Structural and optical characteristics of Sn-doped CuGaSe2 thin films as a new intermediate band material for high-efficiency solar cells

In this research, a new intermediate band (IB) material Sn-doped CuGaSe2 was synthesized for light absorbing layers of high-efficiency solar cells via ball milling. The experimental investigation indicated that element Sn can be successfully doped in the chalcopyrite CuGaSe2 sample, which enhanced the absorption spectrum significantly in the range of visible and near-infrared light wavelength (500 nm-900 nm). With the increase in the content of Sn, the optical bandgap of CuGa1-xSnxSe2 thin films was tuned from 1.65 eV to 1.41 eV for the doping content x from 0.00 to 0.06. The above results proved that the IB was introduced into the CuGa1-xSnxSe2 thin films, and due to the IB existence, this material leads to lower-energy photo absorption (with energy h nu <= 1.68 eV). Moreover, the presence of Sn4+ in the host material was testified by x-ray photoelectron spectroscopy. Element composition and mapping analysis further confirmed that the fabricated film is composed of Cu, Ga, Sn, and S, and all elements have a homogeneous distribution without partial aggregation. Photoelectric investigations of the Sn-CuGaSe2 indicated that it is a desirable and promising IB material, which could be another candidate for light absorption layers of high-efficiency solar cells.