Broadband transparent conductive oxide layers with high
electron
mobility (μe) are essential to further
enhance crystalline silicon (c-Si) solar cell performances. Although
metallic cation-doped In2O3 thin films with
high μe (>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 μe 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%.
In high-efficiency silicon solar cells featuring carrierselective 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 × 10 20 cm −3 , electron mobility = 108 cm 2 V −1 s −1 , and resistivity = 3.9 × 10 −4 Ω cm) and remarkably low contact resistivities (∼20 mΩ cm 2 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.
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