Chlorine doping for black γ-CsPbI3 solar cells with stabilized efficiency beyond 16%

Although the solar cells based on the α-CsPbI3 presents very impressive power conversion efficiency, it suffers from insufficient crystalline structure stability even in ambient condition. Herein, the black orthorhombic γ phase based CsPbI3 is successfully fabricated with its performance further optimized by doping chlorine ions. It is found that the chlorine incorporation improves crystallization dynamics for favorable surface morphology and crystalline orientation. In particular by doping 3 mol% chlorine into the γ-CsPbI3 film, its trap density is minimized with enhanced black phase stability and much improved thin film characteristics, including conductivities, electron and hole mobilities. Consequently, the solar cell efficiency is increased to as high as 16.07%. More importantly, the PCE of the optimized device shows only 0.45% degradation after continuous light soaking for 200 h. It retains as much as 94% of its initial PCE even after being exposed in air (relative humidity of 20–30% at 25 °C) for 60 days.