Efficient and Hole-Transporting-Layer-Free CsPbI ₂ Br Planar Heterojunction Perovskite Solar Cells through Rubidium Passivation

Recently, inorganic perovskite CsPbI ₂ Br has gained much attention for photovoltaic applications owing to its excellent thermal stability. However, low device performance and high open-voltage loss, which are the result of its intrinsic trap states, are hindering its progress. Herein, planar CsPbI ₂ Br solar cells with enhanced performance and stability were demonstrated by incorporating rubidium (Rb) cations. The Rb-doped CsPbI ₂ Br film exhibited excellent crystallinity, pinhole-free surface morphology, and enhanced optical absorbance. By using low-cost carbon electrodes to replace the organic hole-transportation layer and metal electrode, an excellent efficiency of 12 % was achieved with a stabilized efficiency of over 11 % owing to the suppressed trap states and recombination in the CsPbI ₂ Br film. Additionally, the annealing temperature for the Rb-doped CsPbI ₂ Br film could be as low as 150 °C with a comparable high efficiency over 11 %, which is one of the best efficiencies reported for hole-transporting-layer-free all-inorganic perovskite solar cells. These results could provide new opportunities for high-performance and stable inorganic CsPbI ₂ Br solar cells by employing A-site cation substitution.