Long term stability and recovery of 3 MeV proton irradiated Cu(In,Ga)Se2 and Cu2(Zn,Sn)(S,Se)4 thin film solar cells

In 2017, Cu(In,Ga)Se2 (CIGS), Cu2(Zn,Sn)S4 (CZTS) and Cu2(Zn,Sn)(S,Se)4 (CZTSSe) thin film solar cells were irradiated by our group using 3 MeV protons to investigate the materials’ radiation hardness and subsequent recovery following dark storage. It was observed that the primary losses were in open-circuit voltage (VOC), with the CZTS and CZTSSe being more resistant than the CIGS, also recovering to ∼ 95% of initial performance, compared to ∼ 70% for CIGS after two months dark storage. In 2021 the cells were investigated by external quantum efficiency and current-voltage measurements once again, to investigate further recovery. The CIGS cells had continued to recover, whilst the CZTSSe devices appear to have fully recovered from radiation induced damage, but now suffer from aging-related degradation and exhibit slight bandgap widening over time. The CZTS cells were observed to recover fully from the radiation induced damage, whilst also showing gains in VOC.