High-throughput optimization of near-infrared-transparent Mo-doped In2O3 thin films with high conductivity by combined use of atmospheric-pressure mist chemical-vapor deposition and sputtering

Publication date: 31 March 2017
Source:Thin Solid Films, Volume 626
Author(s): Naoomi Yamada, Masayoshi Yamada, Haruna Toyama, Ryuichiro Ino, Xiang Cao, Yuuki Yamaguchi, Yoshihiko Ninomiya
Thin films of near-infrared (NIR)-transparent and highly conductive Mo-doped In2O3 (IMO) were prepared as transparent electrodes in thin-film photovoltaic cells and energy-efficient windows. The fabrication process was rapidly optimized by the combined use of atmospheric-pressure mist chemical-vapor deposition (mist-CVD) and sputtering. Mist-CVD was used to rapidly deposit IMO thin films with various Mo-dopant concentrations. We obtained highly conductive IMO thin films with transmittance above 70% in a wide wavelength range of 0.3–2.5μm when the Mo-dopant concentration was ~1at% and the Mo dopants had an oxidation state of +4. The IMO films with the optimum Mo-dopant concentration of ~1at% had low resistivities of (3–4)×10⁻⁴ Ωcm resulting from high electron mobilities exceeding 80cm² V⁻¹ s⁻¹and suppressed electron densities of (2–3)×10⁻⁴ cm⁻³, which prevented the degradation of transparency in the NIR region. We applied these findings to the growth of IMO thin films by sputter deposition, which is readily extendable from laboratory scale to industrial scale. As a result, a high-performance IMO film was successfully obtained in only a few deposition runs. The optimized sputtered IMO film exhibited an extraordinarily high electron mobility of 93cm² V⁻¹ s⁻¹ and relatively low electron density of 1.5×10²⁰ cm⁻³, leading to a plasma wavelength that was longer than 4μm. This optimized IMO film allowed passage of the full solar spectrum and exclusively reflected far-infrared light corresponding to thermal radiation at room temperature, allowing it to be used as transparent electrodes in photovoltaic cells and heat-reflective electrodes in energy-efficient electrochromic windows. We believe the combination of mist-CVD and sputtering can be extended to rapid optimization of other functional oxide systems.