Sulfur is extensively used to increase the bandgap of Cu(In,Ga)(S,Se)2(CIGSSe) solar cells and to improve the open circuit voltage (VOC) in order to optimize the characteristics of the devices. This study uses a sulfurization process to obtain a double-graded bandgap profile. Selenization was carried out on Cu(In,Ga) precursors, followed by one sulfurization process or two consecutive sulfurization processes on top of the CIGSe absorber layer surface. The optimum two-step sulfurization process provides an increase of VOCof 0.05 V and an improvement of conversion efficiency of 1.17%. The efficiency of the 30 × 30 cm2monolithic module, which has 64 CIGS cells connected in series (aperture area: 878.6 cm2), is 15.85%. The optical and electrical properties of the phase and the work function distribution were investigated using the depth profiles of the absorber layer as a function of the sulfurization conditions. The CIGSSe thin film formed by two-step sulfurization with a high sulfur concentration exhibits a single work function peak, better crystallinity, and higher conversion efficiency than those of the thin film formed by two-step sulfurization at low sulfur concentration. In terms of the Raman spectra depth profile, the phase areas for the CIGSSe thin film that underwent the optimized high sulfur concentration two-step-sulfurization appeared to have less of Cu2-xSe phase than that with low sulfur concentration. Consequently, surface and interface phase analysis is an essential consideration to improve cell efficiency.
|Number of pages||10|
|Journal||Progress in Photovoltaics: Research and Applications|
|State||Published - 1 Feb 2017|
Bibliographical noteFunding Information:
This work was supported by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), with a grant funded by the Korea government, Ministry of Trade, Industry and Energy (No. 20123010010130).
Copyright © 2016 John Wiley & Sons, Ltd.
- bandgap grading
- CIGSSe solar cell
- Kelvin probe force microscopy
- Raman scattering spectroscopy