A-Site Mixing to Adjust the Photovoltaic Performance of a Double-Cation Perovskite: It Is Not Always the Simple Way.

Considerable progress has been made in improving the performance of optoelectronic devices based on hybrid organic-inorganic perovskites of the form ABX3. However, the influences of A-site doping on the structure and dynamics of the inorganic perovskite crystal lattice and, in turn, on the optoelectronic performance of the resulting devices remain poorly understood at an atomic level. This work addresses this issue by combining the results of several experimental characterization methods for three-dimensional MA1-xDMAxPbBr3 perovskite single crystals (MA, methylammonium; DMA, dimethylammonium). The results reveal a two-stage change in lattice with an increase in DMA content, which has completely opposite effects on the optoelectronic performance of the double-cation perovskite. At low DMA concentrations, fast reorientation of incorporated DMA cations strengthens the interaction between MA cations and the lattice without significant lattice distortion, which could suppress lattice fluctuation and thus improve the photovoltaic performance. At high DMA concentrations, the lattice get a severe distortion, leading to poorer photovoltaic performance.