Hydrogenated Amorphous Carbon-Silicon Alloys [a-SixC1-x(n):Hy] used as Emitters of Heterojunction Solar Cells

This work focuses on hydrogenated amorphous carbon-silicon alloys [a-Si_xC_1-x(n):H_y] used as emitters of heterojunction solar cells. The a-Si_xC_1-x(n):H_y alloys are deposited on p-type silicon (100) substrates via plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of silane (SiH₄), phosphine (PH₃), methane and hydrogen (CH₄), respectively. For characterization of the heterojunction solar cells, produced as mentioned above, I-V measurements, spectral response and reflection measurements as well as spectroscopic ellipsometry (SE) have been applied. Particularly, we focused on several effects, such as widening of the optical band gap of the emitter within the a-Si_x C_1-x(n):H_y film, the thickness of the emitter and the I-V characteristics of the solar cell. It was confirmed that the band gap EG can be tailored by using an appropriate gas mixture during the decomposition. The optical band gap as well as the thickness of the emitter were determined by spectroscopic ellipsometry. The investigations have shown that the band gap increases with increasing carbon and hydrogen concentration in the feed stock during deposition. Although the addition of carbon (C) degrades the photoelectronic properties in the emitter layer, this deterioration can be minimized by H dilution. We will show that the efficiency of the prepared heterojunction solar cells can be improved with an appropriate addition of carbon and hydrogen in the emitter layer