Composition effects on structure and optical properties in double perovskite derivatives semiconductors Cs2SnI6−xBrx (x = 0–6)

We have proved that Cs2SnI6−xBrx (x = 0–6) can be eutectic in the whole composition, and the eutectic phase has the similar cubic symmetry with both of the end phases (space group of Fm3¯m). The lattice constant decreases from around 11.67 Å (x = 0) to around 10.83 Å (x = 6). Hall-plot analysis shows that the strain varies sharply near the two end materials, while the strain is almost independent of Br content at the middle Br content. The bandgap, on the other hand, increases from 1.26 eV to 2.93 eV with increasing the Br content, which might be expected in fabricating the continuous junction solar cells.