Bandgap Engineering of Lead-Free Double Perovskite Cs 2 AgBiBr 6 through Trivalent Metal Alloying.

The double perovskite family, A ₂ M ^I M ^III X ₆ , is a promising route to overcome the lead toxicity issue confronting the current photovoltaic (PV) standout, CH ₃ NH ₃ PbI ₃ . Given the generally large indirect band gap within most known double perovskites, band-gap engineering provides an important approach for targeting outstanding PV performance within this family. Using Cs ₂ AgBiBr ₆ as host, band-gap engineering through alloying of In ^III /Sb ^III has been demonstrated in the current work. Cs ₂ Ag(Bi _1-x M _x )Br ₆ (M=In, Sb) accommodates up to 75 % In ^III with increased band gap, and up to 37.5 % Sb ^III with reduced band gap; that is, enabling ca. 0.41 eV band gap modulation through introduction of the two metals, with smallest value of 1.86 eV for Cs ₂ Ag(Bi _0.625 Sb _0.375 )Br ₆ . Band structure calculations indicate that opposite band gap shift directions associated with Sb/In substitution arise from different atomic configurations for these atoms. Associated photoluminescence and environmental stability of the three-metal systems are also assessed.
(© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)