High-Mobility Hydrogenated Fluorine-Doped Indium Oxide Film for Passivating Contacts c-Si Solar Cells

Broadband transparent conductive oxide layers with high electron mobility (μ_e) are essential to further enhance crystalline silicon (c-Si) solar cell performances. Although metallic cation-doped In₂O₃ thin films with high μ_e (>60 cm² V^-1 s^-1) have been extensively investigated, the research regarding anion doping is still under development. In particular, fluorine-doped indium oxide (IFO) shows promising optoelectrical properties; however, they have not been tested on c-Si solar cells with passivating contacts. Here, we investigate the properties of hydrogenated IFO (IFO:H) films processed at low substrate temperature and power density by varying the water vapor pressure during deposition. The optimized IFO:H shows a remarkably high μ_e of 87 cm² V^-1 s^-1, a carrier density of 1.2 × 10²⁰ cm^-3, and resistivity of 6.2 × 10^-4 Ω cm. Then, we analyzed the compositional, structural, and optoelectrical properties of the optimal IFO:H film. The high quality of the layer was confirmed by the low Urbach energy of 197 meV, compared to 444 meV obtained on the reference indium tin oxide. We implemented IFO:H into different front/back-contacted solar cells with passivating contacts processed at high and low temperatures, obtaining a significant short-circuit current gain of 1.53 mA cm^-2. The best solar cell shows a conversion efficiency of 21.1%.