Abstract
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 hν ≤ 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.
Highlights
An innovative concept of intermediate band solar cells (IBSCs) was proposed to significantly extend the absorption spectrum increasing the photovoltaic conversion efficiency
We have investigated the synthesis of Sn-doped CuGaSe2 thin films by a facile non-vacuum solution with ball milling, spin-coating, and annealing
Diffraction peaks shift toward lower angles, which suggests that the Ga sites in CuGaSe2 were likely substituted by some Sn atoms for the larger Sn ionic radii, which caused the lattice expansion
Summary
An innovative concept of intermediate band solar cells (IBSCs) was proposed to significantly extend the absorption spectrum increasing the photovoltaic conversion efficiency. A proper located intermediate band (IB) in the intrinsic bandgap serves as a “stepping stone,” allowing photons with energies below the bandgap to excite from the VB to the conduction band (CB) via a two-step process. Due to these additional excitation channels, IBSCs have the highest theoretical conversion efficiency (63.2%), greater than the single bandgap cells (40.7%).. If an IB is created inside the bandgap, CuGaSe2 could be another promising candidate material for IBSCs. there are few reports on CuGaSe2 acting as an IB host semiconductor material, including theoretical studies
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