Realizing the Potential of RF-Sputtered Hydrogenated Fluorine-Doped Indium Oxide as an Electrode Material for Ultrathin SiO_x/Poly-Si Passivating Contacts

In high-efficiency silicon solar cells featuring carrier-selective passivating contacts based on ultrathin SiO_x/poly-Si, the appropriate implementation of transparent conductive oxide (TCO) layers is of vital importance. Considerable deterioration in passivation quality occurs for thin poly-Si-based devices owing to the sputtering damage during TCO deposition. Curing treatment at temperatures above 350 °C can recover such degradation, whereas the opto-electrical properties of the TCO are affected as well, and the carrier transport at the poly-Si/TCO contact is widely reported to degrade severely in such a procedure. Here, we propose straightforward approaches, post-deposition annealing at 400 °C in nitrogen, hydrogen, or air ambience, are proposed to tailor material properties of high-mobility hydrogenated fluorine-doped indium oxide (IFO:H) film. Structural, morphological, and opto-electrical properties of the IFO:H films are investigated as well as their inherent electron scattering and doping mechanisms. Hydrogen annealing treatment proves to be the most promising strategy. The resulting layer exhibits both optimal opto-electrical properties (carrier density = 1.5 × 10²⁰ cm^–3, electron mobility = 108 cm² V^–1 s^–1, and resistivity = 3.9 × 10^–4 Ω cm) and remarkably low contact resistivities (∼20 mΩ cm² for both n- and p-contacts) in poly-Si solar cells. Even though the presented cells are limited by the metallization step, the obtained IFO:H-base solar cell show an efficiency improvement from 20.1 to 20.6% after specific hydrogen treatment, demonstrating the potential of material manipulation and contact engineering strategy in high-efficiency photovoltaic devices endowed with TCOs.