The systematic variations in the structural, optical, and electrical properties of polycrystalline $\text{Cu}\left(\text{In},\text{Ga}\right){\text{Se}}_2$ (CIGS) thin films with Na doping level were investigated. Precise control of the Na concentration in CIGS films was demonstrated using alkali-silicate glass thin layers of various thicknesses deposited on substrates prior to CIGS growth. The CIGS grain size was observed to decrease with increasing Na concentration, although the surface morphology became smoother and exhibited a stronger (112) texture, which has been demonstrated consequence of larger grain size. The Ga composition gradient in the CIGS films was found to become large due to the presence of Na during growth, which in turn led to a decrease in the nominal band gap energy. Variations in the photoluminescence spectra and electrical properties suggested that the formation of an acceptor energy state, which may originate from ${\text{O}}_{\text{Se}}$ point defects, was enhanced in the presence of Na. This result suggests that not only Na, but also the presence of O in combination with Na contributes to the compensation of point defects and enhances $p$ -type conductivity in CIGS films.

Hole traps in $p$ -type ${\mathrm{Cu}}_2\mathrm{O}$ were studied by means of deep level transient spectroscopy in the heterostructure of $p\text{-}{\mathrm{Cu}}_2\mathrm{O}∕i\text{-}\mathrm{ZnO}∕n\text{-}\mathrm{ZnO}$ . In addition to the trap level at about $0.45\mathrm{eV}$ from the valance band edge, which is already reported as being due to Cu vacancy, we found a new trap level at about $0.25\mathrm{eV}$ . The new trap is tentatively assigned as Cu-di-vacancy from the trap concentration dependence on oxygen flow rate and substrate temperature.