Unraveling current hysteresis effects in regular-type C₆₀-CH₃NH₃PbI₃ heterojunction solar cells

Comprehensive studies were carried out to understand the origin of the current hysteresis effects in highly efficient C₆₀-CH₃NH₃PbI₃(MAPbI₃) heterojunction solar cells, using atomic-force microscopy, transmittance spectra, photoluminescence spectra, X-ray diffraction patterns and a femtosecond time-resolved pump-probe technique. The power conversion efficiency (PCE) of C₆₀-MAPbI₃ solar cells can be increased to 18.23% by eliminating the point (lattice) defects in the MAPbI₃ thin film which is fabricated by using the one-step spin-coating method with toluene washing treatment. The experimental results show that the point defects and surface defects of the MAPbI₃ thin films can be minimized by varying the dropping time of the washing solvent. The point defects (surface defects) can be reduced with an (a) increase (decrease) in the dropping time, resulting in an optimized dropping time for obtaining the defect-minimized MAPbI₃ thin film deposited on top of the C₆₀ thin film. Consequently, the formation of the defect-minimized MAPbI₃ thin film allows for high-efficiency MAPbI₃ solar cells.