Relationship between Lattice Strain and Efficiency for Sn-Perovskite Solar Cells

In the composition of Q0.1(FA0.75MA0.25)0.9SnI₃, Q is replaced with Na⁺, K⁺, Cs⁺, ethylammonium⁺ (EA⁺), and butylammonium⁺ (BA⁺), respectively, and the relationship between actually measured lattice strain and photovoltaic performances is discussed. The lattice strain evaluated by the Williamson-hall plot of X-ray diffraction data decreased as the tolerance factor was close to one. The efficiency of the Sn-perovskite solar cell was enhanced as the lattice strain decreased. Among them, EA0.1(FA0.75MA0.25)0.9SnI₃ having lowest lattice strain gave the best result of 5.41%. Because the carrier mobility increased with a decrease in the lattice strain, these lattice strains would disturb carrier mobility and decrease the solar cell efficiency. Finally, the results that the efficiency of the SnGe-perovskite solar cells was gradually enhanced from 6.42 to 7.60% during storage, was explained by the lattice strain relaxation during the storage.