Improved efficiency and air stability of two-dimensional p-i-n inverted perovskite solar cells by Cs doping

Two-dimensional perovskite solar cells (2-D PSCs) have attracted much research attention in recent years because they are more stable in a regular environment than three-dimensional (3-D) ones are. In this study, we doped Cs into 2D perovskite (BA₂(MA)₂Pb₃I₁₀) films as the absorbing layers of the 2-D p-i-n inverted PSCs to investigate the influence of the Cs doping concentration on the properties of the 2-D perovskite films and the fabricated solar cells. Cs doping clearly improves the power conversion efficiency (PCE) and air stability of the PSCs. Doping perovskite with 10% Cs (the best doping concentration in this study) can increase the PSC efficiency from 7.98% to 10.11%. Scanning electron microscopy indicates the improved surface quality and crystallinity by Cs doping. However, excess Cs doping degrades the PCE of the PSCs. Furthermore, 10% Cs doped PSCs show air stability superior to that of undoped ones in unpackaged humidity environments. After exposure to 55% relative humidity (RH) in 19 °C air for 300 h, the PCE of the PSC decreased by only 39%, in contrast to 84% for the undoped PSC.