CH3NH2BiI3 Perovskites: A New Route to Efficient Lead-Free Solar Cells

CH3NH3PbI3-based perovskite solar cells have achieved great success in the past several years. However, their further large scale application is hindered by the toxicity of the Pb. Here, the existence of a stable perovskite structure with close to optimum optical properties for solar cells with Pb replaced by Bi was shown by theoretical modeling. It was found that the cubic perovskite BiI3 framework is maintained only when the polar organic group of CH3NH3+ is dissociated into neutral CH3NH2 molecule and hydrogen. The band gap of the neutral molecular filled CH3NH2BiI3 perovskite structure gives a value of 1.61 eV, which matches closely the solar spectrum with a maximum possible efficiency of 28.5% close to the Shockley–Queisser limit of 33% for a single stage cell, offering a new and promising lead-free route for perovskite solar cells.