Enhanced Stability of Ge-Doped CsPb(I1-xBrx)3 Perovskite Solar Cells

All-inorganic CsPb(I1-xBrx)3 perovskite solar cells (PSCs) have increasingly broken record power conversion efficiency (PCE), however the poor stability in humid environment is still a serious bottleneck. To suppress the humidity-caused rapid transformation from black phase to yellow phase, germanium (Ge) doping is introduced to improve the tolerance factor of CsPb1-xGexI2.85Br0.15 and its photoelectric performance. A combined investigation of the structural and optical properties reveals a successful substitution of lead (Pb) with Ge in the films as well as a champion PCE of 19.70% for the 1% Ge doped PSC. More significantly, the Ge doped device retained 91.5% of its initial efficiency after being stored in air for 500 hours without any encapsulation process, in contrast to the 83.7% for the undoped counterpart.