ZHANG JIAJIA

A series of copolymers via a random copolymerization approach are designed and synthesized. The well‐defined fibril interpenetrating morphology with appropriate phase separation in PT2‐based blends can efficiently suppress the unfavorable aggregation, resulting in excellent morphological stability and high efficiency. The work demonstrates the importance of optimization of fibril network morphology in realizing high‐efficiency and ambient‐stable polymer solar cells.

Abstract

Morphological stability is crucially important for the long‐term stability of polymer solar cells (PSCs). Many high‐efficiency PSCs suffer from metastable morphology, resulting in severe device degradation. Here, a series of copolymers is developed by manipulating the content of chlorinated benzodithiophene‐4,8‐dione (T1‐Cl) via a random copolymerization approach. It is found that all the copolymers can self‐assemble into a fibril nanostructure in films. By altering the T1‐Cl content, the polymer crystallinity and fibril width can be effectively controlled. When blended with several nonfullerene acceptors, such as TTPTT‐4F, O‐INIC3, EH‐INIC3, and Y6, the optimized fibril interpenetrating morphology can not only favor charge transport, but also inhibit the unfavorable molecular diffusion and aggregation in active layers, leading to excellent morphological stability. The work demonstrates the importance of optimization of fibril network morphology in realizing high‐efficiency and ambient‐stable PSCs, and also provides new insights into the effect of chemical structure on the fibril network morphology and photovoltaic performance of PSCs.

Applied Physics Letters, Volume 117, Issue 4, July 2020.
This study elucidated the influence of a nickel oxide inorganic hole transporting layer and its by-products produced with and without additives on planar MAPbI3 perovskite solar cell performance. We found out that NiO films produced from additive-free solution demonstrate a higher concentration of by-products in the form of Ni(OH)2. The additives enhanced the NiO concentration in final films, reducing the Ni(OH)2 concentration and improving morphology and crystallinity of the upper perovskite layer. The possible chemical reactions for NiO formation with and without additives were proposed and proved by the results of XPS and Zeta potential studies. After adding additives, with the decrease in the Ni(OH)2 concentration, the amount of by-product NiOOH had been increased, and both Ni(OH)2 and NiOOH influence the final amount of NiO in the resulting films. The effects of the NiO concentration and additives such as ethanolamine, diethanolamine, and triethanolamine have been studied for the planar MAPbI3 perovskite solar cell performance. The best devices based on additive-free NiO films of 25 mg/ml concentration exhibited a power conversion efficiency of 11.02%, while NiO with diethanolamine additive films demonstrated a power conversion efficiency of 15.4%.

The M13 bacteriophage functions as an effective perovskite growth template and a passivator in perovskite solar cells. This is owing to its filamentous and uniform dimension, as well as the amino acids on its surface. These effects enhance when the M13 viruses are denatured at high temperature. The efficiency increases from 17.8% to 20.1% upon addition of the denatured viruses.

Abstract

The M13 bacteriophage, a nature‐inspired environmentally friendly biomaterial, is used as a perovskite crystal growth template and a grain boundary passivator in perovskite solar cells. The amino groups and carboxyl groups of amino acids on the M13 bacteriophage surface function as Lewis bases, interacting with the perovskite materials. The M13 bacteriophage‐added perovskite films show a larger grain size and reduced trap‐sites compared with the reference perovskite films. In addition, the existence of the M13 bacteriophage induces light scattering effect, which enhances the light absorption particularly in the long‐wavelength region around 825 nm. Both the passivation effect of the M13 bacteriophage coordinating to the perovskite defect sites and the light scattering effect intensify when the M13 virus‐added perovskite precursor solution is heated at 90 °C prior to the film formation. Heating the solution denatures the M13 bacteriophage by breaking their inter‐ and intra‐molecular bondings. The denatured M13 bacteriophage‐added perovskite solar cells exhibit an efficiency of 20.1% while the reference devices give an efficiency of 17.8%. The great improvement in efficiency comes from all of the three photovoltaic parameters, namely short‐circuit current, open‐circuit voltage, and fill factor, which correspond to the perovskite grain size, trap‐site passivation, and charge transport, respectively.

