Eliminating Mobility-Thickness Dependence in Transparent Conductive Oxide Layer Growth: A Critical Nucleation Strategy

Abstract

Carrier mobility is a key parameter for transparent conductive oxide (TCO) layers. However, it shows significant thickness-dependent deterioration in the reports so far, making it challenging to obtain high-quality ultrathin TCO films. Here, a critical nucleation strategy (cns) is proposed, i.e., manipulating nucleation status that matches the intended film thickness, to break the spell. 30, 20, and 10 nm-thick cerium-doped indium oxide (ICO) films are successfully fabricated with electron mobility values of 127, 119, and 108 cm² V^-1 s^-1, respectively, which exceed twice that of the films with equal thickness obtained from the conventional solid-phase crystallization approach. A novel film growth mode for fabricating a TCO layer with mobility independent of film thickness is proposed. It is claimed that an appropriate weakly-crystallized as-deposited film is a prerequisite for obtaining favorable crystallites with largely suppressed scattering from grain boundaries, ionized impurities, and film surface. Further, by implementing our 10 nm-thick ICO film into silicon heterojunction architecture, a device efficiency of 25.16% is demonstrated, which is comparable to the reference cell using a 102 nm-thick ICO film. This manifests a 90% indium reduction, indicating significant potential for future optoelectronic applications, particularly for the terawatt-scale photovoltaic industry expansion.

Keywords: cerium‐doped indium oxide (ICO); high mobility; reactive plasma deposition (RPD); ultrathin transparent conductive oxide (TCO).