Insight into the Impact of Wide Bandgap Transparent Conducting Oxide on the Performance of Thin Film Solar Cells

The excellent optoelectronic properties of transparent conducting oxides (TCOs) are critical for achieving highly efficient thin-film solar cells (TFSCs). In this regard, Mg- and group III-codoped ZnO-based compounds are highly promising TCO materials owing to their wide optical spectra, high transmittance, and electrical properties. However, detailed investigations of TFSC applications remain elusive. In this study, we systematically investigated the detailed relationship between various electrical properties (i.e., carrier concentrations and mobility conditions) and the device parameters for kesterite-based TFSCs. In particular, a quantitative analysis of scattering, detailed Eg-widening mechanisms in TCOs, and their effects on the quantitative deconvolution of series resistance and TFSC performance is discussed. As a result, the photocurrent densities and fill factors in TFSCs are strongly related to the electrical properties of the TCO, whereas the open-circuit voltages remain constant regardless of the TCO material. Among the investigated TCO materials, the Mg and Ga-codoped ZnO TCO layer exhibits favorable band alignment and high transmittance compared with the other layers, significantly enhancing charge transport and suppressing recombination at the interface in TFSC devices. These findings offer new insights into the fundamental impact of wide-optical-bandgap energy TCOs on charge transport, interfacial recombination properties, and overall device performance in inorganic-based TFSC devices.