Publication date: 16 September 2020

Source: Joule, Volume 4, Issue 9

Author(s): Haoran Wang, Xiwen Gong, Dewei Zhao, Yong-Biao Zhao, Sheng Wang, Jianfeng Zhang, Lingmei Kong, Bin Wei, Rafael Quintero-Bermudez, Oleksandr Voznyy, Yuequn Shang, Zhijun Ning, Yanfa Yan, Edward H. Sargent, Xuyong Yang

Publication date: 16 September 2020

Source: Joule, Volume 4, Issue 9

Author(s): Yehao Deng, Zhenyi Ni, Axel F. Palmstrom, Jingjing Zhao, Shuang Xu, Charles H. Van Brackle, Xun Xiao, Kai Zhu, Jinsong Huang

Nature Reviews Materials, Published online: 29 July 2020; doi:10.1038/s41578-020-0221-1

The surface features of metal halide perovskites have a crucial role in determining their properties. This Review introduces the recent advances in the understanding of perovskite surfaces and surveys the surface strategies towards improving the properties of perovskite materials and the performance of perovskite optoelectronic devices.

Publication date: 17 June 2020

Source: Joule, Volume 4, Issue 6

Author(s): Aobo Ren, Huagui Lai, Xia Hao, Zeguo Tang, Hao Xu, Bernice Mae F. Yu Jeco, Kentaroh Watanabe, Lili Wu, Jingquan Zhang, Masakazu Sugiyama, Jiang Wu, Dewei Zhao

A design of halide perovskites (HP) for use in resistive switching memory (RSM) by combining first‐principles screening and experimental verification is conducted. First‐principles calculations identify 2D HP structure (AB₂X₅) as the best candidate for RSM. To verify the calculation results, 2D‐layered CsPb₂Br₅ is synthesized and applied to RSM. The CsPb₂Br₅‐based RSM shows stable operation with low operating voltages.

Abstract

Memory devices have been advanced so much, but still it is highly required to find stable and reliable materials with low‐power consumption. Halide perovskites (HPs) have been recently adopted for memory application since they have advantages of fast switching based on ionic motion in crystal structure. However, HPs also suffer from poor stability, so it is necessary to improve the stability of HPs. In this regard, combined first‐principles screening and experimental verification are performed to design HPs that have high environmental stability and low‐operating voltage for memory devices. First‐principles screening identifies 2D layered AB₂X₅ structure as the best candidate switching layer for memory devices, because it has lower formation energy and defect formation energy than 3D ABX₃ or other layered structures (A₃B₂X₇, A₂BX₄). To verify results, all‐inorganic 2D layered CsPb₂Br₅ is synthesized and used in memory devices. The memory devices that use CsPb₂Br₅ show much better stability and lower operating voltages than devices that use CsPbBr₃. These findings are expected to provide new opportunity to design materials for reliable device applications based on calculation, screening, and experimental verification.

Applied Physics Letters, Volume 116, Issue 25, June 2020.
CH3NH3PbI3 (MAPbI3)-based perovskite solar cells (PSCs) with special hole and electron transport layers (HTL and ETL) were prepared to study their light-induced degradation. Obvious degradation was observed under initial light exposure not only at the device level but also at the film morphology and electronic structure level. Device performance parameters, such as short-circuit current (JSC), power conversion efficiency, fill factor, and hysteresis effect, were aggravated with an initial light exposure of less than ∼8 h at 1 sun intensity. Meanwhile, the deteriorated crystallinity and electronic structure of the MAPbI3 film were also detected with x-ray diffraction, ultraviolet photoelectron spectroscopy, and UV-Visible absorption spectroscopy. The observed degradation is rationally related to the light-induced decomposition of MAPbI3. However, the degradation can be partly recovered with the following light exposure resulting in self-healing of the devices and MAPbI3 films. The self-healing behavior should be ascribed to the conversion of decomposition products back to MAPbI3, because the intermediates are wrapped tightly in the photoactive layer by the compact coverlayers of HTLs and ETLs and some reversible reactions occur consequently. The mechanism of self-healing is discussed by introducing the trapped states derived from ion migration. The PSCs prepared here imply a good optical stability and thus a good performance facilitated by tight wrapping of the active MAPbI3.

