20% Efficient Zn0.9Mg0.1O:Al/Zn0.8Mg0.2O/Cu(In,Ga)(S,Se)(2) Solar Cell Prepared by All-Dry Process through a Combination of Heat-Light Soaking and Light-Soaking Processes

Development of Cd-free Cu(In,Ga)(S,Se)(2) (CIGSSe)-based thin-film solar cells fabricated by an all-dry process is intriguing to minimize optical loss at a wavelength shorter than 520 nm owing to absorption of the CdS buffer layer and to be easily integrated into an in-line process for cost reduction. Cd-free CIGSSe solar cells are therefore prepared by the all-dry process with a structure of Zn0.9Mg0.1O:A1/Zn0.8Mg0.2O/CIGSSe/Mo/glass. It is demonstrated that Zn0.8Mg0.20O and Zn0.9Mg0.1O:Al are appropriate as buffer and transparent conductive oxide layers with large optical band gap energy values of 3.75 and 3.80 eV, respectively. The conversion efficiency (eta) of the Cd-free CIGSSe solar cell without K-treatment is consequently increased to 18.1%. To further increase the eta the Cd-free CIGSSe solar cell with K-treatment is next fabricated and followed by posttreatment called the heat-light-soaking (HLS) + light-soaking (LS) process, including HLS at 110 degrees C followed by LS under AM 1.5G illumination. It is disclosed that the HLS + LS process gives rise to not only the enhancement of carrier density but also the decrease in the carrier recombination rate at the buffer/absorber interface. Ultimately, the eta of the Cd-free CIGSSe solar cell withK-treatment prepared by the all-dry process is enhanced to the level of 20.0%.