Polyelectrolyte‐Doped SnO 2 as a Tunable Electron Transport Layer for High‐Efficiency and Stable Perovskite Solar Cells

The charge transport layer is crucial to the performance and stability of the perovskite solar cells (PSCs). Compared with other conventional metal oxide electron transport materials, SnO 2 has a deeper conduction band and higher electron mobility, and can efficiently serve as an electron transport layer to facilitate charge extraction and transfer. Herein, an optimized low‐temperature solution‐processed SnO 2 electron transport layer is achieved by doping polyethylenimine polyelectrolyte into SnO 2 for the first time in the PSCs. It is found that the performance of all aspects of the doped SnO 2 film is improved over that of the pristine SnO 2 film. The better energy level alignment, larger built‐in field, enhanced electron transfer/extraction, and reduced charge recombination all contribute to the improved device performance. Finally, a PSC with a power conversion efficiency of 20.61% is successfully prepared under low temperature below 150 °C. Moreover, the stability of the doped SnO 2 ‐based device is also greatly improved.