The Cesium doping using the nonstoichiometric precursor for improved CH₃NH₃PbI₃ perovskite films and solar cells in ambient air

Organic-inorganic hybrid perovskite solar cells have shown great prospect as a low-cost and high efficiency photovoltaic technology. The quality of the perovskite absorber layer is most critical to the performance of the device, and the stability remains one of the challenging issues. In this paper, the Cesium (Cs) doping perovskite film was prepared from nonstoichiometric precursor solution in ambient and humidity-controlled conditions. The results showed that the crystallinity, uniformity, absorption, Photo-luminescence intensity and the thermal stability of these films can be effectively improved compared with the films fabricated from stoichiometric one, which is attributed to the combined effect of the Cs doping and excess methylammonium cations passivation. Finally, the highest efficiency of the perovskite solar cells fabricated from nonstoichiometric solution reached to 14.1%, which is 12.8% higher than that of the control device from stoichiometric solution (12.5%). Furthermore, the device displayed the high stability and efficiency degradation of only 2% occurring over a period of 5 weeks in ambient air without encapsulation. This reported work provides a pathway for further improving the performance of perovskite solar cells with higher stability.