Structural, Electronic and Optical Properties of Cu 2 Sns 3 Solar Absorber: A First-Principle Density Functional Theory Investigation

Abstract

The development of inexpensive, non-toxic, high efficiency and earth-abundant solar absorbers is critical for terawatt scale implementation of photovoltaics. Cu 2 SnS 3 is a promising earth abundant absorber material that is attracting attention recently for optoelectronic application including photovoltaic solar cells. However, very little is known about the relationship between structural and optical properties such as the absorbance, reflectivity, refractive index, extinction coefficient and energy loss function. These information are however, very essential for the design and fabrication of Cu 2 SnS 3 photovoltaic devices to achieve higher power conversion efficiencies. In this thesis, first-principles calculation based on state-of-the-art methododoly of screened hybrid density functional theory (DFT) have been employed to comprehensively characterize the structural, electronic, and optical properties of Cu 2 SnS 3 material. From band structure analysis, Cu 2 SnS 3 is demonstrated to be a direct band gap materials with a predicted band gap of 0.9 eV, which is in good agreement with available experimental values of 0.9 - 1.3 eV. It is evident from the calculated partial density of states (PDOS) that the anti-bonding Cu-d, Sn-p and S-p states are involved in the transition from valence to conduction band. On the basis of the calculated optical absorbance (in the order 10 5 cm −1 ), reflectivity (approx. 23%), refractive index (approx. 2.90) and extinction coefficient and energy loss function, Cu 2 SnS 3 is demonstrated to be an attractive non-toxic, earth-abundant, and cost- effective material for scalable thin-film PV applications.