Aging Effect of a Cu(In,Ga)(S,Se)_2 Absorber on the　Photovoltaic Performance of Its Cd-Free Solar Cell Fabricated　by an All-Dry Process: Its Carrier Recombination Analysis

摘要

Cd-free Cu(In,Ga)(S,Se)(2) (CIGSSe) solar cells are fabricated by an all-dry process (a Cd-free and all-dry process CIGSSe solar cell) with aged CIGSSe thin film absorbers. The aged CIGSSe thin films are kept in a desiccator cabinet under partial pressure of oxygen of approximate to 200 Pa for aging time up to 10 months. It is reported for the first time that aged CIGSSe thin film with increased aging time results in significant enhancement of photovoltaic performance of Cd-free and all-dry process CIGSSe solar cells, regardless of the alkali treatment. Based on carrier recombination analysis, carrier recombination rates at the interface and in the depletion region of the Cd-free and all-dry process CIGSSe solar cells are reduced owing to avoidance of sputtering damage on CIGSSe absorber surface, which is consistent with the strong electron beam-induced current signal near CIGSSe surface after the increased aging time. It is implied that the interface and near-surface qualities are clearly improved through the increased aging time, which is attributable to the self-forming of In-x(O,S)(y) near CIGSSe surface, which acts as a buffer layer. Ultimately, the 22.0%-efficient Cd-free CIGSSe solar cell fabricated by all-dry process is achieved with the aged Cs-treated CIGSSe absorber with the aging time of 10 months.