Enhancement of photovoltaic performances of Cu (In,Ga)(S,Se) 2 solar cell through combination of heat‐light soaking and light soaking processes

Potassium‐treated Cu (In,Ga)(S,Se) 2 (CIGSSe)‐based solar cell with power conversion efficiency (η) of 19.4% is obtained using high transparent Cd 0.75 Zn 0.25 S/Zn 0.79 Mg 0.21 O/Zn 0.88 Mg 0.12 O:Al layers to minimize optical loss at short wavelength (~520 nm) and to control total conduction band minimum alignment. To further enhance η, the post treatment named HLS + LS process, including heat‐light soaking (HLS) at 110°C under AM 1.5G illumination followed by light soaking (LS) under AM 1.5G illumination, is conducted successively on the as‐fabricated solar cell. It is revealed that HLS in the HLS + LS process mainly yields the increase in open‐circuit voltage. On the other hand, LS in the HLS + LS process primarily leads to the increase in fill factor, attributable to the decrease in sheet resistance of Zn 0.88 Mg 0.12 O:Al. The HLS + LS process consequently gives rise to not only the enhancement of carrier concentration but also the decrease in the recombination rate at the buffer/absorber interface through passivating the recombination centers. As a result, 21.2%‐efficient CIGSSe solar cell with the Cd 0.75 Zn 0.25 S/Zn 0.79 Mg 0.21 O/Zn 0.88 Mg 0.12 O:Al layers is attained after the HLS + LS process, which is an effective process to enhance photovoltaic performances.