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Na-Dependent Ultrafast Carrier Dynamics of CdS/Cu(In,Ga)Se2 Measured by Optical Pump-Terahertz Probe Spectroscopy
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- Authors
- Woo-Jung Lee, Dae-Hyung Cho, Jae-Hyung Wi, Won Seok Han, Yong-Duck Chung, Jaehun Park, Jung Min Bae, Mann-Ho Cho
- Issue Date
- 2015-07
- Citation
- The Journal of Physical Chemistry C, v.119, no.35, pp.20231-20236
- ISSN
- 1932-7447
- Publisher
- American Chemical Society(ACS)
- Language
- English
- Type
- Journal Article
- Abstract
- 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.
- KSP Keywords
- CIGS layer, Defect level, Na effect, Optical pump-terahertz probe(OPTP), Optical pump-terahertz probe spectroscopy, P-N junction, Petri net(PN), Relaxation time, Shallow donor, Soda lime glass(SLG), Ultrafast carrier dynamics