Source Material Design for Realizing >50% Indium-Saving Transparent Electrode toward Sustainable Development of Silicon Heterojunction Solar Cells.

Indium (In) reduction is a hot topic in transparent conductive oxide (TCO) research. So far, most strategies have been focused on reducing the layer thickness of In-based TCO films and exploring TCOs. However, no promising industrial solution has been obtained yet. In our work, we adopt the emerging reactive plasma deposition (RPD) approach and provide our solution by directly reducing the In content from the source material. We designed the indium zinc oxide (IZO) target with a composition of ZnInO (i.e., (ZnO)·InO). Density functional theory (DFT) calculation shows that the introduction of a large amount of ZnO significantly perturbs the conduction band of the InO host, resulting in a limitation of exploring high-mobility IZO films. For TCOs used in solar cell application, low resistivity with high carrier mobility is required. Via RPD process optimization, we obtained the minimal resistivity value of 6.08 × 10 Ω·cm, which is comparable to our lab-standard tin-doped indium oxide (ITO) film. The corresponding electron mobility and carrier concentration are 31 cm V s and 3.37 × 10 cm, respectively. Our IZO film is in an amorphous state. The optical band gap is ∼3.6 eV. X-ray photoelectron spectroscopy (XPS) data show that the film composition is In:Zn:O = 21.60:28.75:49.65 (at. %). Damp heat tests show strong stability of our IZO film, and no aging effects have been observed. Furthermore, we demonstrated wafer-scale silicon heterojunction (SHJ) solar cells with IZO films. As compared with our reference hydrogenated cerium-doped indium oxide (ICO)-based solar cells, the IZO-based devices show even higher fill factor parameters. Our amorphous state stable IZO film could find versatile application in the sustainable development of temperature-sensitive devices such as SHJ and perovskite/silicon tandem solar cells, as well as flexible OLEDs.