Chen Weijie

Publication date: 21 November 2018

Source: Joule, Volume 2, Issue 11

Author(s): Jianyu Yuan, Xufeng Ling, Di Yang, Fangchao Li, Sijie Zhou, Junwei Shi, Yuli Qian, Jiaxin Hu, Yuansheng Sun, Yingguo Yang, Xingyu Gao, Steffen Duhm, Qiao Zhang, Wanli Ma

Context & Scale

Summary

Graphical Abstract

Two‐dimensional perovskites typically have a general formula of (RNH₃)₂MA _{n −1}M _n X_{3 n +1}, and can be arbitrarily categorized into strict 2D (n = 1), quasi‐2D (n = 2−5), and quasi‐3D (n > 5). Research progress in each category is summarized, and it is proposed that designing functional organics to manipulate the optoelectronic properties of 2D perovskites can lead to unique device applications.

Abstract

2D perovskites are recently attracting a significant amount of attention, mainly due to their improved stability compared with their 3D counterpart, e.g., the archetypical MAPbI₃. Interestingly, the first studies on 2D perovskites can be dated back to the 1980s. The most popular 2D perovskites have a general formula of (RNH₃)₂MA _{n −1}M _n X_{3 n +1}, where n represents the number of metal halide octahedrons between the insulating organic cation layers. The optoelectronic properties of 2D perovskites, e.g., band gap, are highly dependent on the thickness of the inorganic layers (i.e., the value of n). Herein, 2D perovskites are arbitrarily divided into three classes, strict 2D (n = 1), quasi‐2D (n = 2–5), and quasi‐3D (n > 5), and research progress is summarized following this classification. The majority of existing 2D perovskites only employ very simple organic cations (e.g., butyl ammonium or phenylethyl ammonium), which merely function as the supporting layer/insulating barrier to achieve the 2D structure. Thus, a particularly important research question is: can functional organic cations be designed for these 2D perovskites, where these functional organic cations would play an important role in dictating the optoelectronic properties of these organic–inorganic hybrid materials, leading to unique device performance or applications?

Publication date: November 2018

Source: Nano Energy, Volume 53

Author(s): Yuanyuan Jiang, Congcong Wu, Liurui Li, Kai Wang, Zui Tao, Fan Gao, Weifeng Cheng, Jiangtao Cheng, Xin-Yan Zhao, Shashank Priya, Weiwei Deng

Abstract

Graphical abstract

Interface engineering in n‐i‐p metal halide perovskite solar cells is achieved by introducing 2D perovskites, functional molecules, quantum dots, and an insulating layer. Their roles include achieving better energy‐level alignment, passivating traps, resisting moisture and suppressing ion migration, contributing to improved performance, enhanced long‐term stability, and eliminated photocurrent hysteresis.

Recent years have witnessed continuous progress in metal halide perovskite (MHP) solar cells with a certified power conversion efficiency (PCE) exceeding 22%. However, the commercialization of MHP solar cells continues to encounter various challenges including stabilization, scalability and repeatability. Of all problems related to MHP materials, interface recombination is the most prominent, resulting in severe PCE loss within a short time. Fortunately, interface engineering has been identified as an efficient means of achieving better energy‐level alignment, reduced charge recombination, trap passivation, elimination of photocurrent hysteresis, and enhanced long‐term device stability. This review examines the relationship between specific interface modification layers and their roles in interface engineering based on device physics, revealed by several characterization methods. The latest research advances in interface modification layers according to their roles and properties are also summarized.

Films with composition continuously adjustable from pure SnS to SnO_x are fabricated using a facile anodization method, enabling improved photoelectrochemical and photocatalytic performance.

Anodic fabrication of tin sulfide is for the first time reported. Through a facile anodization method in a glycerol electrolyte of sodium sulfide, a range of interesting tin sulfide nanostructures are produced in a controllable manner. By changing the anodization parameters (anodization potential, water content, and electrolyte concentration), anodic nanomaterials ranging from pure SnS to SnO_x can be conveniently synthesized. The fabricated SnS/SnO_x multi‐heterojunction nanocomposites delivered greatly improved photoelectrochemical and photocatalytic performances, due to the presence of narrow‐bandgap SnS (≈1.56 eV) in wide‐bandgap SnO_x (≈3.6 eV), which can effectively separate the photoinduced electron‐hole pairs and prolong their lifetime. The novel method reported here presents an efficient strategy to directly construct metal sulfides or sulfide/oxide heterojunctions that are directly applicable as electrode materials in photoelectrochemical cells, photovoltaic devices, sensors, and binder‐free batteries or supercapacitors.

Intermolecular arrangements of PBDB‐T with ITIC and PC71BM are revealed by atomistic simulations. Owing to smaller side‐chain steric hindrance, both acceptors are prone to approach polymer A units, especially for ITIC considering better matching in size and shape. Importantly, PBDB‐T/ITIC docking occurs mainly via local π–π interaction between electron‐withdrawing end groups of ITIC and A units of the polymer, which is beneficial for efficient exciton dissociation.

Donor/acceptor (D/A) interfaces play a crucial role in photoelectric conversion for organic solar cells. However, it is impossible to experimentally probe D/A interfaces at the atomistic level to date, in particular for organic solar cells based on nonfullerene acceptors due to their anisotropic structures. In this work, we have investigated the interfacial structures of a representative D‐A copolymer donor PBDB‐T with a well‐known A‐D‐A structured nonfullerene acceptor ITIC, in comparison with a fullerene acceptor PC₇₁BM, by means of atomistic simulations. It is found that owing to different side‐chain steric hindrance between the polymer A and D units, both acceptors are more likely to approach the polymer A units, and more apparently for ITIC in consideration of the size and shape matching between the acceptors and the polymer A and D units. Importantly, docking of ITIC with polymer occurs mainly through local π–π interaction between the terminal moieties of ITIC and the A units of the polymer, and such interfacial structures are favorable for efficient exciton dissociation. Our work sheds light on the impact of side‐chain nature and location as well as acceptor structures on D/A interfaces and charge‐transfer dynamics, which will be very helpful for further improving the performance of organic photovoltaics.