Rietveld Refinement of the Crystal Structure of Perovskite Solar Cells Using CH3NH3PbI3 and Other Compounds

摘要

The crystal structures of perovskite thin films including CH3NH3PbI3, CH_3NH_3Pb_(1-x)Sb_xI_3, and CH_3NH_3PbI_3-_yCl_y in the solar cell configuration were studied by using Rietveld refinement. For the CH_3NH_3PbI_3 and CH_3NH_3Pb_(1-x)-x_1Sb_(xI3) samples, satisfactory agreement with the measured profiles was obtained with a weighted profile R-factor (Rwp) of as low as 3%. It was shown that the site occupancy of methylammonium (MA) was decreased in the antimonized cell due to the compensation effect of an increased positive charge brought about by replacing Pb~(2+) with Sb~(3+). Photovoltaic measurements showed that the power conversion efficiency was enhanced by adding a small amount of Sb to the CH_3NH_3PbI_3 cell, but it was monotonically decreased as the mole fraction of Sb exceeded 0.03. This variation of the conversion efficiency was considered as a result of suppressed crystallization ofPbI_2 and carrier recombination via MA vacancies in the antimonized cells. In the case of CH3NH3PbI_(2.88)Cl_(0.12) sample, the agreement with the measured profile with an R_(wp) of as high as 7% suggested the co-existence of cubic and tetragonal phases in the chlorinated cell.