCE) of the perovskite solar cells(PSCs) has increased from 3.8% to more than 25%. In the development of PSCs, innovative architectures were being proposed constantly. However, the use of the electron transport layer(ETL) and hole transport layer(HTL) increases manufacturing costs and process complexity. Perovskite material has ambipolar charge transport characteristics, so it c...     

A review on two-dimensional (2D) and 2D-3D multidimensional perovskite solar cells: Perovskites structures,stability, and photovoltaic performances

Perovskite solar cells (PSCs) fabricated with two-dimensional (2D) halide and 2D-3D mixed-halide materials are remarkable for their optoelectronic properties. The 2D perovskite structures are extremely stable but show limited charge transport and large bandgap for solar cell applications. To overcome these challenges, multidimensional 2D-3D perovskite materials are used to maintain simultaneously, a long-term stability, and high performance. In this review, we discuss the recent progress and the advantages of 2D and 2D-3D perovskite materials as absorber for solar cell applications. First, we discuss the structure and the unique properties of 2D and multidimensional 2D-3D perovskites materials. Second, the stability of 2D and 2D-3D mixed perovskites and the perspects of PSCs are hashed out.     

Cove‐Edge Nanoribbon Materials for Efficient Inverted Halide Perovskite Solar Cells

Two cove‐edge graphene nanoribbons hPDI2‐Pyr‐hPDI2 ( 1 ) and hPDI3‐Pyr‐hPDI3 ( 2 ) are used as efficient electron‐transporting materials (ETMs) in inverted planar perovskite solar cells (PSCs). Devices based on the new graphene nanoribbons exhibit maximum power‐conversion efficiencies (PCEs) of 15.6 % and 16.5 % for 1 and 2 , respectively, while a maximum PCE of 14.9 % is achieved with devices based on [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM). The interfacial effects induced by these new materials are studied using photoluminescence (PL), and we find that 1 and 2 act as efficient electron‐extraction materials. Additionally, compared with PC₆₁BM, these new materials are more hydrophobic and have slightly higher LUMO energy levels, thus providing better device performance and higher device stability.     

钙钛矿太阳能电池电子传输层的制备及应用

目前,有机-无机杂化钙钛矿太阳能电池(PSC)的器件效率已经超过25％.电子传输层作为PSC中的重要组成部分在提取和传输光生电子,阻挡空穴,修饰界面,调节界面能级和减少电荷复合等方面起着关键作用.无机n型材料,例如TiO2、ZnO、SnO2和其他金属氧化物材料具有成本低和稳定性好的特点,经常在传统PSC中被用作电子传输...     

Molecular ferroelectrics for efficient perovskite solar cells

During the past decade,the power conversion efficiencies(PCEs)of organic-inorganic hybrid perovskite solar cells(PSCs)have exceeded 25%[1],which is expected to be one of the candidates for the next generation of thin-film photovoltaic technology.Fundamentally speaking,the performance of PSCs mainly depends on the light absorption capacity,defect passivation and photo-induced exciton separation and extraction of perovskite films.Under the light illumination,photo-induced excitons were separated and extracted by the built-in electric field of PSCs.     

SnO2表面卤化提高钙钛矿太阳能电池光伏性能

钙钛矿太阳能电池(PSCs)成为近几年来迅速发展的新型太阳能电池,其中将SnO₂纳米粒子层用作电子传输层(ETL)的钙钛矿太阳能电池器件得到了广泛的关注。SnO₂有着更低的制备温度,使其具备应用于柔性器件的潜力,但与钙钛矿层能级不匹配等问题限制着其发展。而在界面处加入钝化层,尤其是表面卤化的方法或可解决这一问题。本文综合研究了SnO₂表面卤化对钙钛矿太阳能电池光伏性能的影响,选用四丁基氯化铵(TBAC)、四丁基溴化铵(TBAB)和四丁基碘化铵(TBAI)三种钝化材料对SnO₂表面进行钝化处理,并对钝化材料溶液进行了浓度梯度研究。通过材料形貌、结构和光学性能表征以及电池器件性能测试分析等方法,证明了SnO₂表面卤化可提高钙钛矿层的质量和PSCs光伏性能,并从器件内部电荷传输动力学等角度解释了器件性能改善的原因。为进一步说明其性能改善的机理,采用基于密度泛函理论(DFT)的第一性原理计算方法对材料表面性质进行了深入研究,从能量、结构、电荷密度、态密度、功函数等角度解释了表面卤化提高SnO₂/钙钛矿界面处电子传输特性的原因。实验和理论计算均表明TBAC对于SnO₂具有较好的钝化效果,并随着溶液浓度的提升钝化作用越明显。SnO₂表面卤化作用的深入研究不仅对提高电池器件性能具有实际意义,还能够帮助理解太阳能电池界面现象,为界面改性提供新的研究思路。     

Inverted polymer solar cells with a solution-processed zinc oxide thin film as an electron collection layer

A solution-processed zinc oxide (ZnO) thin film as an electron collection layer for polymer solar cells (PSCs) with an inverted device structure was investigated. Power conversion efficiencies (PCEs) of PSCs made with a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) are 3.50% and 1.21% for PSCs with and without the ZnO thin film, respectively. Light intensity dependence of the photocurrent and the capacitance-voltage measurement demonstrate that the increased PCEs are due to the restriction of the strong bimolecular recombination in the interface when a thin ZnO layer is inserted between the polymer active layer and the ITO electrode. These results demonstrate that the ZnO thin film plays an important role in the performance of PSCs with an inverted device structure.     

