24.92% efficient crystalline silicon heterojunction solar cells with Ga-doped ZnO transparent conductive oxide films by RPD

The high cost of indium has driven the development of indium-free alternatives to conventional transparent conductive oxides (TCOs) for crystalline silicon heterojunction (HJT) solar cells. Ga-doped ZnO (GZO) films were deposited at room temperature by reactive plasma deposition (RPD), and their structural, electrical and optical properties were linked to the plasma-state evolution monitored in situ by optical emission spectroscopy (OES). The appropriate oxygen content improved film stoichiometry, c-axis-oriented crystallization and Hall mobility. Among all investigated oxygen contents, the GZO film deposited at 10% oxygen showed the best balance between transparency, carrier transport and device compatibility, with a minimum resistivity of 4.902 × 10 −4 Ω cm and an average optical transmittance of 83.45% in the 400–1100 nm range. When applied as bifacial TCO layers in HJT solar cells with screen-printed 30 wt% Ag-coated Cu electrodes, a power conversion efficiency of 24.92% was obtained. This study provides practical guidance for industrially scalable indium-free transparent electrodes for high-efficiency HJT solar cells.