JIALINGBO

Tandem solar cells that pair silicon with a metal halide perovskite are a promising option for surpassing the single-cell efficiency limit. We report a monolithic perovskite/silicon tandem with a certified power conversion efficiency of 29.15%. The perovskite absorber, with a bandgap of 1.68 electron volts, remained phase-stable under illumination through a combination of fast hole extraction and minimized nonradiative recombination at the hole-selective interface. These features were made possible by a self-assembled, methyl-substituted carbazole monolayer as the hole-selective layer in the perovskite cell. The accelerated hole extraction was linked to a low ideality factor of 1.26 and single-junction fill factors of up to 84%, while enabling a tandem open-circuit voltage of as high as 1.92 volts. In air, without encapsulation, a tandem retained 95% of its initial efficiency after 300 hours of operation.

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Jiabao Yang, Qi Cao, Ziwei He, Xingyu Pu, Tongtong Li, Bingyu Gao, Xuanhua Li

Publication date: 17 February 2021

Source: Joule, Volume 5, Issue 2

Author(s): Shaobing Xiong, Zhangyu Hou, Shijie Zou, Xiaoshuang Lu, Jianming Yang, Tianyu Hao, Zihao Zhou, Jianhua Xu, Yihan Zeng, Wei Xiao, Wei Dong, Danqin Li, Xiang Wang, Zhigao Hu, Lin Sun, Yuning Wu, Xianjie Liu, Liming Ding, Zhenrong Sun, Mats Fahlman

A facile yet effective thioamides passivation strategy is proposed to suppress defects at the surface and grain boundary of CsSnI₃ perovskite, which reduces the deep level trap density from undercoordinated Sn²⁺ and Sn²⁺ oxidation. The surface passivated CsSnI₃ perovskite solar cell (PSC) delivers a efficiency of 8.20% which is the highest among all lead‐free all‐inorganic PSCs.

Abstract

Despite remarkable progress in hybrid perovskite solar cells (PSCs), the concern of toxic lead ions remains a major hurdle in the path towards PSC's commercialization; tin (Sn)‐based PSCs outperform the reported Pb‐free perovskites in terms of photovoltaic performance. However, it is of a particularly great challenge to develop effective passivation strategies to suppress Sn(II) induced defect densities and oxidation for attaining high‐performance all‐inorganic CsSnI₃ PSCs. Herein, a facile yet effective thioamides passivation strategy to modulate defect state density at surfaces and grain boundaries in CsSnI₃ perovskites is reported. The thiosemicarbazide (TSC) with SCN functional groups can make strong coordination interaction with charge defects, leading to enhanced electron cloud density around defects and increased vacancy formation energies. Importantly, the surface passivation can reduce the deep level trap state defect density originated from undercoordinated Sn²⁺ ion and Sn²⁺ oxidation, significantly restraining nonradiative recombination and elongating the carrier lifetime of TSC treated CsSnI₃ PSCs. The surface passivated all‐inorganic CsSnI₃ PSCs based on an inverted configuration delivers a champion power conversion efficiency (PCE) of 8.20%, with a prolonged lifetime over 90% of initial PCE, after 500 h of continuous illumination. The present strategy sheds light on surface defect passivation for achieving highly efficient all‐inorganic lead‐free Sn‐based PSCs.

Publication date: April 2021

Source: Nano Today, Volume 37

Author(s): Huilin Li, Fumin Li, Zhitao Shen, Su-Ting Han, Junwei Chen, Chao Dong, Chong Chen, Ye Zhou, Mingtai Wang

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Sisi Wang, Zhipeng Zhang, Zikang Tang, Chenliang Su, Wei Huang, Ying Li, Guichuan Xing

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Junsheng Luo, Fangyan Lin, Jianxing Xia, Hua Yang, Ruilin Zhang, Haseeb Ashraf Malik, Hongyu Shu, Zhongquan Wan, Keli Han, Ruilin Wang, Xiaojun Yao, Chunyang Jia

Nonfullerene acceptors dominate organic solar cell research due to their promising high device efficiencies. However, key challenges for achieving high stability in commercially viable devices still remain. In this review, recent progress and challenges toward stable organic solar cells are discussed correlating molecular design and device engineering to device stability.

Abstract

Organic solar cells (OSCs) based on nonfullerene acceptors (NFAs) have made significant breakthrough in their device performance, now achieving a power conversion efficiency of ≈18% for single junction devices, driven by the rapid development in their molecular design and device engineering in recent years. However, achieving long‐term stability remains a major challenge to overcome for their commercialization, due in large part to the current lack of understanding of their degradation mechanisms as well as the design rules for enhancing their stability. In this review, the recent progress in understanding the degradation mechanisms and enhancing the stability of high performance NFA‐based OSCs is a specific focus. First, an overview of the recent advances in the molecular design and device engineering of several classes of high performance NFA‐based OSCs for various targeted applications is provided, before presenting a critical review of the different degradation mechanisms identified through photochemical‐, photo‐, and morphological degradation pathways. Potential strategies to address these degradation mechanisms for further stability enhancement, from molecular design, interfacial engineering, and morphology control perspectives, are also discussed. Finally, an outlook is given highlighting the remaining key challenges toward achieving the long‐term stability of NFA‐OSCs.

