Absorber Delamination-Induced Shunt Defects in Alcohol-Based Solution-Processed Cu(In,Ga)(S,Se)₂ Solar Modules

Solution-processed chalcopyrite Cu(In,Ga)(S,Se)2 (CIGSSe) solar modules are promising alternatives to conventional crystalline silicon-based photovoltaic devices owing to their potential to lower production costs and compatibility with large-area flexible substrates. However, these modules typically exhibit a higher-than-expected cell-to-module loss, which, in most cases, is attributed to the emergence of critical shunt sites. In this study, we investigated the structural shunt defects induced by delamination of the absorber in alcohol-based solution-processed CIGSSe solar modules. Characterization with the use of lock-in thermography indicated that most of the delamination-induced shunt defects emerged locally near the patterned regions. Furthermore, secondary-ion mass spectroscopy measurements showed that, rather than being uniformly distributed, the alkali elements in the CIGSSe modules were concentrated near the patterned regions. The results revealed that the uniformity of this distribution is the key driving force behind absorber delamination. Finally, we confirmed that delamination-induced shunt defects can be alleviated by controlling the diffusion of alkali elements. Consequently, the energy conversion efficiency of the alcohol-based solution-processed CIGSSe solar modules was enhanced from 4.24 to 7.59% by introducing a layer that acts as a thin-film diffusion barrier.