Use of a precursor solution to fill the gaps between indium tin oxide nanorods, for preparation of three-dimensional CuInGaS2 thin-film solar cells

We have fabricated a three-dimensional (3D) nanostructured indium tin oxide (ITO) film in which the spaces were filled by use of a Cu, In, and Ga precursor solution. This solution has potential for use in bulk heterojunction CuInxGa1−xS2 (CIGS) thin-film solar cells. ITO nanorod films ~700 nm thick on glass substrates were synthesized by radio-frequency magnetron sputtering deposition. To ensure complete filling of the gaps in ITO nanorod films, a polymeric binder-free precursor solution was used. In addition, a two-step heating process (oxidation and sulfurization) was used after coating of the precursor solution to make a CIGS absorber film with a minimum of carbon impurities. Superstrate-type solar cell devices with 3D nanostructured films (CIGS–ITO) had a photovoltaic efficiency of 1.11 % despite the absence of a buffer layer (e.g. CdS) between the CIGS and ITO.