Self-stability of un-encapsulated polycrystalline MAPbI3 solar cells via the formation of chemical bonds between C60 molecules and MA cations

The day-dependent photovoltaic performance of P3CT-Na based CH3NH3PbI3 (MAPbI3) solar cells can be improved by adding small molecules (urea, PCBM and C60) into the MAPbI3 crystal thin films to passivate the defects at the grain boundaries. The experimental results show that the passivation mechanism of the different additives does not only depend on the type of additives but also be related to the chemical interaction between additives and MAPbI3 crystals. Atomic-force microscopic images, day-dependent photoluminescence (PL) spectra, and temperature-dependent PL shows that the chemical bonds between C60 molecules and MA cations can be formed and thereby stabilizing the MAPbI3 crystal thin films. In other words, the stable and high-efficiency P3CT-Na based MAPbI3 solar cells can be realized when the surface defects of MAPbI3 crystal grains are passivated with the MA-C60-MA cations. Our results provide a way to increase the device stability of the solution-processed polycrystalline MAPbI3 thin film based solar cells.