Lawrence Berkeley National Laboratory

Inkjet printing is a more sustainable and scalable fabrication method than spin coating for producing perovskite solar cells (PSCs). Although spin-coated SnO₂ has been intensively studied as an effective electron transport layer (ETL) for PSCs, inkjet-printed SnO₂ ETLs have not been widely reported. Here, we fabricated inkjet-printed, solution-processed SnO_x ETLs for planar PSCs. A champion efficiency of 17.55% was achieved for the cell using a low-temperature processed SnO_x ETL. The low-temperature SnO_x exhibited an amorphous structure and outperformed high-temperature crystalline SnO₂. 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_x, improved perovskite film quality, and well-matched energy level alignment between the SnO_x ETL and the perovskite layer. Furthermore, SnO_x was doped with Cu. Cu doping increased surface oxygen defects and upshifted energy levels of SnO_x, leading to reduced device performance. A tunable hysteresis was observed for PSCs with Cu-doped SnO_x 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.