Thermally evaporated two-dimensional SnS as an efficient and stable electron collection interlayer for inverted planar perovskite solar cells

Hybrid organic-inorganic perovskite solar cells (PSCs) have attracted significant attention because of their advantages of a high power conversion efficiency and low fabrication cost. Their efficiencies have skyrocketed from 3% to over 22% just within few years of research. Interlayer engineering is an efficient method for further improving the performance of planar perovskite solar cells. There are two types of materials widely applied for interfaces. Organic interlayers can be easily processed, yet they have lower stability under light or at elevated temperatures. Metal oxide interlayers require costlier and, more importantly, higher temperature processing methods which lead to degradation of the underlying perovskite layer. In this work, we propose tin(ii) sulfide (SnS), a IV-VI semiconductor, as an interlayer material to replace bathocuproine (BCP) for electron collection. The deposition of the interlayer is achieved by thermal evaporation, and the power conversion efficiency (PCE) of the optimized device reached up to 18.40%. With a comparable PCE and improved stability, SnS can replace BCP successfully. Additionally, we explored devices with fully inorganic interlayers by employing a metal oxide as the hole transport interlayer. This method further increased the stability.