Photovoltaic properties of all-inorganic lead-free perovskite Cs 2 PdBr 6 : A first-principles study

Peng Xu 1,a) and Fuxiang Liu 2

AFFILIATIONS

1 Hubei Engineering Research Center of Weak Magnetic-Field Detection, China Three Gorges University, Yichang 443002, China

2 College of Science and TGMRC, China Three Gorges University, Yichang 443002, China

a) Author to whom correspondence should be addressed: xupeng@ctgu.edu.cn

ABSTRACT

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 Cs 2 PdBr 6 as a narrow bandgap semiconductor with long-term stability has attracted great attention. Herein, through performing first-principles calculations, we find that (i) Cs 2 PdBr 6 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 Cs 2 PdBr 6 and popular perovskites indicate that Cs 2 PdBr 6 is more difficult to be doped p-type according to the doping limit rule. The commonly used electron transport materials such as TiO 2 ,SnO 2 , ZnO, and C 60 can also be suitable for Cs 2 PdBr 6 solar cell devices, but the commonly used hole transport materials with a lower highest occupied molecular orbital is an alternative. (iii) Cs 2 PdBr 6 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 Cs 2 PdBr 6 as a solar cell absorber.