Abstract
In view of the large-scale utilization of Cu(In,Ga)Se2 (CIGS) solar cells for photovoltaic application, it is of interest not only to enhance the conversion efficiency but also to reduce the thickness of the CIGS absorber layer in order to reduce the cost and improve the solar cell manufacturing throughput. In situ and real-time spectroscopic ellipsometry (RTSE) has been used conjointly with ex situ characterizations to understand the properties of ultrathin CIGS films. This enables monitoring the growth process, analyzing the optical properties of the CIGS films during deposition, and extracting composition, film thickness, grain size, and surface roughness which can be corroborated with ex situ measurements. The fabricated devices were characterized using current voltage and quantum efficiency measurements and modeled using a 1-dimensional solar cell device simulator. An analysis of the diode parameters indicates that the efficiency of the thinnest cells was restricted not only by limited light absorption, as expected, but also by a low fill factor and open-circuit voltage, explained by an increased series resistance, reverse saturation current, and diode quality factor, associated with an increased trap density.
Highlights
Cu(In,Ga)Se2 (CIGS) is one of the most promising materials for obtaining low-cost and high-efficiency thin-film solar cells viable for large-scale production
We focus on the growth process of CIGS films for various thicknesses (1.95 μm to 0.35 μm) characterized by in situ real-time spectroscopic ellipsometry (RTSE), and the results are correlated with ex situ measurements Journal of Spectroscopy
We have demonstrated the use of RTSE for real-time monitoring and control of thin-film CIGS deposition [22]
Summary
Cu(In,Ga)Se2 (CIGS) is one of the most promising materials for obtaining low-cost and high-efficiency thin-film solar cells viable for large-scale production. In the case of CIGS, many manufacturers are paving the way for GW-scale production capacity. As CIGS technology continues to increase its share of the market, the scarcity and high price of indium may potentially affect its ability to compete with other technologies. One way to avoid this bottleneck is to reduce the importance of indium and gallium in the fabrication of the cell by reducing CIGS thickness without significant loss in its efficiency. The potential advantages of this concept derive from the reduction of cost and usage of materials (especially In and Ga) and the increase in production throughput
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