Effects of CH3NH3PbI3 Perovskite Films Crystal Structure on Solar Cell Performances

The phase transition of MAPbI3 during the annealing process has been extensively reported, but there is a lack of research on the preformation of resulting perovskite solar cells (PSCs). Here, we systematically investigated the impact of annealing temperature on the crystal structure of MAPbI3. Our findings reveal that an optimal annealing temperature of 100°C yields high crystallinity and a mixture of tetragonal and cubic phases. Deviating from this temperature range results in incomplete conversion to perovskite material at lower temperatures or formation of only cubic crystal structure above 100°C, leading to degradation at higher temperatures. Theoretical calculations also indicate that the conduction band energy level for the cubic phase is approximately 154 meV lower than that for the tetragonal phase, creating an electron extraction barrier between perovskite and TiO2. Solar cells fabricated with mixed-phase films annealed at 100°C exhibit superior performance with a conversion efficiency of 22.01%, attributed to both energetically favourable crystal structure and excellent crystallinity.