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Analysis of boron doped hydrogenated amorphous silicon carbide thin film for silicon heterojunction solar cells

Salimi, Arghavan
Silicon based solar cells are the dominant type of solar cells in the photovoltaic industry. Recently, there have been increasing efforts to develop c-Si solar cells with higher efficiency and lower cost. Among them, silicon heterojunction solar cell (SHJ) is attracting much attention because of its superior performance values demonstrated at both R&D and industrial levels. One of the common limiting criteria is the recombination at the front side which can be solved by providing proper passivation at the front contact. In case of amorphous silicon (a-Si), the parasitic absorption of photons and recombination of the minority ca rriers are considerably high, thus, one approach can be increasing its optical band gap to overcome these impediments. One way to increase the optical band gap of a-Si is adding carbon(C) during boron(B) doping and hydrogenating amorphous silicon (a-Si:H). Generally, the p-type a-Si:H optical band gap is around 1.6 eV which is close to the intrinsic a-Si:H optical band gap. Meanwhile, C alloying allows us to increase the optical band gap from 1.6 up to 2.4 eV. In this work, we tried to increase the optical band gap of B doped a-Si:H deposited by PECVD through introducing C into the structure. We modified the deposition parameters such as deposition temperature, RF power of PECVD, and precursors gas flow rates to see their effects on the doping, a-Si:H optical band gap, and amount of C introduced into the structure. The best characteristic parameters that we have achieved for p-a-SiC:H is optical band gap of 1.89 eV with dark conductivity of 1.8×10-5 (Ω.cm)-1. By increasing the RF -power, we have observed that the methane molecules decompose better and C atom incorporates into the structure. Also, increasing the methane flow rate improved the C incorporation within the structure.