Self‐assembled P3HT‐COOH is an excellent hole extraction layer to fabricate robust, high‐performance, and extremely reproducible perovskite solar cells. The well‐aligned self‐assembled P3HT‐COOH generates a dipole layer between indium tin oxide and perovskite, substantially retarding interface charge recombination and producing highly sensitive devices to dim light. The enhanced crystallinity and preferred out‐of‐plane orientation play a key role to suppress the device degradation process.

Abstract

Crystallinity and crystal orientation have a predominant impact on a materials’ semiconducting properties, thus it is essential to manipulate the microstructure arrangements for desired semiconducting device performance. Here, ultra‐uniform hole‐transporting material (HTM) by self‐assembling COOH‐functionalized P3HT (P3HT‐COOH) is fabricated, on which near single crystal quality perovskite thin film can be grown. In particular, the self‐assembly approach facilitates the P3HT‐COOH molecules to form an ordered and homogeneous monolayer on top of the indium tin oxide (ITO) electrode facilitate the perovskite crystalline film growth with high quality and preferred orientations. After detailed spectroscopy and device characterizations, it is found that the carboxylic acid anchoring groups can down‐shift the work function and passivate the ITO surface, retarding the interface carrier recombination. As a result, the device made with the self‐assembled HTM show high open‐circuit voltage over 1.10 V and extend the lifetime over 4,300 h when storing at 30% relative humidity. Moreover, the cell works efficiently under much reduced light power, making it useful as power source under dim‐light conditions. The demonstration suggests a new facile way of fabricating monolayer HTM for high efficiency perovskite devices, as well as the interconnecting layer needed for tandem cell.

Publication date: April 2021

Source: Nano Energy, Volume 82

Author(s): Eunmi Cho, Young Yun Kim, Dong Seok Ham, Jae Heung Lee, Jin-Seong Park, Jangwon Seo, Sang-Jin Lee

Nature Energy, Published online: 04 January 2021; doi:10.1038/s41560-020-00749-7

The mystery of the buried interface in perovskite photovoltaics is deciphered by combining advanced spectroscopy techniques with a lift‐off strategy. The findings open a new avenue to understanding performance losses and thus the design of unique passivation strategies to remove imperfections at the top surfaces and buried interfaces of perovskite photovoltaics, resulting in substantial enhancement in device performance.

Abstract

Understanding the fundamental properties of buried interfaces in perovskite photovoltaics is of paramount importance to the enhancement of device efficiency and stability. Nevertheless, accessing buried interfaces poses a sizeable challenge because of their non‐exposed feature. Herein, the mystery of the buried interface in full device stacks is deciphered by combining advanced in situ spectroscopy techniques with a facile lift‐off strategy. By establishing the microstructure–property relations, the basic losses at the contact interfaces are systematically presented, and it is found that the buried interface losses induced by both the sub‐microscale extended imperfections and lead‐halide inhomogeneities are major roadblocks toward improvement of device performance. The losses can be considerably mitigated by the use of a passivation‐molecule‐assisted microstructural reconstruction, which unlocks the full potential for improving device performance. The findings open a new avenue to understanding performance losses and thus the design of new passivation strategies to remove imperfections at the top surfaces and buried interfaces of perovskite photovoltaics, resulting in substantial enhancement in device performance.

Currently, the further performance improvement for inverted perovskite solar cells (PVSCs) is mainly limited by the high open circuit voltage ( V OC ) loss caused by the detrimental non‐radiative recombination (NRR) processes. Herein, we report a simple and efficient way to simultaneously reduce the NRR processes inside perovskite and at the interface by rationally designing a new pyridine‐based polymer hole transporting material (HTM), i. e. PPY2 , which exhibits suitable energy levels with perovskites, high hole mobility, effective passivation of the uncoordinated Pb 2+ and iodide defects, as well as the capability of promoting the formation of high quality polycrystalline perovskite film. In absence of any dopants, the inverted PVSCs using PPY2 as the HTM deliver an encouraging PCE up to 22.41% with a small V OC loss (0.40 eV), among the best device performance for inverted PVSCs reported so far. Furthermore, PPY2 ‐based unencapsulated devices show an excellent long‐term photostability, and over 97% of its initial PCE can be maintained after one sun constant illumination for 500 h.

The time‐resolved grazing‐incidence wide‐angle X‐ray scattering technique provides real‐time insights on the phase‐transition during the organic cation coating and perovskite quantum wells (PQWs)/3D architecture formation mechanism. With fluorinated poly(triarylamine) (PTAA) as a dopant‐free hole‐transport layer, this PQWs/3D architecture leads to stable perovskite photovoltaics with power conversion efficiency of >22%.

