Ag/In lead-free double perovskites

Lead-free Cs2AgInCl6 and Cs2AgInBr6 double perovskites are studied by a combination of advanced ab-initio calculations and photoluminescence experiments. We show that they are insulators with direct band gaps of 2.53 and 1.17 eV, respectively; most importantly, they are characterized by unusually low absorption rates in a similar to 1 eV wide energy region above the band gap, caused by rather peculiar electronic properties. Consequently, this low absorption conveys very long recombination lifetimes, up to milliseconds at low temperature. Our theoretical analysis suggests that such materials can achieve a good compromise between photoconversion efficiency (above 10%) and visible transmittance (above 30%), which makes them potentially suited for lead-free semitransparent solar cell applications.