EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Thin-film photovoltaic (PV) technologies, and Cu(In,Ga)Se2 (CIGS) thin-film solar cells in particular, have been the subject of increasingly rigorous study of late. There are several motivating factors for the development of thin-film photovoltaics, such as reduction in raw material usage, decrease in cell weight, and the possibility of deposition on flexible substrates. Furthermore, CIGS-based thin-film solar cells hold several advantages compared to rival solar cell technologies. Specifically, they have the highest conversion efficiencies among chalcogenide thin-film PV technologies (23.35% for cells, 17.5% for modules), high radiation resistance, and outstanding stability.

The typical CIGS-based solar cell consists of a soda-lime glass (SLG) substrate, a Mo back contact, CIGS as the p-type absorber layer, CdS as the n-type buffer layer, and ZnO/ZnO:Al as the decoupling and transporting window layers, respectively. However, in the state-of-the-art CIGS-based solar cells, each of these layers is deposited with a different method; co-evaporation for the CIGS layer, chemical bath deposition for the CdS layer, and reactive sputtering for the ZnO/ZnO:Al bilayer.

This work reports on the utilization of pulsed laser deposition (PLD) as a single technique for the preparation of the aforementioned layers of a complete CIGS-based solar cell. The properties of the PLD-grown films with respect to structure, composition and morphology are parametrically investigated. Hence, the influence of PLD parameters on film growth is evaluated. TCAD simulations are utilized for the optimization of the cell function. Electrical and optical measurements are used to assess the photovoltaic behavior of the complete structure and, critically, the CdS/CIGS junction heterointerface. The solutions implemented, involving modifications to the typical PLD process, are discussed. Finally, the resulting improvement in conversion efficiency is demonstrated.