Photovoltaic properties of all-inorganic lead-free perovskite Cs2PdBr6: A first-principles study

Lead halide perovskite has shown amazing optoelectronic performance, while the issues of its toxicity and the thermal instability remain to be intractable. Recently, lead-free halide perovskite Cs2PdBr6 as a narrow bandgap semiconductor with long-term stability has attracted great attention. Herein, through performing first-principles calculations, we find that (i) Cs2PdBr6 has a quasi-direct bandgap with an indirect bandgap of 1.71 eV and a 20 meV smaller direct bandgap. The bandgap increases when the lattice constant enlarges, which is opposite to that of the traditional zincblende semiconductors. (ii) Band offsets between Cs2PdBr6 and popular perovskites indicate that Cs2PdBr6 is more difficult to be doped p-type according to the doping limit rule. The commonly used electron transport materials such as TiO2, SnO2, ZnO, and C60 can also be suitable for Cs2PdBr6 solar cell devices, but the commonly used hole transport materials with a lower highest occupied molecular orbital is an alternative. (iii) Cs2PdBr6 is shown to be difficult to be intrinsic p-type. The electric conductivity would not be too high due to the charge compensation of the defects if there is no suitable external doping. Since the Pd poor and Br rich condition can suppress the formation of the defects with deep levels, this condition is proposed to synthesize Cs2PdBr6 as a solar cell absorber.