2D hybrid organic-inorganic lead halide perovskites (HOIPs) feature remarkable chemical stability and promising optoelectronic properties for solar energy conversion but suffer from lead-toxicity. Isoelectronic cations to PbII such as BiIII or SbIII are attractive candidates for exploring Pb-free HOIPs. However, to meet valence requirements, either dual metals with an average oxidation state of 2+ must be used, or a substantial metal-vacancies must be stabilized when using only a trivalent metal such as BiIII. Pb-free iodide based 2D HOIPs with prospectively lower bandgaps constitute an essential target for hybrid semiconductors but have so far been thwarted due to either intrinsic instability or formation of competing non-perovskite phases. Our goal is to exploit the unique templating influence of specially designed bifunctionalized oligothiophene cations— via strong aromatic interactions and structural rigidity—to stabilize lead-free 2D HOIPs that are otherwise unstable with traditional organic spacer cations.
