Strategies for Improving Efficiency and Stability of Perovskite Solar Cells
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Strategies for Improving Efficiency and Stability of Perovskite Solar Cells Xiaoli Zheng1,2, Yang Bai,2 Shuang Xiao,2 Xiangyue Meng,2 Teng Zhang2 and Shihe Yang2* 1 College of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450052, China. 2 Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong. *corresponding author email: [email protected] ABSTRACT Perovskite solar cells (PSCs) based on organometal halide light absorbers have hit the limelight in recent years owing to their low temperature solution processability, material abundance and rapidly rising efficiency. To rival the leading photovoltaic technologies, efficiency and long-term stability of PSCs represent two prime facets of the challenges currently facing the research community. Herein we summarize the strategies for improving efficiency and stability of PSCs by drawing on our recent work. Emphasis is given to the importance of perovskite film growth, electron/hole transport materials and interface materials in cell performance. We also discuss possible degradation mechanisms of PSCs. INTRODUCTION Over the past few years, organometallic halide perovskite solar cells (PSCs) have sprung to the forefront of photovoltaic research [1-5]. Thanks to the high absorption coefficient, tunable band gap, long carrier diffusion lengths, abundant elemental constituents and low temperature processing advantages, the PSCs have undergone a rapid rise in power conversion efficiency (PCE) to over 22% certified [6-9]. According to the device structure, the core components of PSCs are perovskite light absorbers and electron/hole extraction/transport materials, which are responsible for light absorption, charge separation and charge transport, respectively [10]. It is generally accepted that obtaining a high-quality of perovskite layer and electron/hole extraction/transport layers alongside suitable interface layers is a prerequisite to high performance PSCs. To improve the efficiency and stability of PSCs, several methods were utilized to promote the perovskite film quality, including mixed solvent [11], toluene drop-casting [12], solvent extraction [13], solvent-vapor-assisted annealing [14], etc. Li et al. first used a vacuum-flash-assisted solution processing method to obtain shiny, smooth and crystalline perovskite film of high electronic quality over layer areas [9]. However, the working mechanisms of these methods are often poorly understood, especially for the mechanism of solvent vapor annealing assisting-high quality perovskite growth [15,16]. Moreover, the choice of appropriate electron/hole extraction/transport materials is another big issue. By far, various organic and inorganic materials, such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), spiro-OMeTAD, Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), titanium oxide (TiO2), Tin oxide (SnO2), nickel oxide (NiO), have been exclusively used in the PSCs as electron/hole
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