Computational study of lead-free (CH3NH3)2AuIAuIIIX6 (X = Cl, Br, I) for solar cell applications

Herein, lead-free MA2AuIAuIIIX6 (MA = CH3NH3, X = Cl, Br, I) is recommended as a potential candidate for perovskite solar cells via the first-principles calculations. Structural analysis shows that lattice contraction and octahedral distortion occur simultaneously since the cesium cations at the A-site are substituted by larger organic methylammonium cations. The good thermodynamic and thermal stability is confirmed according to our theoretical predictions. The MA2AuIAuIIIX6 perovskites are predicted as direct-gap semiconductors with an optimal value of 0.86–1.35 eV. The structural changes involving lattice contraction and octahedral distortion can offer an explanation for the lower band gap of MA2AuIAuIIIX6 in comparison with the case of Cs-based analogue. Furthermore, these perovskites not only show superior visible-light absorption coefficients (>105 cm−1), but also possess high conversion efficiencies, especially for MA2AuIAuIIIX6 (X = Cl, Br), whose efficiency can reach 26−27% in the film thickness of 1.0 μm. These excellent optoelectronic properties render the MA2AuIAuIIIX6 perovskites promising high-performance photovoltaic materials.