CsBr interface modification to improve the performance of perovskite solar cells prepared in ambient air

For future mass production, it is the best choice to fabricate highly efficient and stable perovskite solar cells (PSCs) in the ambient air. Interface modification is widely reported as an effective method for boosting the power conversion efficiency (PCE) and stability of PSCs. In our manuscript, CsBr as the interface modification material was introduced into the mesoporous TiO2 (mp-TiO2) via two ways: doping into the mp-TiO2 layer and inserting between the mp-TiO2 and perovskite films. It was found that CsBr interface modification, especially by doping into the mp-TiO2 layer, can passivate the trap states originated from VO in mp-TiO2 leading to enhanced carrier transport properties, meliorate surface property of mp-TiO2 resulting in high-quality perovskite films, improve the carrier extraction and decrease the trap recombination in the interface. High-quality perovskite films, with increased grain size, reduced grain boundaries and pinholes, were obtained after CsBr modification, and further applied for the PSCs. The whole preparation process of the PSCs was finished in ambient air. The champion device with CsBr doped into the mp-TiO2 layer yielded a highest PCE of 17.33%, while the pristine device showed a PCE of 14.95%. Furthermore, the champion PSC with CsBr doped into the mp-TiO2 layer exhibited a much better stability, which could maintain over 80% of the original PCE after 1000h storing in ambient air without any encapsulation. This work presents an approach to develop air-processed efficient and stable PSCs by interface modification for future mass production.