Hybrid perovskites for photovoltaics: Insights from first principles

The methylammonium lead iodide perovskites at the core of recently proposed solar cells with exceptionally large quantum conversion efficiency are studied by first-principles methods. Large absorption coefficients (0. 03--0. 04 nm^-1 for wavelength 500 nm) and small effective masses suited for both n-type and p-type transport are obtained as a consequence of their peculiar structural and electronic characteristics. In particular, the presence of a direct gap between highly dispersed Pb (6s) -I (5p) valence bands and Pb (6p) conduction bands is the key ingredient at the basis of their excellent performance in photovoltaic applications.