Inkjet-printed SnO as an effective electron transport layer for planar perovskite solar cells and the effect of Cu doping.

Inkjet printing is a more sustainable and scalable fabrication method than spin coating for producing perovskite solar cells (PSCs). Although spin-coated SnO has been intensively studied as an effective electron transport layer (ETL) for PSCs, inkjet-printed SnO ETLs have not been widely reported. Here, we fabricated inkjet-printed, solution-processed SnO ETLs for planar PSCs. A champion efficiency of 17.55% was achieved for the cell using a low-temperature processed SnO ETL. The low-temperature SnO exhibited an amorphous structure and outperformed high-temperature crystalline SnO. The improved performance was attributed to enhanced charge extraction and transport and suppressed charge recombination at ETL/perovskite interfaces, which originated from enhanced electrical and optical properties of SnO, improved perovskite film quality, and well-matched energy level alignment between the SnO ETL and the perovskite layer. Furthermore, SnO was doped with Cu. Cu doping increased surface oxygen defects and upshifted energy levels of SnO, leading to reduced device performance. A tunable hysteresis was observed for PSCs with Cu-doped SnO ETLs, decreasing at first and turning into inverted hysteresis afterwards with increasing Cu doping level. This tunable hysteresis was related to the interplay between charge/ion accumulation and recombination at ETL/perovskite interfaces in the case of electron extraction barriers.