A step towards environmental benign Mg/Pb based binary metal mixed halide perovskite material

Abstract

Today's the best performing perovskite solar cells utilise Pb2+ as a major bivalent cation source, however, the presence of toxic Pb is major issue that put its commercialization in dire straits. In this report, we unveiled the chemical synthesis and characterisation of Mg/Pb binary metal mixed halide perovskite with chemical formula CH3NH3PbxMg1−xI3−yCly using MgCl2 as a compositional gradient with nominal value of x from 0.1 to 0.9. The FESEM images of compositions corresponding to higher proportion of Cl- (or MgCl2) demonstrate improved particle (or grain) size of ∼ 8–12 μm. There is a close resemblance of stoichiometric ratio of Pb:Mg obtained from EDX analysis with that of incorporated stoichiometric ratio of Pb:Mg. Further, Mg and Cl incorporation is strengthened by the characteristic spectral peak for core level electron of Mg(2p) and Cl(2p) other than Pb(4f) and I(3d) in the XPS survey spectrum of composition x = 0.5. These binary Mg/Pb Perovskite with bandgap in the range 1.57–1.59 eV behave as comparatively less toxic potential candidate for the single junction module. The IR studies at room temperature show observable shift in peak positions on comparing two extreme compositions i.e., x = 0.1 and x = 1.0. It is noticeable that both standard CH3NH3PbI3 and binary Mg/Pb Perovskite with nominal value x = 0.7 have comparable thermal stability, however, the composition x = 0.1 have lower thermal stability than x = 0.7. The carrier lifetimes measurements by Microwave Detected Photoconductivity (MDP) showed an improvement of lifetime to 142 μs for nominal value x = 0.9 compared to 76 μs in case of MAPbI3 film. Correspondingly we see a 160 mV improvement in open-circuit voltage (VOC) in the solar cells fabricated with nominal value x = 0.9 (VOC = 1.07 V) as compared to standard MAPbI3 cells (VOC = 0.90 V). The champion cell with nominal value x = 0.9 shows PCE of 14.2% where as the best PCE of MAPbI3 cell is 14.50% under a reverse scan.