To investigate the origin of the Na effect on photovoltaic (PV) devices, Cu(In,Ga)Se2 (CIGS) and CdS/CIGS layers were grown on borosilicate (BS) and soda-lime glass (SLG), respectively. The defect states and nonequilibrium carrier dynamics of the samples were measured using photoluminescence (PL) and optical pump-THz probe (OPTP) spectroscopy. From the PL results, we discovered that different shallow donor-acceptor levels were formed in the CIGS layer grown on BS and SLG, respectively. In the OPTP results, relaxation times of photocarriers excited from the CdS/CIGS layer were clearly distinguishable, and are explained by the formation of different defect states depending on substrates. In BS, deep defect level 'DX states' were formed in the Eg near the p-n junction, which induce trapping photocarriers, resulting in shortening relaxation time. In SLG, there was no "DX state", which clearly demonstrates the positive effect of Na atoms at the p-n junction on performance of PV devices.
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© 2015 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films