Highly Transparent Conductive Gallium-Doped Zinc Oxide Thin Films Grown by Reactive Plasma Deposition for Silicon Heterojunction Solar Cells

The consumption of indium (In) is an obstacle for terawatt-scale silicon heterojunction (SHJ) solar cells. To reduce the use of In and achieve sustainable development, the development of economical and environmentally friendly transparent electrodes has become a critical issue. Here, we report crystalline silicon heterojunction solar cells with reactive plasma deposition (RPD) grown ZnO:Ga₂O₃ (GZO) at room temperature as a transparent conductive oxide (TCO) layer. Meanwhile, SHJ solar cells with magnetron sputtered indium tin oxide (ITO) transparent conductive layers are compared as reference. GZO thin films exhibit good crystallinity with (002) preferred orientation. The optical and electrical properties of GZO thin films with different doping concentrations have been systematically studied. Under the condition of 3.0 wt % doping concentration and 545 nm thickness, the carrier concentration and electron mobility of GZO film reach 2.95 × 10²⁰/cm³ and 32.56 cm²/V·s, respectively; thus, a resistivity of 7.46 × 10^–4 Ω cm is obtained. The average transmittance of the glass/GZO film is 83.3% in the wavelength range of 400–1200 nm. The contact resistance for GZO/n-a-Si:H is calculated to be 48.0 mΩ cm². GZO-SHJ solar cell exhibits a higher minority carrier lifetime and thus higher Voc due to less interface damage during thin film deposition. The GZO-TCO film is used in a SHJ solar cell, achieving a device efficiency of 21.48%. The results shows that gallium doping of GZO increases electrical conductivity and regulates oxygen vacancies. In-free TCO grown by a low-bombardment RPD technique will contribute to boosting the development of the SHJ solar cell photovoltaic industry.