Enhancement of thermal stability for perovskite solar cells through cesium doping

Organic-inorganic hybrid perovskite solar cells are found to be sensitive to moisture, oxygen, UV light, light soaking, heat, electric field, etc. Among all these factors, thermal stability is one of the most challenging concerns affecting PSCs stability, since it is hard to avoid a temperature increase for solar cells during operation. In this work, we systematically studied the thermal stability of Cs(x)MA(1-x)PbI(3) film and solar cells. The introduction of Cs into the precursor solution would inevitably accelerate the film deposition rate, resulting in decreased grain size and more Cs atoms in the film than in the precursors. The study on thermal stability illustrated that perovskite degradation was highly related to the amount of oxygen in the air. A small amount of Cs doping (x = 0.09) was beneficial for better thermal stability. In addition, Cs doping also enhanced the device performance. The improvement of short-circuit currents came from the increased film thickness, which was due to the faster deposition rate for Cs doped samples. Besides, Cs doping was vital to suppress the trap states in the film since the trap states were related to halide deficiency during thermal annealing. At last, the final performance of Cs(0.09)MA(0.91)PbI(3) reached 18.1%, with a J(SC) of 22.57 mA cm(-2), V-OC of 1.06 V, FF of 0.76.