Applied Physics Letters, Volume 116, Issue 26, June 2020.
CH3NH3PbI3 (MAPbI3) perovskite materials hold considerable promise for future low cost, high-efficiency solar cells, and replacement materials for toxic lead have also been in demand. In this study, the optical constants, absorption coefficients, and interband electron transitions of MAPb1−xSnxI3 (x = 0, 0.4, 0.8, and 1) films have been analyzed by spectroscopic ellipsometry in the photon range of 1 eV–5 eV. The bandgaps of MAPb1-xSnxI3 (x = 0, 0.4, 0.8, 1) are 1.54 eV, 1.51 eV, 1.49 eV, and 1.46 eV, respectively. With the increase in Sn, the s–p antibonding coupling becomes stronger, and the bandgap energy decreases, owing to the shallower and more active lone-pair states of Sn-5s than Pb-5s near the valence band maximum (VBM). According to the x-ray diffraction patterns, doping Sn does not change the material structures, which makes the shape of VBM more fluctuating, resulting in a similar band structure. Moreover, band structures and interband electron transitions of all four samples are discussed in terms of solid-state physics and can be assigned to the direct transition between the valence band and the conduction band at R, M, and X symmetry points.

This work reports a compatible strategy to enhance the efficiency of planar n–i–p Sb₂Se₃ solar cells through Sb₂Se₃ surface modification and an architecture with oriented 1D van der Waals material, trigonal selenium (t‐Se). The p‐type t‐Se layer functionally works as a surface passivation and hole transport material. The all‐inorganic device structure enables high efficiency and superb stability.

Abstract

Environmentally benign and potentially cost‐effective Sb₂Se₃ solar cells have drawn much attention by continuously achieving new efficiency records. This article reports a compatible strategy to enhance the efficiency of planar n–i–p Sb₂Se₃ solar cells through Sb₂Se₃ surface modification and an architecture with oriented 1D van der Waals material, trigonal selenium (t‐Se). A seed layer assisted successive close spaced sublimation (CSS) is developed to fabricate highly crystalline Sb₂Se₃ absorbers. It is found that the Sb₂Se₃ absorber exhibits a Se‐deficient surface and negative surface band bending. Reactive Se is innovatively introduced to compensate the surface Se deficiency and form an (101) oriented 1D t‐Se interlayer. The p‐type t‐Se layer promotes a favored band alignment and band bending at the Sb₂Se₃/t‐Se interface, and functionally works as a surface passivation and hole transport material, which significantly suppresses interface recombination and enhances carrier extraction efficiency. An efficiency of 7.45% is obtained in a planar Sb₂Se₃ solar cell in superstrate n–i–p configuration, which is the highest efficiency for planar Sb₂Se₃ solar cells prepared by CSS. The all‐inorganic Sb₂Se₃ solar cell with t‐Se shows superb stability, retaining ≈98% of the initial efficiency after 40 days storage in open air without encapsulation.

Publication date: 15 July 2020

Source: Joule, Volume 4, Issue 7

Author(s): Qin Hu, Wei Chen, Wenqiang Yang, Yu Li, Yecheng Zhou, Bryon W. Larson, Justin C. Johnson, Yi-Hsien Lu, Wenkai Zhong, Jinqiu Xu, Liana Klivansky, Cheng Wang, Miquel Salmeron, Aleksandra B. Djurišić, Feng Liu, Zhubing He, Rui Zhu, Thomas P. Russell

Nature Chemistry, Published online: 06 July 2020; doi:10.1038/s41557-020-0488-2

The strength of electrostatic interactions in semiconductors strongly affects their performance in optoelectronic devices. Now, doping two-dimensional naphthalene-based lead halide perovskites with tetrachloro-1,2-benzoquinone has been shown to introduce donor–acceptor interactions within the organic network, without disrupting the inorganic sublattice. This in turn altered the energy of the materials’ electron–hole electrostatic Coulomb interactions.

