Ca(CF3SO3)2 all-in-one modification on CsPbI3 all-inorganic perovskite solar cells for improved performance and stability

Due to the low tolerance factor, the black-phase CsPbI3 could easily transform into the photovoltaic-inactive yellow phase under the pressure of moisture, restricting the performance and stability of corresponding solar cells. Here, Ca(CF3SO3)2 is introduced into CsPbI3 to solve this problem. The Ca2+ cations could interact with I− ions to inhibit ion migration and prevent the collapse of the perovskite structure, while the CF3SO3− anions anchoring on the crystal surface could provide hydrophobicity. Ca(CF3SO3)2 introduction, thus, increases the intrinsic and extrinsic stability of black-phase CsPbI3 simultaneously. The interaction between Ca(CF3SO3)2 and perovskite precursors retards the crystallization process and facilitates the growth of high-quality films with reduced non-radiative recombination. Moreover, the CF3SO3− anions on the surface induce p-type doping and modify the energy level alignment with the hole transport layer. Benefiting from the Ca(CF3SO3)2 introduction, the CsPbI3 all-inorganic perovskite solar cells exhibit improved power conversion efficiency (PCE) from 14.76% to 16.50%. In addition, the unencapsulated device with Ca(CF3SO3)2 retains 81% of its original PCE after storage in air for 500 h, outperforming that of the control device (65%).