Enormous research efforts are currently devoted to the discovery of ‘perovskite-inspired materials’, aiming to replicate the astonishing optoelectronic performance of lead-halide perovskites (LHPs). Recently, chalco halides of group IV/V elements have attracted attention due to the stability provided by stronger metal-chalcogen bonds, alongside compositional flexibility and ns2 cations — a performance-defining feature of LHPs. A detailed theoretical description of their atomistic properties and future performance potential is lacking, however. Following the experimental report of stable, solution-grown tin-antimony sulfoiodide (Sn2SbS2I3) solar cells, with power conversion efficiencies above 4%, we comprehensively characterise the structural and electronic properties of this emerging material. To ensure an accurate model for both the phase energetics and electronic structure, we employ the Random Phase Approximation (RPA) to the correlation energy for the calculation of relative formation energies, while Hybrid Density Functional Theory including spin-orbit coupling (HSE06+SOC) is used for electronic and optical calculations. We find that the experimentally-reported centrosymmetric Cmcm crystal structure represents an average over multiple polar Cmc21 configurations. This dynamic crystal structure and hidden ferroelectric behaviour could benefit photovoltaic performance. Using state-of-the-art ab initio methods, we assess the efficiency limits of this material, finding maximal solar-conversion efficiencies ηmax &gt; 30% with film thicknesses t &gt; 0.5 μm, at the radiative limit, alongside several defect-tolerant properties. These results shine the spotlight on the largely-unexplored class of A2BCh2X3 mixed-metal chalco halides as candidates for solution-processed ferroelectric and optoelectronic devices, with the substitutional flexibility of both cation and anion sites permitting, for example, bandgap tuning, polarisation tuning and engineered band alignments.

Hidden spontaneous polarisation in the ns2-cation Sn2SbS2I3 chalcohalide photovoltaic absorber

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.