Control over Self‐Doping in High Band Gap Perovskite Films

It is reported how differences in the composition of high bandgap Pb bromide‐based perovskites affect their carrier diffusion length and junction type. Pb‐based, APbX₃, halide perovskite (HaP) films and devices are studied, where A can be a mixture of formamidinium, methylammonium (MA), and Cs, and X a mixture of Br and Cl, using a combination of dark‐ and photoconductivity and steady‐state photocarrier grating. The results show the cation and anion compositions affect both majority and minority carrier diffusion lengths. In particular, using electron beam‐induced current measurements, FTO\dTiO₂mp‐TiO₂HaP\PTAA (poly‐triarylamine)\Au devices are studied. The results enable identifying junction and built‐in voltage formation and track position and size of the space charge region width with changes in the HaP composition. As far as it is known, it is found for the first time that a mixed‐cation HaP forms a junction that has characteristics of a p‐i‐n one, with relatively long and comparable carrier diffusion lengths, while the single cation‐based bromide HaPs form clear p‐n junctions at the interface with the TiO₂ pure CsPbBr₃ and MAPbBr₃(Cl)] or a buried one (MAPbBr₃) and shorter diffusion lengths. These differences are attributed to lower carrier density in MAPbBr₃, and especially in the mixed cation HaP, which is comparable to iodide‐based HaP films.