Effect of Li + Doping on Photoelectric Properties of Double Perovskite Cs 2 SnI 6 : First Principles Calculation and Experimental Investigation.

Double perovskite Cs 2 SnI 6 and its doping products (with SnI 2 , SnF 2 or organic lithium salts added) have been utilized as p-type hole transport materials for perovskite and dye-sensitized solar cells in many pieces of research, where the mechanism for producing p-type Cs 2 SnI 6 is rarely reported. In this paper, the mechanism of forming p-type Li + doped Cs 2 SnI 6 was revealed by first-principles simulation. The simulation results show that Li + entered the Cs 2 SnI 6 lattice by interstitial doping to form strong interaction between Li + and I - , resulting in the splitting of the α spin-orbital of I-p at the top of the valence band, with the intermediate energy levels created and the absorption edge redshifted. The experimental results confirmed that Li + doping neither changed the crystal phase of Cs 2 SnI 6 , nor introduced impurities. The Hall effect test results of Li + doped Cs 2 SnI 6 thin film samples showed that Li + doping transformed Cs 2 SnI 6 into a p-type semiconductor, and substantially promoted its carrier mobility (356.6 cm 2 /Vs), making it an ideal hole transport material.