Progress and Perspective of Tin Perovskite Solar Cells

Abstract

Since organic-inorganic halide perovskites were first used in the field of solar cells in 2009, they have emerged as the most promising high-efficiency and low-cost next-generation solar cells. However, even though conventional lead perovskite halide perovskite solar cells have achieved a record efficiency of 25.2%, there is scope for improvement in terms of the detrimental properties of their constituent heavy metals. In addition, their theoretic efficiencies are limited by the large bandgap. Tin perovskite has received considerable attention in recent years, due to its heavy-metal-free character and superior semiconductor properties, such as a suitable bandgap and a high carrier mobility. In order to fabricate tin perovskite solar cells (TPSCs) of high-efficiency, the major obstacles have to be overcome, including fast crystallization of tin perovskites, high p-type carrier concentration, and high defect density. Even if Sn2+ has similar electronic configuration as Pb2+, Sn2+ has two more active electrons, which render tin perovskite less stable. To deal with these problems many strategies are developed. Lewis bases, such as dimethyl sulfoxide, are widely used to slow down the crystallization rate of tin perovskite, while oxide protective layer and plentiful additives (e.g., SnF2, liquid formic acid, and hydrazine vapor) have been found to reduce their oxidation. Furthermore, low-dimension structure and device engineering have been verified effectively promote TPSCs performance. Owing to the aforementioned strategies, the efficiency and stabilities of TPSCs were improving rapidly over the past few years, which indicates that TPSCs are the most promising candidate of lead-free perovskite solar cells. Recently, the certified efficiency of TPSCs reached over 12%, which is the maximum value for lead-free perovskite solar cells. Herein, we discuss the crystal and band structures, as well as the optoelectronic properties of tin perovskites. Furthermore, recent representative studies on tin perovskite are introduced, along with the strategies employed to improve the conversion efficiency, including the achievements based on component modification, dimension control, crystallization engineering and device structure design. Finally, we highlight the challenges presented by tin perovskites and the possible paths to improve device performance.