Structurally-tuned benzo[1,2-b:4,5:b']dithiophene-based polymer as a dopant-free hole transport material for perovskite solar cells

For highly efficient and stable perovskite solar cells (PSCs), hole transport material (HTM) should be designed and synthesized to afford suitable energy levels, high charge transport, efficient passivation ability, and high device stability. Here, we systematically modulated benzo[1,2-b:4,5:b']dithiophene-based polymer by finely controlling the thienyl and pyridyl contents within the conjugated backbone in order to develop a high performance dopant-free HTM for PSCs. We found that the optimized copolymer with 25% of pyridine content exhibits improved energy level, charge transport, and morphology compared with control homopolymers. As a result, remarkably high power conversion efficiencies up to 21.1% were achieved by employing the optimized polymer as a dopant-free HTM in PSCs.     

Improving open-circuit voltage by a chlorinated polymer donor endows binary organic solar cells efficiencies over 17%

Power conversion efficiency(PCE) of single-junction polymer solar cells(PSCs) has made a remarkable breakthrough recently.Plenty of work was reported to achieve PCEs higher than 16% derived from the PM6:Y6 binary system.To further increase the PCEs of binary OSCs incorporating small molecular acceptor(SMA) Y6,we substituted PM6 with PM7 due to the deeper highest occupied molecular orbital(HOMO) of PM7.Consequently,the PM7:Y6 has achieved PCEs as high as 17.0% by the hotcast method,due to the improved open-circuit voltage(V_(OC)).Compared with PM6,the lower HOMO of PM7 increases the gap between E_(LUMO-donor) and E_(HOMO-acceptor),which is proportional to V_(OC).This research provides a high PCE for single-junction binary PSCs,which is meaningful for device fabrication related to PM7 and commercialization of PSCs.     

Tuning Hole Transport Properties via Pyrrole Derivation for High-Performance Perovskite Solar Cells

Hole transport materials (HTMs) with high hole mobility, good band alignment and ease of fabrication are highly desirable for perovskite solar cells (PSCs). Here, we designed and synthesized novel organic HTMs, named T3, which can be synthesized in high yields with commercially available materials, featuring a substituted pyrrole core and triphenylamine peripheral arms. The capability of functionalization in the final synthetic step provides an efficient way to obtain a variety of T3-based HTMs with tunable energy levels and other properties. Among them, fluorine-substituted T3 (T3-F) exhibits the best band alignment and hole extraction properties, leading to PSCs with outstanding PCEs of 24.85 % and 24.03 % (certified 23.46 %) for aperture areas of 0.1 and 1 cm², respectively. The simple structure and tunable performance of T3 can inspire further optimization for efficient PSCs.     

碳基钙钛矿太阳能电池的研究进展

由于具有成本低、工艺简单等优点,有机-无机杂化太阳能电池(PSCs)的研究和发展受到了广泛的关注,光电转换效率也快速提升到与传统晶体硅太阳能电池相当的水平。 然而,PSCs稳定性差的问题严重限制了其商业化。 在各种PSCs中,基于碳电极的无空穴传输层器件(C-PSCs)去除了影响稳定性的有机空穴传输层和金属电极,使得器件稳定性得到了明显的提高,是最具有应用前景的电池器件之一。 自从2013年首次报道以来,C-PSCs的各方面研究取得了很大的进展,效率也从最初的6.6%提高到现在的15.9%。 本综述将系统地介绍C-PSCs的最新研究进展,包括器件结构和工作原理、各部分研究进展(电子传输层、钙钛矿薄膜和碳电极),以及存在的问题和解决方案。     

Fluorine-Containing Passivation Layer via Surface Chelation for Inorganic Perovskite Solar Cells

Minimizing surface defect is vital to further improve power conversion efficiency (PCE) and stability of inorganic perovskite solar cells (PSCs). Herein, we designed a passivator trifluoroacetamidine (TFA) to suppress CsPbI_3−xBr_x film defects. The amidine group of TFA can strongly chelate onto the perovskite surface to suppress the iodide vacancy, strengthened by additional hydrogen bonds. Moreover, three fluorine atoms allow strong intermolecular connection via intermolecular hydrogen bonds, thus constructing a robust shield against moisture. The TFA-treated PSCs exhibit remarkably suppressed recombination, yielding the record PCEs of 21.35 % and 17.21 % for 0.09 cm² and 1.0 cm² device areas, both of which are the highest for all-inorganic PSCs so far. The device also achieves a PCE of 39.78 % under indoor illumination, the highest for all-inorganic indoor photovoltaic devices. Furthermore, TFA greatly improves device ambient stability by preserving 93 % of the initial PCE after 960 h.     

Material and Interface Engineering for High‐Performance Perovskite Solar Cells: A Personal Journey and Perspective

Hybrid organic‐inorganic perovskite solar cells (PSCs) have become a shining star in the photovoltaic field due to their spectacular increase in power conversion efficiency (PCE) from 3.8 % to over 23 % in just few years, opening up the potential in addressing the important future energy and environment issues. The excellent photovoltaic performance can be attributed to the unique properties of the organometal halide perovskite materials, including high absorption coefficient, tunable bandgap, high defect tolerance, and excellent charge transport characteristics. The authors entered this field when pursuing research on dye‐sensitized solar cells (DSCs) by leveraging nanorods arrays for vectorial transport of the extracted electrons. Soon after, we and others realized that while the organometal halide perovskite materials have excellent intrinsic properties for solar cells, interface engineering is at least equally important in the development of high‐performance PSCs, which includes surface defect passivation, band alignment, and heterojunction formation. Herein, we will address this topic by presenting the historical development and recent progress on the interface engineering of PSCs primarily of our own group. This review is mainly focused on the material and interface design of the conventional n‐i‐p, inverted p‐i‐n and carbon electrode‐based structure devices from our own experience and perspective. Finally, the challenges and prospects of this area for future development will also be discussed.