Structural, Electronic, and Optical Properties of Cu2sns3 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. Cu2SnS3 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 fabrica- tion of Cu2SnS3 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 compre- hensively characterize the structural, electronic, and optical properties of Cu2SnS3 material.
From band structure analysis, Cu2SnS3 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 105 cm−1), reflectivity (approx. 23%), refractive index (approx. 2.90) and extinction coefficient and energy loss function, Cu2SnS3 is demonstrated to be an attractive non-toxic, earth-abundant, and cost- effective material for scalable thin-film PV applications.
INTRODUCTION
The growing need for energy by our society and the depletion of conventional energy sources, coupled with the challenge to ameliorate climate change, demands the development and improvement of safe, renewable and low-cost clean energy technologies.
By far the most abundant renewable energy source comes from the sun: the total amount of incident solar radiation on Earth’s surface 1.4×1017 W.
Covering just 1% of the earth’s surface with photovoltaic (PV) modules operating with 10% efficiency would produce around 25 TW.
Thus, the development of low cost and efficient photovoltaic (PV) technologies is critical for providing energy to the growing world population and combating man-made climate change.
Photovoltaic technology which makes use of the super-abundant and freely available Sun’s energy to gener- ate electricity has obvious economic, environmental and societal benefits. However, in order for PV technology to provide a significant fraction of the world’s energy demands, devices must be composed of cheap and readily available materials.
Science and engineering are in a unique position to address the challenge to discover, design and develop cheap, non-toxic, and earth-abundant new materials that exhibit the ideal electronic properties for PV applications.
Issues facing traditional photovoltaics
By far the most well studied and commercially successful PV absorber is silicon. De- velopment proceeded rapidly, largely because researchers could draw on the extensive Si processing experience of the microelectronics industry.
Silicon has maintained its dominance to the present day: as of 2013, more than 80% of the photovoltaics industry was based on Si wafer technologies.
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