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

Abstract

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 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 μs) 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.