Fabrication of Transparent ITO/Ga-Doped ZnO Coating as a Front Panel Electrode toward Efficient Thin Film Solar Cells

Bi-layer coatings from sputtered indium tin oxide (ITO) and gallium doped zinc oxide (Ga:ZnO) were investigated for transparency in the visible range of the electromagnetic spectrum, optical rejection ability in the near infrared spectrum and conductivity for the novel quantum dot based solar cells. The multilayer stack with optimized films thickness and surface roughness exhibit improved optical properties without to worsen the electrical ones, especially after additional oxidation during reactive sputtering of the metal-oxides. With an average optical transmittance of 90.7% over the visible region, average optical rejection greater than 65 % in the infrared range and resistivity lower than 100 Ω.cm, this coating is good candidate for front panel in CdS/ZnS core-shell quantum dots based solar cells. The efficiency of the cell increased with approximately 3 % as compared to the case with ITO only electrode. The results might be ascribed to the relatively low surface roughness and to the narrowed transmittance spectrum after ITO/Ga:ZnO interface has been established, targeting absorption of visible light only.