Stable high conversion efficiency of Quasi-2D perovskite solar cells via potassium iodide as additive

Although two-dimensional (2D) perovskite is more stable than three-dimensional (3D) perovskite, its poor film quality and low photoelectric conversion efficiency are still the focuses of researchers. In this article, we introduce a simple and effective method to modify the quasi-2D (BA)2(MA)3Pb4I13 perovskite solar cells by introducing potassium iodide as an additive. We found that the introducing K ion made perovskite film more compact, reduced the number of grain boundaries and regulated the band alignment. Besides, the incorporation of K+ reduced the nonradiative recombination and hysteresis effect of the device. As a result, the power conversion efficiency (PCE) of solar cells increased from initial 13.91% to 16.82% under optimized concentration of 16% (mole ratio compared to N-butyl ammonium iodide BAI). What is more, the device with K+ modification showed excellent environmental stability, which could maintain 95% of their original efficiency after 720 h under ambient air condition, whereas the pristine devices without K+ only keep 53% of their initial efficiency and the thermal stability has also been improved. This result provides a simple and promising method through additive engineering to achieve high PCE and stable quasi-2D perovskite solar cells.