Cesium lead iodide solar cells controlled by annealing temperature

Abstract

An inorganic lead halide perovskite film, CsPbI₃, used as an absorber in perovskite solar cells (PSCs) was optimized by controlling the annealing temperature and the layer thickness. The CsPbI₃ layer was synthesized by one-step coating of CsI mixed with PbI₂ and a HI additive in N,N-dimethylformamide. The annealing temperature of the CsPbI₃ film was varied from 80 to 120 °C for different durations and the thickness was controlled by changing the spin-coating rpm. After annealing the CsPbI₃ layer at 100 °C under dark conditions for 10 min, a black phase of CsPbI₃ was formed and the band gap was 1.69 eV. Most of the yellow spots disappeared, the surface coverage was almost 100%, and the rms roughness was minimized to 3.03 nm after annealing at 100 °C. The power conversion efficiency (PCE) of the CsPbI₃ based PSC annealed at 100 °C was 4.88%. This high PCE value is attributed to the low yellow phase ratio, high surface coverage, low rms roughness, lower charge transport resistance, and lower charge accumulation. The loss ratio of the PCE of the CH₃NH₃PbI_xCl_3−x and CsPbI₃ based PSCs after keeping in air was 47 and 26%, respectively, indicating that the stability of the CsPbI₃ based PSC is better than that of the CH₃NH₃PbI_xCl_3−x based PSC. From these results, it is evident that CsPbI₃ is a potential candidate for solar cell applications.