  Halide double perovskites have recently been proposed as potential
environmentally friendly alternatives to organic group and lead based hybrid
halide perovskites. In particular, Cs2BiAgX6 have been synthesized and found to
exhibit tunable band gaps in the visible range. However, the band gaps of these
compounds are indirect, not ideal for applications in thin film photovoltaics.
Here in this work we have carried out systematic modelling, using a materials
genome approach in the framework of the density functional theory (DFT), to
formulate a new system of solar absorption layer based on Cs2InAgX6 and its
heterojunction device. Through Cl partial substitution on Br in Cs2InAgBr6 to
optimize its thermodynamic stability after the calculation of ATAT proportion
searching and Gibbs free energy, we have identified a series of stable cubic
structured phases, with the general formula of Cs2AgInBr(6-x)Clx, as remarkable
solar absorption layer to enable harvesting the solar energy. The optimized
Cs2InAgBr5Cl compound is a marvellous solar absorption layer, with direct 1.92
eV bandgap and high solar absorption ability, consistent with Cs2InAgBr6 at
standard room temperature (298 K). Assembling with anatase as n type TCO and
Cs6Ag4In4Br18Cl4 as p type TCO fabricated by introducing Cs_Br defect, the
heterojunction is integrated into PSCs based on the standard pin structure
(TiO2_Cs2InAgBr5Cl_Cs6Ag4In4Br18Cl4), the lattice mismatching, microscopic
function and band offset are evaluated for this well designed device.
