Characteristics of Ga-Rich Cu(In, Ga)Se₂ Solar Cells Grown on Ga-Doped ZnO Back Contact

Wide bandgap Cu(In, Ga)Se₂ (CIGS) thin films were deposited on Ga-rich Ga:ZnO (GZO) or MoN/GZO by single-stage co-evaporation. CIGS/TCO interface phases, such as resistive n-type Ga₂O₃, which are likely to have formed during the high temperature growth of Ga-rich CIGS, can deteriorate the solar cell performance. Although some Ga accumulation was observed in both of the CIGS/GZO and CIGS/MoN/GZO interfaces formed at 520 °C, the Ga oxide layer was absent. On the other hand, their current–voltage characteristics showed strong roll-over behavior regardless of the MoN diffusion barrier. The strong Schottky barrier formation at the CIGS/GZO junction due to the low work function of GZO, was attributed to current blocking at a high forward bias.