Fig. 8 shows the as-measured reflectance spectra of CuO and
Cu2O films. Here, the incident angle of beam is 858 to the film
surfaces. The Cu2O films have distinct characteristics in 300–
590 nm range whereas, CuO films do not exhibit such a peak in this
wavelength range. Similar results have been observed for Cu2O
films synthesized by thermal oxidation of copper [26]. The
reflectance of both films is lower than 40% except for the peak
value of Cu2O film. The reflectance spectra may be influenced by
the surface roughness of the films. In this case, both films are
coated under the same conditions and heated at different
temperatures. The average surface roughness of CuO and Cu2O
films obtained with AFM measurements were 18 nm and 22 nm,
respectively. These differences can influence the low reflectance of
CuO films in UV and visible range of the spectrum. In thin film
devices, such as solar cells, the optical reflectance plays a key role
on energy conversion efficiency. Typically, the high bandgap-Cu2O
layers can be employed in the top layers of solar cells while low
gap-CuO layers can be used as the absorption layers (bottom) of
solar cells. Therefore, the reflectance spectra of Cu2O films can be
considered as a key parameter in feasibility investigation of Cu2O
films for solar cell applications.