In contrast to silicon-based p-n junction photovoltaic solar cells (PVSCs), a silicon rich silicon carbide (SixC1-x)-based thin-film PVSC with enhanced absorption at the visible wavelength region. The silicon rich SixC1-x films are synthesized by using a low-substrate temperature and low-power plasma-enhanced chemical vapor (PECVD) system in a silane-rich environment. The molar ratio of the silicon atoms in SixC1-x grown at 500°C was tunable from 0.63 to 0.66 when reducing RF plasma power from 100 to 20 W. The low-plasma PECVD growth gave the SixC1-x an enhanced broadband absorption at 400–600 nm, where the highest optical absorption coefficient was 1.3 × 105 cm−1. The silicon rich composition also reduced the optical bandgap energy from 2.05 to 1.49 eV. This type of red-shifted cutoff wavelength promoted solar energy conversion at the near-infrared region. Consequently, an ITO/p-SixC1-x/n-SixC1-x/Al PVSC with a silicon molar ratio of 66% enhanced its conversion efficiency from 5 × 10−3 to 4.7% when the n-type SixC1-x thickness was reduced from 150 to 25 nm, which is attributed to the reduced series resistance to 0.6 Ω and the increased shunt resistance to 1500 Ω.
The co-precipitation of Si and SiC quantum dots (QDs) in Si-rich silicon carbide (Si-rich SiC) films with n-type and p-type dopants is preliminarily demonstrated with low-temperature plasma enhanced chemical vapor deposition and high-temperature annealing. With specific hydrogen-free recipe of argon diluted silane (SiH4) and pure methane (CH4), the composition ratio x of Si-rich SixC1-x film can be varied from 0.74 to 0.67 by tuning the flow rate of g = [CH4]/([CH4]+[SiH4]) from 40% to 60%. Both SiC-QDs and Si-QDs can only be precipitated by annealing the Si-rich Si0.69C0.31 grown with g = 50% at 1050°C. The Si0.69C0.31 transfers into a nano-crystallized matrix with buried SiC-QDs and Si-QDs at diameters of 2.5 nm and 4.5 nm, respectively. The co-precipitated SiC-QDs and Si-QDs in Si-rich Si0.69C0.31 shrink the linewidth of c-Si related Raman scattering peak at 520 cm−1 from 87 cm−1 to 42 cm−1, and up-shift the Si-C transverse optical (TO) and longitudinal optic (LO) mode related Raman scattering peaks to 796 cm−1 and 970 cm−1, respectively. Decreasing the flow rate from g = 60% to g = 50% improves the conductivity of Si-rich SixC1-x film by more than one order of magnitude. At optimized recipe of g = 50%, the resistivities of p-type and n-type SixC1-x films are reduced to 2 × 101 Ω-cm and 3.1 × 10−1 Ω-cm, respectively.
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