Proceedings of MATSUS Fall 2023 Conference (MATSUSFall23)
Publication date: 18th July 2023
A tandem solar cell is a structure that combines two or more absorber layers with different band-gap to enhance light absorption. Among various combinations for tandem solar cells, CIGS/Perovskite tandem solar cells have the advantage of using high-performance perovskite solar cells as the top cell and CIGS solar cells as the bottom cell [1], which can easily achieve current matching. Cu(In,Ga)Se2 (CIGS) solar cells use a quaternary compound thin film of copper, indium, gallium, and selenium elements, which has a high light absorption coefficient. By controlling the Ga content within the absorber layer, the bandgap can be tuned from 1.0 to 1.7 eV. Normally, CIGS solar cells with high conversion efficiency have a bandgap between 1.1 and 1.2 eV, but this bandgap range is not suitable for tandem solar cells, as the perovskite absorber layer as the top cell would have to use a wide bandgap. To achieve proper current matching, a CIGS absorber layer with a low bandgap is needed as the bottom cell. In this study, we fabricated a CIGS absorber layer with a low bandgap for the bottom cell. A Ga element was deposited on the prepared substrate and the CuInSe2 absorber layer was formed by a three-stage co-evaporation process. The thickness and annealing temperature of the absorber layers were controlled to verify the Ga distribution. Depth profiling analysis confirmed the diffusivity of internal Ga diffusion depending on the process temperature and the thickness of the CIGS absorber layer. In addition, when the bandgap was measured by EQE, there was no change in the bandgap despite the presence of Ga. When a device was fabricated using the prepared absorber layer and the device efficiency was measured, it was confirmed that the open-circuit voltage improved compared to CIS solar cell devices.
This work was supported by the DGIST R&D Program of the Ministry of Science and ICT (23-ET-08) and the DGIST R&D Programs of the Ministry of Science, ICT & Future Planning of Korea (22-CoE-ET-01)
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