Highly Transparent\nConductive Gallium-Doped Zinc Oxide\nThin Films Grown by Reactive Plasma Deposition for Silicon Heterojunction\nSolar Cells

The\nconsumption of indium (In) is an obstacle for terawatt-scale\nsilicon heterojunction (SHJ) solar cells. To reduce the use of In\nand achieve sustainable development, the development of economical\nand environmentally friendly transparent electrodes has become a critical\nissue. Here, we report crystalline silicon heterojunction solar cells\nwith reactive plasma deposition (RPD) grown ZnO:Ga<sub>2</sub>O<sub>3</sub> (GZO) at room temperature as a transparent conductive oxide\n(TCO) layer. Meanwhile, SHJ solar cells with magnetron sputtered indium\ntin oxide (ITO) transparent conductive layers are compared as reference.\nGZO thin films exhibit good crystallinity with (002) preferred orientation.\nThe optical and electrical properties of GZO thin films with different\ndoping concentrations have been systematically studied. Under the\ncondition of 3.0 wt % doping concentration and 545 nm thickness, the\ncarrier concentration and electron mobility of GZO film reach 2.95\n× 10<sup>20</sup>/cm<sup>3</sup> and 32.56 cm<sup>2</sup>/V·s,\nrespectively; thus, a resistivity of 7.46 × 10<sup>–4</sup> Ω cm is obtained. The average transmittance of the glass/GZO\nfilm is 83.3% in the wavelength range of 400–1200 nm. The contact\nresistance for GZO/n-a-Si:H is calculated to be 48.0 mΩ cm<sup>2</sup>. GZO-SHJ solar cell exhibits a higher minority carrier lifetime\nand thus higher <i>Voc</i> due to less interface damage\nduring thin film deposition. The GZO-TCO film is used in a SHJ solar\ncell, achieving a device efficiency of 21.48%. The results shows that\ngallium doping of GZO increases electrical conductivity and regulates\noxygen vacancies. In-free TCO grown by a low-bombardment RPD technique\nwill contribute to boosting the development of the SHJ solar cell\nphotovoltaic industry.