Abstract
This work is dedicated to theoretically investigating the mixed-halide direct band gap organic-inorganic hybrid double perovskites (OIHdPs), MA2AgIn(BrxI1-x)6, with and without anion vacancy point (AVP) defects. We calculate their structural and optoelectronic properties with different halide compositions and find that the effect of halide composition on the properties of MA2AgIn(BrxI1-x)6 is quite different from that on lead-bearing perovskites. All the vacancy-free I-bearing systems (x ≠ 1) have nearly the same direct band gap width and carrier activity with MAPbI3. The Br-rich systems (x > 0.50) are relatively thermodynamical stable and not prone to spontaneous anion segregation and show a strong "self-tolerance" feature toward the inherit defects as well. With these distinguished properties, we are able to conclude that MA2AgIn(BrxI1-x)6 with 0.50 < x < 1 are promising candidates for Pb-free photovoltaic materials. This Letter provides a detailed microscopic understanding of the vacancy-induced band distortion in lead-free heterovalent substitution OIHdPs and has some guiding significance for molecular design of nontoxic photovoltaic materials.
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