Publication date: 19 August 2020

Source: Joule, Volume 4, Issue 8

Author(s): Caleb C. Boyd, R. Clayton Shallcross, Taylor Moot, Ross Kerner, Luca Bertoluzzi, Arthur Onno, Shalinee Kavadiya, Cullen Chosy, Eli J. Wolf, Jérémie Werner, James A. Raiford, Camila de Paula, Axel F. Palmstrom, Zhengshan J. Yu, Joseph J. Berry, Stacey F. Bent, Zachary C. Holman, Joseph M. Luther, Erin L. Ratcliff, Neal R. Armstrong

Applied Physics Letters, Volume 117, Issue 1, July 2020.
Nonradiative charge recombination is the main restriction on the high efficiency of organic–inorganic hybrid perovskite solar cells (PVSCs). The synergistic manipulation of the grain boundary/interface traps can control charge behavior and improve device performance. In our work, the composition of perovskite used is FA0.8MA0.15Cs0.05PbI2.8Br0.2 (MA is methylammonium, FA is formamidinium), which produces high-performing PVSCs. A trace additive of n-butylammonium bromide (BABr) was incorporated into the perovskite precursor to passivate grain–boundary defects. The NH4Cl/KCl was spin-coated onto the electron-transport layer to modify interface contact and impede nonradiative charge recombination, inducing a high power-conversion efficiency (PCE). The highest-performing PVSCs achieved a PCE of 21.02%, a Voc of 1.13 V, a Jsc of 23.55 mA cm−2, and a FF of 0.79 under a reverse voltage scan (under a forward voltage scan the values were as follows: PCE, 20.13%; Voc, 1.12 V; Jsc, 23.65 mA cm−2; FF, 0.76), with a negligible J–V hysteresis. The hybrid 2D/3D perovskite heterostructure formed through the incorporation of BABr increased crystallinity and mitigated nonradiative recombination, resulting in reduced current-voltage hysteresis, enhanced efficiency, and significantly improved operational stability. With impedance spectroscopy and time-resolved surface photovoltage spectroscopy, the charge dynamics in PVSCs were determined.

Nature Nanotechnology, Published online: 13 July 2020; doi:10.1038/s41565-020-0729-y

The realization of high-quality van der Waals contacts on monocrystalline halide perovskite thin films enables the probing of their long-range carrier and photocarrier transport properties.

Publication date: 19 August 2020

Source: Joule, Volume 4, Issue 8

Author(s): Lingeswaran Arunagiri, Zhengxing Peng, Xinhui Zou, Han Yu, Guangye Zhang, Zhen Wang, Joshua Yuk Lin Lai, Jianquan Zhang, Yan Zheng, Chaohua Cui, Fei Huang, Yingping Zou, Kam Sing Wong, Philip C.Y. Chow, Harald Ade, He Yan

Publication date: 15 July 2020

Source: Joule, Volume 4, Issue 7

Author(s): Lik-Kuen Ma, Yuzhong Chen, Philip C.Y. Chow, Guangye Zhang, Jiachen Huang, Chao Ma, Jianquan Zhang, Hang Yin, Andy Man Hong Cheung, Kam Sing Wong, Shu Kong So, He Yan

Publication date: 15 January 2020

Source: Joule, Volume 4, Issue 1

Author(s): Jiahuan Zhang, Zaiwei Wang, Aditya Mishra, Maolin Yu, Mona Shasti, Wolfgang Tress, Dominik Józef Kubicki, Claudia Esther Avalos, Haizhou Lu, Yuhang Liu, Brian Irving Carlsen, Anand Agarwalla, Zishuai Wang, Wanchun Xiang, Lyndon Emsley, Zhuhua Zhang, Michael Grätzel, Wanlin Guo, Anders Hagfeldt

Publication date: 15 January 2020

Source: Joule, Volume 4, Issue 1

Author(s): Chuang-Yi Liao, Yao Chen, Chun-Chieh Lee, Gang Wang, Nai-Wei Teng, Chia-Hao Lee, Wei-Long Li, Yu-Kuang Chen, Chia-Hua Li, Hsiuan-Lin Ho, Phoebe Huei-Shuan Tan, Binghao Wang, Yu-Chin Huang, Ryan M. Young, Michael R. Wasielewski, Tobin J. Marks, Yi-Ming Chang, Antonio Facchetti