Recent progress in electron transport layers for efficient perovskite solar cells

Thin-film photovoltaics based on organic–inorganic hybrid perovskite light absorbers have recently emerged as a promising low-cost solar energy harvesting technology. Over the past several years, we have witnessed a great and unexpected progress in organic–inorganic perovskite solar cells (PSCs). The power conversion efficiency (PCE) increased from 3.8% to 20.1% and exceeded the highest efficiency of conventional dye-sensitized solar cells. Here, the focus is specifically on the recent developments of the electron transport layer (ETL) in PSCs, which is an important part for high performing PSCs. This review briefly discusses the development of the structure of PSCs, and we attempt to give a systematic introduction about the optimization of ETL and its related interfaces for efficient PSCs. Moreover, the introduction of appropriate interfacial materials is another important issue to improve PSC performance by optimizing the interfacial electronic properties between the perovskite layer and the charge-collecting electrode. Besides, some related issues such as device stability and hysteresis behavior are also discussed here.