吴晓晓

Publication date: June 2021

Source: Nano Energy, Volume 84

Author(s): Jian Xiong, Zhongjun Dai, Shiping Zhan, Xiaowen Zhang, Xiaogang Xue, Weizhi Liu, Zheling Zhang, Yu Huang, Qilin Dai, Jian Zhang

Publication date: June 2021

Source: Nano Energy, Volume 84

Author(s): Dongxu Lin, Xin Xu, Tiankai Zhang, Nana Pang, Jiming Wang, Huanyong Li, Tingting Shi, Ke Chen, Yang Zhou, Xin Wang, Jianbin Xu, Pengyi Liu, Weiguang Xie

Two‐dimensional (2D) organic–inorganic hybrid perovskites perform photocatalytic H₂ production more efficiently than their 3D counterparts in spite of the higher exciton binding energy and inferior light absorption. The length of the organic cations of 2D perovskites influences the optoelectronic and charge transfer properties, and the perovskite with the shortest organic cation length achieved the benchmark solar energy conversion efficiency.

Abstract

Three‐dimensional (3D) organic–inorganic hybrid perovskites have demonstrated excellent capability in solar fuel production, while the two‐dimensional (2D) counterparts are generally considered inferior candidates due to the high exciton binding energy and weak light absorption. Herein, contrary to our common understanding, we find that 2D perovskites can perform photocatalytic H₂ production from HI splitting more efficiently than their 3D counterparts. We observed sharp difference between 2D perovskites crystals with organic phenylalkylammonium cations of different lengths and the 3D counterparts in their stabilization behavior in aqueous solution. Moreover, we show that the organic cations length of the 2D perovskites affects the nanostructures, optoelectronic properties, and the charge transfer process significantly, which determines the photocatalytic activity of the 2D perovskites. Among the 2D perovskites under investigation, phenylmethylammonium lead iodide with the shortest organic cations achieved the best solar‐to‐chemical conversion efficiency of ca. 1.57 %, which is the highest value ever reported for hybrid perovskites.

This Minireview describes developments in all‐polymer solar cells containing a new type of n‐type conjugated polymer, polymerized small‐molecule acceptors (PSMAs). PSMAs combine the merits of small‐molecule acceptors (narrow band gap, strong absorption, and suitable electronic energy levels) with the good film formation, higher morphology and light‐irradiation stability of polymers.

Abstract

All‐polymer solar cells (all‐PSCs) have drawn tremendous research interest in recent years, due to their inherent advantages of good film formation, stable morphology, and mechanical flexibility. The most representative and most widely used n‐CP acceptor was the naphthalene diimide based D‐A copolymer N2200 before 2017, and the power conversion efficiency (PCE) of the all‐PSCs based on N2200 reached over 8% in 2016. However, the low absorption coefficient of N2200 in the near‐infrared (NIR) region limits the further increase of its PCE. In 2017, we proposed a strategy of polymerizing small‐molecule acceptors (SMAs) to construct new‐generation polymer acceptors. The polymerized SMAs (PSMAs) possess low band gap and strong absorption in the NIR region, which attracted great attention and drove the PCE of the all‐PSCs to over 15% recently. In this Minireview we explain the design strategies of the molecular structure of PSMAs and describe recent research progress. Finally, current challenges and future prospects of the PSMAs are analyzed and discussed.

A 2D ice‐templating approach has been developed to assemble silver nanowires (AgNW) into large‐area patterns for a high‐performance flexible transparent electrode. The excellent alignment of AgNW pattern provides a high contact area, yielding a high optical transmittance (≈91%) and low sheet resistance (20 Ω sq⁻¹) simultaneously with a relatively low dosage of AgNWs (4 µg cm⁻²). More importantly, it is believed that this 2D ice‐templating approach is versatile to assemble various building blocks into large‐area patterns with designable topology and function, which are strongly demanded for advanced electronic devices.

Abstract

Flexible transparent electrodes are critically important for the emerging flexible and stretchable electronic and optoelectronic devices. To this end, transparent polymer films coated with silver nanowires (AgNWs) have been intensively studied in the past decade. However, it remains a grand challenge to achieve both high conductivity and transmittance in large‐area films, mainly due to the poor alignment of AgNWs and their high junction resistance. Here, the successful attempt to realize large‐area AgNW patterns on various substrates by a 2D ice‐templating approach is reported. With a relatively low dosage of AgNWs (4 µg·cm⁻²), the resulted flexible electrode simultaneously achieves high optical transmittance (≈91%) and low sheet resistance (20 Ω·sq⁻¹). In addition, the electrode exhibits excellent durability during cyclic bending (≈10 000 times) and stretching (50% strain). The potential applications of the flexible transparent electrode in both touch screen and electronic skin sensor, which can monitor the sliding pressure and direction in real‐time, are demonstrated. More importantly, it is believed that the study represents a facile and low‐cost approach to assemble various nanomaterials into large‐area functional patterns for advanced flexible devices.

