Insight into lead-free organic-inorganic hybrid perovskites for photovoltaics and optoelectronics: A first-principles study

Semiconducting lead (Pb) free organic-inorganic hybrid perovskites have become more attractive for possible applications in solar cells and other optoelectronic devices. In this study, a first-principles density functional theory (DFT) calculations have been carried out to explore the structural, electronic, optical and mechanical properties of Pb-free organic-inorganic hybrid perovskites MABX3 (MA = CH3NH3, B = Sn, Ge; X = I, Br, Cl) and the results are compared with the Pb-containing perovskites MAPbX3 (X = I, Br, Cl). High absorption, low reflectivity and high optical conductivity have been observed in our simulations. These compounds are found to be direct band gap semiconductors suitable for solar cells and other optoelectronic devices. Our calculation indicates that tin (Sn) has superior properties alternative to Pb as the Sn containing compounds have excellent electronic, optical and mechanical properties. MASnI3 is found to be one of the best Pb-free materials embracing these properties. For example, the unique mechanical property of MASnI3 makes the compound flexible and easy to be fabricated into thin films. We believe these results will benefit the development of Pb-free hybrid solar cells as well as other optoelectronic devices