Synthesis and optical characterization of lead-free phenylenediammonium bismuth halide perovskites: a long charge carrier lifetime in phenylenediammonium bismuth iodide

Toxicity and regulatory concerns over the use of (CH3NH3)PbI3 in photovoltaic devices have resulted in significant interest in lead-free, organic-inorganic metal halides with excellent light absorbing properties and stability. Here we report the synthesis of three new lead-free bismuth halides which accommodate the symmetric conjugated p-phenylenediammonium cation (PPD = (H3NC6H4NH3)2+) in the structures. These are (PPD)BiI5, (PPD)[BiBr4]2·2H2O (2) and (PPD)2BiCl7·H2O. We also synthesized β-(PPD)2Bi2I10. The band gap of the iodide, β (PPD)2Bi2I10 (1.83 eV) is lower than that of the bromide, (PPD)[BiBr4]2·2H2O ( 2.64 eV) and chloride, (PPD)2BiCl7·H2O (2.93 eV). Photophysical studies show that β (PPD)2Bi2I10 has the longest average charge carrier lifetime (>1 us) of the materials studied here, of the same order of magnitude as that of (CH3NH3)PbI3 and has a low band gap. This suggests that β (PPD)2Bi2I10 may be a promising candidate for use in lead-free photovoltaic devices.