The current developments and advanced understanding of polarization‐sensitive halide perovskites are comprehensively reviewed, involving linear/circular polarization luminescence and detection. Also, the key challenges and current opportunities in the field are discussed. The great promise of polarization‐sensitive halide perovskites is addressed to inspire other potential applications in opotoelectronics.

Abstract

While halide perovskites (HPs) have achieved enormous success in the field of optoelectronic applications, much attention has been recently drawn to the unique polarization sensitivity of HPs, either intrinsic or extrinsic, which makes HPs a potential candidate for innovative applications in directly polarized luminescence and detection. Herein, the research status in the field of polarization‐sensitive HPs, including linear polarization and circular polarization, is comprehensively summarized. To evaluate the effectiveness of HPs in generating and detecting linearly or circularly polarized light, the principles and characterization methods of polarized luminescence and detection are introduced. Sequentially, the state‐of‐the‐art development of the strategies that induce the linear or circular polarization characteristics of HPs is systematically reviewed, based on which the application of polarization‐sensitive HPs in the field of polarization luminescence and detection are summarized. Moreover, the current challenges and opportunities are discussed, and prospects of the future development in this promising field are outlined.

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.

Blending the organic semiconductor 2,7‐dioctyl[1]benzothieno[3,2‐b]benzothiophene (C₈‐BTBT) with the layered Ruddlesden–Popper‐phase perovskite (PEA)₂PbBr₄ in solution phase facilitates the formation of large and near‐single‐crystalline‐quality platelet‐like perovskite domains overlaid by a thin layer of the organic molecule. Transistors utilizing the (PEA)₂PbBr₄/C₈‐BTBT bilayer as the channel exhibit unexpectedly large hysteresis, and their use as a non‐volatile memory element is demonstrated.

Abstract

Controlling the morphology of metal halide perovskite layers during processing is critical for the manufacturing of optoelectronics. Here, a strategy to control the microstructure of solution‐processed layered Ruddlesden–Popper‐phase perovskite films based on phenethylammonium lead bromide ((PEA)₂PbBr₄) is reported. The method relies on the addition of the organic semiconductor 2,7‐dioctyl[1]benzothieno[3,2‐b]benzothiophene (C₈‐BTBT) into the perovskite formulation, where it facilitates the formation of large, near‐single‐crystalline‐quality platelet‐like (PEA)₂PbBr₄ domains overlaid by a ≈5‐nm‐thin C₈‐BTBT layer. Transistors with (PEA)₂PbBr₄/C₈‐BTBT channels exhibit an unexpectedly large hysteresis window between forward and return bias sweeps. Material and device analysis combined with theoretical calculations suggest that the C₈‐BTBT‐rich phase acts as the hole‐transporting channel, while the quantum wells in (PEA)₂PbBr₄ act as the charge storage element where carriers from the channel are injected, stored, or extracted via tunneling. When tested as a non‐volatile memory, the devices exhibit a record memory window (>180 V), a high erase/write channel current ratio (10⁴), good data retention, and high endurance (>10⁴ cycles). The results here highlight a new memory device concept for application in large‐area electronics, while the growth technique can potentially be exploited for the development of other optoelectronic devices including solar cells, photodetectors, and light‐emitting diodes.

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.

Photodetectors (PDs) based on low‐dimensional metal halide perovskites (MHPs) have attracted burgeoning interest for next‐generation optoelectronic applications. Recent advances in low‐dimensional MHP‐based PDs are summarized, including the synthesis, fundamental properties, performance, and stability issues. By discussing practical strategies and existing challenges, perspectives on low‐dimensional MHP PDs for improved future performance and stability are provided.

Abstract

Metal halide perovskites (MHPs) have been a hot research topic due to their facile synthesis, excellent optical and optoelectronic properties, and record‐breaking efficiency of corresponding optoelectronic devices. Nowadays, the development of miniaturized high‐performance photodetectors (PDs) has been fueling the demand for novel photoactive materials, among which low‐dimensional MHPs have attracted burgeoning research interest. In this report, the synthesis, properties, photodetection performance, and stability of low‐dimensional MHPs, including 0D, 1D, 2D layered and nonlayered nanostructures, as well as their heterostructures are reviewed. Recent advances in the synthesis approaches of low‐dimensional MHPs are summarized and the key concepts for understanding the optical and optoelectronic properties related to the PD applications of low‐dimensional MHPs are introduced. More importantly, recent progress in novel PDs based on low‐dimensional MHPs is presented, and strategies for improving the performance and stability of perovskite PDs are highlighted. By discussing recent advances, strategies, and existing challenges, this progress report provides perspectives on low‐dimensional MHP‐based PDs in the future.

Publication date: June 2021

Source: Nano Energy, Volume 84

Author(s): Jiehao Fu, Haiyan Chen, Peihao Huang, Qingqing Yu, Hua Tang, Shanshan Chen, Sungwoo Jung, Kuan Sun, Changduk Yang, Shirong Lu, Zhipeng Kan, Zeyun Xiao, Gang Li

Publication date: June 2021

Source: Nano Energy, Volume 84

Author(s): Hailiang Wang, Huicong Liu, Zijing Dong, Weiping Li, Liqun Zhu, Haining Chen