Highly Conductive and Broadband Transparent Zr-Doped In2O3 as Front Electrode for Solar Cells

Abstract

Broadband transparent and highly conducting electrodes are key to avoid parasitic absorption and electrical losses in solar cells. Here, we propose zirconium-doped indium oxide (IO:Zr) as a transparent electrode intrinsically meeting both requirements and demonstrate its application as the front electrode in silicon heterojunction (SHJ) solar cells. The exceptional properties of this material rely on the combination of high-doping and high electron mobilities, achieving with this a wide optical band gap (3.5–4 eV), low free carrier absorption, and high lateral conductivity. A single film of IO:Zr has an electron mobility of 100 cm2/Vcs with a carrier density of 2.5–3 × 1020 cm–3, resulting in a sheet resistance of around 25 Ω/sq for 100-nm-thick films. Their implementation as a front electrode in SHJ solar cells results in an important gain in current density as compared to the standardly used Sn-doped indium oxide. This is due to reduced parasitic absorption in both, the UV and IR, as confirmed by external quantum efficiency measurements. SHJ devices with the optimized IO:Zr front electrode, resulting in current densities of 40 mA/cm2, a fill factor of 80%, and a conversion efficiency of 23.4%.