Defect Engineering and Admittance Spectroscopy Study of CZTSSe Solar Cells
Date Issued
2016
Date
2016
Author(s)
Lin, Yi-Rung
Abstract
In the past decades, numerous promising solar cell concepts, ranging from single-crystallized silicon to thin-film based technologies, have been developed and are being studied intensely by an increasing number of scientific groups and companies. Within the thin-film based photovoltaic technology, kesterite-based Cu2ZnSn(S,Se)4 (CZTS) photovoltaics, which is the analogous of Cu(In,Ga)(S,Se)2 (CIGS) photovoltaics, has emerged as a potential candidate absorber material for the next generation thin film solar cells due to their advantages of earth-abundance and low-cost requirements. Compared with CIGS photovoltaics, the earth abundant zinc and the rare and expensive tin replaces indium and gallium in the CZTS absorber. In spite of the latest demonstration of solution-processed CZTS devices over 12% power conversion efficiency, the development of CZTS as an absorber material is still behind in terms of both fundamental understanding of the material system and in the capability to precisely control the formation of MoSe2 layer underneath of the absorber CZTS and Mo substrate for high-efficiency CZTS device, as compared with those of CIGS and CdTe. Therefore, this dissertation targets three key areas in this field: (1) Defect characterization and its relationship to carrier dynamics; (2) Modification of the interface of CZTS/Mo to reduce the formation of MoSe2 in order to improve the device performance and (3) Solution-processing with environmentally friendly solvents for large-scale production. For starters, we explored various precursor systems, such as benign organic solvents, nano-metallic particles, and have successfully processed CZTS from a molecular solution in a benign solvent system. A homogeneous precursor solution has also been developed and proved to offer more precise phase and composition control. Moreover, the high-efficiency CZTS solar cell has also been developed by vacuum-based sputter system. In this work we further investigated an effective buffer layer to improve the carrier transport behaviors. Furthermore, a promising technique – Bifacial sodium-incorporated treatment – has been applied in the CZTS solar cells to manipulate the defect properties and the relating device performance. Lastly, by using electrical and optical characterization, we have conducted detailed investigations on the bulk and the interface defects that govern the carrier recombination and the resulting device characteristics. Aforementioned results reveal the effects of the alkali metals in CZTS and the importance of interface of CZTS/Mo on the defect concentration and on carrier dynamics of the solar cells.
Subjects
Cu2ZnSnS4
Solar cell
Defect engineering
Carrier dynamics
Admittance spectroscopy
Impedance spectroscopy
SDGs
Type
thesis
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