Highly efficient flexible solar cells based on a room-temperature processed inorganic perovskite

All-inorganic perovskite cesium lead triiodine (CsPbI3) is emerging as a promising thermally stable light absorber in flexible optoelectronic devices. However, the photoactive alpha-CsPbI3 only exists at a temperature higher than 310 degrees C and rapidly degrades to the undesired delta-CsPbI3 at room temperature. Here, a vacuum-assisted drying process is first developed to fabricate all-inorganic perovskite thin films at room temperature. The film morphology and photoelectric properties as well as the long-time stability are significantly improved compared to those of the reference film fabricated with annealing process. The flexible solar cells based on such room temperature processed films demonstrate a high power conversion efficiency of 11.47% with a small hysteresis. Moreover, the champion flexible cell also exhibits high air-stability and excellent flexibility. These results offer a new pathway for developing high-performance and cost-effective flexible optoelectronic devices.