First-principles study on the structural, mechanical, and optoelectronic properties of Sn doped Cs2ZrI6 double perovskites

Lead-free all-inorganic double perovskites have attracted much attention due to their environmentally friendly and excellent photoelectric performance. Cs2ZrI6, as a novel non-toxic double perovskite absorption layers material, has an intrinsic wide indirect bandgap nature, which undoubtedly has a significant negative impact on the photoelectric conversion efficiency. This study demonstrates that by adjusting the doping concentration of Sn in Cs2ZrI6 double perovskite, the photoelectric performance has been improved. The Sn-doped double perovskite Cs2Zr1-xSnxI6 (0 <= x <= 1) is structural and mechanical stability, as well as good mechanical ductility, which is beneficial for the application of flexible photoelectric devices. Electronic structure calculations showed that the bandgap of Cs2Zr1-xSnxI6 changes from indirect to direct when the doping ratio is 25 % (x = 0.25), and accompanied by bandgap narrowing with the increase of Sn doping concentration. When the concentration was increased to 50 % and 75 %, the bandgap value decreases to 1.52 eV and 1.27 eV respectively, which exactly reaches the optimal bandgap required by the Shockley-Queisser efficiency limit. Moreover, the optical absorption coefficient in the visible region gradually improves with the increase of Sn doping concentrations, and the absorption coefficient in the near ultraviolet region reaches 10(5)cm(-1). Therefore, the narrow direct bandgap at x = 0.25 and 0.75 increases their potential as the absorption layers of single-junction perovskite solar cells at specific composition.