This work proposes gallium oxide grown by plasma-enhanced atomic layer deposition, as a surface passivation material at the CdS buffer interface of Cu(In,Ga)Se₂ (CIGS) solar cells. In preliminary experiments, a metal-insulator-semiconductor (MIS) structure is used to compare aluminium oxide, gallium oxide, and hafnium oxide as passivation layers at the CIGS-CdS interface. The findings suggest that gallium oxide on CIGS may show a density of positive charges and qualitatively, the least interface trap density. Subsequent solar cell results with an estimated 0.5 nm passivation layer show an substantial absolute improvement of 56 mV in open-circuit voltage (V_OC), 1 mA cm⁻² in short-circuit current density (J_SC), and 2.6% in overall efficiency as compared to a reference (with the reference showing 8.5% under AM 1.5G).