CsPbI₃ Perovskite Quantum Dot Solar Cells with Both High Efficiency and Phase Stability Enabled by Br Doping

All-inorganic CsPbI3 perovskite quantum dots (QDs) have attracted great attention since emerging as a new class of materials with superior light-harvesting properties and enhanced thermal stability compared to organic–inorganic hybrid perovskites. However, poor phase stability remains a bottleneck for practical applications. In the present work, CsPb(I1–xBrx)3 perovskite QDs are synthesized by Br doping to increase the tolerance factor for the improvement of phase stability, and the balance between the stability of solar cells and the power conversion efficiency (PCE) is considered by adjusting the Br doping content. It is found that the phase stability of CsPb(I1–xBrx)3 QDs is much improved, while their band gap increases from 1.77 to 1.89 eV when the Br doping content increases from 0 to 30%. CsPbI2.4Br0.6 QD-based perovskite solar cells (PSCs) achieve a proper balance between high PCE and stability; the PCE is 12.31%, approaching that of the CsPbI3-based PSCs (14.13%), and may retain 87% of the initial efficiency after 15 days of storage in ambient air.