Effect of Rubidium Incorporation on the Structural, Electrical, and Photovoltaic Properties of Methylammonium Lead Iodide-Based Perovskite Solar Cells

We report the electrical properties of rubidium-incorporated methylammonium lead iodide ((Rb_xMA_1-x)PbI₃) films and the photovoltaic performance of (Rb_xMA_1-x)PbI₃ film-based p-i-n-type perovskite solar cells (PSCs). The incorporation of a small amount of Rb⁺ (x = 0.05) increases both the open circuit voltage (V_oc) and the short circuit photocurrent density (J_sc) of the PSCs, leading to an improved power conversion efficiency (PCE). However, a high fraction of Rb⁺ incorporation (x = 0.1 and 0.2) decreases the J_sc and thus the PCE, which is attributed to the phase segregation of the single tetragonal perovskite phase to a MA-rich tetragonal perovskite phase and a RbPbI₃ orthorhombic phase at high Rb fractions. Conductive atomic force microscopic and admittance spectroscopic analyses reveal that the single-phase (Rb_0.05MA_0.95)PbI₃ film has a high electrical conductivity because of a reduced deep-level trap density. We also found that Rb substitution enhances the diode characteristics of the PSC, as evidenced by the reduced reverse saturation current (J₀). The optimized (Rb_xMA_1-x)PbI₃ PSCs exhibited a PCE of 18.8% with negligible hysteresis in the photocurrent-voltage curve. The results from this work enhance the understanding of the effect of Rb incorporation into organic-inorganic hybrid halide perovskites and enable the exploration of Rb-incorporated mixed perovskites for various applications, such as solar cells, photodetectors, and light-emitting diodes.