Compositional study of mixed halide perovskite films CH3NH3Pb(I1-Br )3 and CH3NH3Pb(I1-Cl )3 prepared by close space sublimation

The preparation and characterization of homogeneous and crystalline films of the perovskites CH3NH3Pb(I1-xBrx)3 and CH3NH3Pb(I1-xClx)3 obtained by the close space sublimation method are reported. Perovskites with a mixture of halides were prepared by the sublimation of the methylamine halide CH3NH3Br or CH3NH3Cl over predeposited lead iodide films at different sublimation times to modify the I:Br or I:Cl ratio. The perovskite films CH3NH3Pb(I1-xBrx)3 showed a bandgap shift. For CH3NH3Pb(I1-xClx)3 films with sublimation times of 2.5−40 min, no changes were observed; however, for longer times, the absorption spectrum became similar to that of the CH3NH3PbCl3 material. In this study, the mixed halide perovskites CH3NH3Pb(I1-xBrx)3 and CH3NH3Pb(I1-xClx)3 were prepared with just two precursors, instead of the common approaches that use PbI2, PbBr2, MAI and MABr, as well as PbI2, PbCl2, MAI and MACl. Perovskite layers were applied for the fabrication of solar cell devices, and efficiencies of 9.9 % and 10.2 % were achieved for CH3NH3Pb(I1-xBrx)3 and CH3NH3Pb(I1-xClx)3, respectively. In addition, perovskite LEDs were also prepared. While the well-known green emission at 533 nm was observed for CH3NH3Pb(I1-xBrx)3, for the CH3NH3Pb(I1-xClx)3 based-devices, a broad emission spectrum similar to a warm white emission was obtained. Therefore, a new approach through the sublimation method is reported to fabricate solar cells and LEDs where the main parameter to regard is the sublimation time.