Two-Step Processed Efficient Potassium and Cesium-Alloyed Quaternary Cations Perovskite Solar Cells

Abstract Organic-inorganic hybrid perovskite solar cells (PSCs) are continuously attracting much attention due to the poential applications in low-cost and flexible solar energy system. In this work, potassium (K+) and cesium (Cs+) were added into the perovskite (FAMA)Pb(IBr)3 (FA = CH(NH2)2+, MA = CH3NH3+) to prepare the high-quality quadruple-cation (KCsMAFA) perovskite film and PSCs via two-step solution process. The optoelectronic properties and stability of FAMA, CsFAMA and KCsFAMA perovskite film and PSC devices were systematically studied and analyzed. The power conversion efficiency (PCE) of champion KCsFAMA device reached 19.70%, and the steady output PCE was 19.40% with a simple device structure of ITO/SnO2/Perovskite/Spiro-OMeTAD/Ag. In addition, the stability of PSCs with quadruple-cation KCsMAFA was significantly improved as compared to the control ones. With the storage in air for 20 days (humidity ∼35%), the PCEs of PSCs without encapsulation could maintain 77% of the initial values, while the PCEs of PSCs with MAFA and CsMAFA only maintained 39% and 56% of their initial values, respectively. The improved efficiency and stability in PSCs with both K+ and Cs + were attributed to significant improvement in the film quality with large and dense grains, which could reduce grain boundaries and moisture immersion. Meanwhile, the incorporation of K+ and Cs+ could enhance the charge transfer resistance and suppress the charge recombination effectively, supporting in the improvement in the performance of PSCs.