CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3−x</sub>Cl<sub>x</sub> films with coverage approaching 100% and with highly oriented crystal domains for reproducible and efficient planar heterojunction perovskite solar cells
Depositing pinhole-free perovskite films is of vital importance for achieving high performance perovskite solar cells, especially in a planar heterojunction device. Here, perovskite films with coverage approaching 100% and with highly oriented crystal domains were obtained by carefully controlling the annealing temperature and duration. Perovskite solar cells with an average efficiency of 12% and a maximum efficiency of 15.17% were achieved in a planar heterojunction structure. Comprehensive characterization and analysis showed that appropriate annealing temperature and duration allowed the perovskite crystals to grow slowly, resulting in highly oriented crystal domains without any internal voids or pinholes. The anisotropic transport properties of perovskite crystals ensure efficient electron and hole transport to their corresponding electrodes.