Polyvinylpyrrolidone/polyvinyl alcohol blends modification on light absorbing layer to improve the efficiency and stability of perovskite solar cells

The high-power conversion efficiency (PCE) and long-term environmental stability are two critical factors for the development of organic-inorganic hybrid perovskite solar cells (PSCs). Herein, blends of polyvinylpyrrolidone (PVP) and polyvinyl alcohol (PVA) have been added to improve the quality of perovskite film, stabilize perovskite crystal structure, and enhance the efficiency and air stability of PSCs. The device modified by 1.5 wt%PVP/ 0.5 wt%PVA shows a 28.3% increasement of PCE compared to that of the pristine one. Most importantly, the unencapsulated device retains over 82.2% of its initial efficiency even after 30 days in an atmospheric environment with 70% relative humidity. Furthermore, the effect mechanisms of PVP/PVA blends on the properties of Cs0.2FA0.3MA0.5Pb(I0.85Br0.15)3 film and the performance of corresponding solar cell were clarified. For one thing, the interactions between O atoms of C--O in PVP and the incomplete coordinated Pb in Cs0.2FA0.3MA0.5Pb (I0.85Br0.15)3 passivate the defects in perovskite. For another thing, the hydrogen bonds between O atoms of OH in PVA, and H atoms of MA (CH3NH3+) and FA (CH(NH2)2+) in Cs0.2FA0.3MA0.5Pb(I0.85Br0.15)3 stabilize the perovskite structure. Such synergistic effect between PVP/PVA blends and Cs0.2FA0.3MA0.5Pb(I0.85Br0.15)3 perovskite effectively optimized the quality of perovskite film and stabilized perovskite film, ultimately improving the device performance. Our study provides a useful way to simultaneously improve the efficiency and stability of lead halide PSCs, and supplies a profitable reference for their commercialization.