Abstract

The combination of a bulk 3D perovskite layer and a reduced dimensional perovskite layer (perovskite quantum wells (PQWs)) is demonstrated to enhance the performance of perovskite solar cells (PSCs) significantly in terms of stability and efficiency. This perovskite hierarchy has attracted intensive research interest; however, the in‐depth formation mechanism of perovskite quantum wells on top of a 3D perovskite layer is not clearly understood and is therefore the focus of this study. Along with ex situ morphology and photophysical characterization, the time‐resolved grazing‐incidence wide‐angle X‐ray scattering (TS‐GIWAXS) technique performed in this study provides real‐time insights on the phase‐transition during the organic cation (HTAB ligand molecule) coating and PQWs/3D architecture formation process. A strikingly strong ionic reaction between the 3D perovskite and the long‐chain organic cation leads to the quick formation of an ordered intermediate phase within only a few seconds. The optimal PQWs/3D architecture is achieved by controlling the HTAB casting, which is assisted by time‐of‐flight SIMS characterization. By controlling the second ionic reaction during the long‐chain cation coating process, along with the fluorinated poly(triarylamine) (PTAA) as a hole‐transport layer, the perovskite solar cells demonstrate efficiencies exceeding 22% along with drastically improved device stability.

Two sequentially deposited SnO₂ layers doped with a low and a high amount of ammonium chloride, respectively, boost the open‐circuit voltage and fill factor of perovskite solar cells. The main effect of the novel electron transport layer is a change in the energy level alignment with the perovskite interface leading to decreased carrier recombination.

Abstract

Tin oxide (SnO₂) is an emerging electron transport layer (ETL) material in halide perovskite solar cells (PSCs). Among current limitations, open‐circuit voltage (V _OC) loss is one of the major factors to be addressed for further improvement. Here a bilayer ETL consisting of two SnO₂ nanoparticle layers doped with different amounts of ammonium chloride is proposed. As demonstrated by photoelectron spectroscopy and photophysical studies, the main effect of the novel ETL is to modify the energy level alignment at the SnO₂/perovskite interface, which leads to decreased carrier recombination, enhanced electron transfer, and reduced voltage loss. Moreover, X‐ray diffraction reveals reduced strain in perovskite layers grown on bilayer ETLs with respect to single‐layer ETLs, further contributing to a decrease of carrier recombination processes. Finally, the bilayer approach enables the more reproducible preparation of smooth and pinhole‐free ETLs as compared to single‐step deposition ETLs. PSCs with the doped bilayer SnO₂ ETL demonstrate strongly increased V _OC values of up to 1.21 V with a power conversion efficiency of 21.75% while showing negligible hysteresis and enhanced stability. Moreover, the SnO₂ bilayer can be processed at low temperature (70 °C), and has therefore a high potential for use in tandem devices or flexible PSCs.

Highly efficient CsPbI_1.5Br_1.5 perovskite solar cells (PSCs) are achieved via introducing fluorescein isothiocyanate (FITC) organic dye as passivator. FITC not only reduces the metal ion related trap states but also improves film crystallinity, resulting in an enhancement of device efficiency from 12.3% to 14.05%. In addition, it is demonstrated that CsPbI_1.5Br_1.5 perovskite shows the optimal halide composition for inorganic PSCs.

Abstract

All‐inorganic perovskite solar cells (PSCs) have recently received growing attention as a promising template to solve the thermal instability of organic–inorganic PSCs. However, the thermodynamic phase instability and relatively low device efficiency pose challenges. Herein, highly efficient and stable CsPbI_1.5Br_1.5 compositional perovskite‐based inorganic PSCs are fabricated using an organic dye, fluorescein isothiocyanate (FITC), as a passivator. The carboxyl and thiocyanate groups of FITC not only minimize the trap states by forming interactions with the under‐coordinated Pb²⁺ ions but also significantly increase the grain size and improve the crystallinity of the perovskite films during annealing. Consequently, perovskite films with superior optoelectronic properties, prolonged carrier lifetime, reduced trap density, and improved stability are obtained. The resulting device yields a champion efficiency of 14.05% with negligible hysteresis, which presents the highest reported efficiency for inorganic CsPbI_1.5Br_1.5 solar cells reported thus far. In addition, FITC can be generally adopted as attractive passivator to improve the performance of CsPbI₂Br‐ and CsPbIBr₂‐based PSCs. Furthermore, with a comprehensive comparison of mixed‐halide inorganic perovskites, it is demonstrated that CsPbI_1.5Br_1.5 compositional perovskite is a promising candidate with the optimal halide composition for high‐performance inorganic PSCs.

Publication date: March 2021

Source: Nano Energy, Volume 81

Author(s): Furkan H. Isikgor, Anand S. Subbiah, Mathan K. Eswaran, Calvyn T. Howells, Aslihan Babayigit, Michele De Bastiani, Emre Yengel, Jiang Liu, Francesco Furlan, George T. Harrison, Shynggys Zhumagali, Jafar I. Khan, Frédéric Laquai, Thomas D. Anthopoulos, Iain McCulloch, Udo Schwingenschlögl, Stefaan De Wolf