Defects engineering for high-performance perovskite solar cells

npj Flexible Electronics, Aug 2018

Metal halide perovskites have achieved great success in photovoltaic applications during the last few years. The solar to electrical power conversion efficiency (PCE) of perovskite solar cells has been rapidly improved from 3.9% to certified 22.7% due to the extensive efforts on film deposition methods, composition and device engineering. Further investigation on eliminating the defect states in perovskite absorbers is necessary to push forward the PCE of perovskite solar cells approaching the Shockley-Queisser limit. In this review, we summarize the defect properties in perovskite films and present methodologies to control the defects density, including the growth of large size crystals, photo-curing method, grain boundary and surface passivation, and modification of the substrates. We also discuss the defects-related stability and hysteresis issues and highlight the current challenges and opportunities in defects control of perovskite films.

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Defects engineering for high-performance perovskite solar cells

Abstract Metal halide perovskites have achieved great success in photovoltaic applications during the last few years. The solar to electrical power conversion efficiency (PCE) of perovskite solar cells has been rapidly improved from 3.9% to certified 22.7% due to the extensive efforts on film deposition methods, composition and device engineering. Further investigation on eliminating the defect states in perovskite absorbers is necessary to push forward the PCE of perovskite solar cells approaching the Shockley-Queisser limit. In this review, we summarize the defect properties in perovskite films and present methodologies to control the defects density, including the growth of large size crystals, photo-curing method, grain boundary and surface passivation, and modification of the substrates. We also discuss the defects-related stability and hysteresis issues and highlight the current challenges and opportunities in defects control of perovskite films. Introduction Metal halide perovskites with the formula of ABX3 (where A is an organic or cesium cation, B is a lead or tin cation and X is a halide anion) have achieved an undeniable breakthrough on photovoltaic development. The power conversion efficiency (PCE) of perovskite solar cells has rapidly rocketed from 3.9% to certified 22.7% during the past few years.1,2,3,4,5(https://www.nrel.gov/pv/assets/images/efficiency-chart.png). The impressive PCE increase can be attributed to their superior optoelectronic properties, including strong absorption coefficient (~105 cm−1), low exciton binding energy (~20 meV), and relatively long carrier diffusion length (>1 μm).6,7 In addition, a wide range of solution processing techniques, including one-step deposition,8 two-steps sequential deposition,4 solvent-quenching,9 and other modified approaches based on these methods have been developed to fabricate uniform and high-crystalline perovskite films, resulting in the fast rising in the device performance. Furthermore, composition engineering of perovskite materials from the basic methylammonium lead triiodide (MAPbI3, CH3NH3PbI3) perovskite to current mixed-cation and mixed-anion halide perovskites lead to high-efficiency and improved stability.5,10,11,12 Despite the rapid progress, the device performance of perovskite solar cells is still far from their theoretical limits. A key factor to further improve the efficiency of perovskite solar cells is to develop high-quality perovskite active layers with further reduced defect density and less nonradiative recombination processes. Recently, a certified efficiency of 22.1% has been achieved by introducing additional triiodide ions during the formation of perovskite films to suppress the formation of deep-level defects.5 Along with the rapid progress of perovskite solar cells, some review articles have been published covering various critical aspects with particular focuses on the film deposition and device engineering,13,14,15,16 photophysical properties,17,18,19,20,21 interfacial materials,21,22,23,24 long-term stability,25,26,27,28 and toxicity.29,30,31 However, to the best of our knowledge, few reviews systematically discussed the achievements in addressing the defects in perovskites, including defects at the surface or in the bulk films. In this review, we briefly introduce the effects of defects in polycrystalline perovskite films on the device performance of perovskite solar cells. We summarize the achievements that have been made in the field of defects engineering investigations. We focus on the methodologies on reducing the defect states of metal halide perovskites, including efforts on crystal growth, post treatments, and interfacial modifications. We anticipate that this review will spur new strategies for defects control of perovskites, leading to perovskite solar cells with further improved efficiency and long-term stability beyond the state-of-the-art. Effects of defects in perovskite films and the device performance of solar cells Although the metal halide perovskites have shown high defect-tolerance, it is now generally accepted that there are still deep defects in perovskite thin films that hinder the PCE of perovskite solar cells approaching the Schockley-Queisser limit.32,33 In this section, we will simply talk about the defect properties in perovskite films and their influence on device performance. It is known that defects in the light-harvesting layer influence the device performance metrics of the ensuing solar cells. To get a deep understanding of defects in metal halide perovskites, we refer the reader to a very informative review given by Ball and co-workers focusing on the origin and nature of defects in halide perovskite semiconductors and their impacts on the active layer and the obtained solar cells.20 According to previous calculation and experimental results, the nature and density of defect states in perovskites is highly sensitive to the film deposition conditions.34 For exam (...truncated)


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Feng Wang, Sai Bai, Wolfgang Tress, Anders Hagfeldt, Feng Gao. Defects engineering for high-performance perovskite solar cells, npj Flexible Electronics, 2018, Issue: 2, DOI: 10.1038/s41528-018-0035-z