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A study on rear passivated thin-CIGS solar cells
S. Suresh (TU Delft - Electrical Engineering, Mathematics and Computer Science)
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Abstract
Having an absorber layer thickness below 1 micrometre for a regular copper indium gallium di-selenide (CIGS) solar cell reduces the pathways for electron collection which lead to reduced recombination in the bulk absorber layer. Additionally, it reduces material costs and production time. Yet, having such a thin absorber reduces the cell efficiency significantly, mainly due to incomplete light absorption and high Mo/CIGS rear-surface recombination . The aim of this research is to implement some innovative rear surface modifications for a <500 nm thick CIGS absorber layer to reduce these effects: a passivation layer to reduce the back-surface recombination and point contact openings using nano-particles (NPs) (CdS, Ag, etc.) to create electrical contacts, with some NPs also improving the optical confinement. For example, one approach is to use a layer of thermally evaporated and uniformly deposited Ag, which is then annealed to create Ag NPs with typical diameters of 300 to 450 nm. An Al2O3 layer is used to passivate the Mo/CIGS rear surface which also prevents the NPs from completely dissolving into the absorber during the absorber deposition. The implementation of all these rear-surface modifications and their impact on the electrical performance of the CIGS solar cell will be discussed and analyzed in this paper. This work received funding from the European Union’s H2020 research and innovation program under grant agreement No. 715027.