Semi-transparent Si-rich SixC1−x p–i–n photovoltaic solar cell grown by hydrogen-free PECVD

Abstract

A semi-transparent silicon-rich (Si-rich) silicon carbide (Si_xC_1−x) based thin-film p–i–n junction photovoltaic solar cell is demonstrated, which is synthesized by hydrogen-free plasma enhanced chemical vapor deposition (PECVD) with the conversion efficiency optimized by detuning plasma power and intrinsic layer thickness. The hydrogen-free PECVD process effectively decelerates the decomposition of hydrogen from the Si-rich Si_xC_1−x films so as to facilitate the passivation of surface dangling bonds. When synthesizing at a fluence ratio of R = [CH₄]/[SiH₄]+[CH₄] = 60%, the optical bandgap of Si-rich Si_xC_1−x film is greatly red-shifted to 1.54 eV due to the enhancement of Si content. By reducing the RF plasma power to 20 W, the Si-rich Si_xC_1−x enlarges its above-bandgap (λ= 0.4–0.8 μm) optical absorption up to 10⁴–10⁵ cm⁻¹, which is even one order of magnitude larger than that of bulk crystalline Si. The incomplete dissociation of CH₄ and SiH₄ under low-power PECVD growth also helps to suppress the defects and improve the electrical properties of Si-rich Si_xC_1−x. By doping with the PH₃ and B₂H₆ fluence ratios of 5.8% and 2.1%, the resistivities of n-type and p-type Si-rich Si_xC_1−x films are decreased to 0.87 and 0.12 Ω cm, respectively. Thinning the intrinsic Si-rich Si_xC_1−x layer to 25 nm further promotes the conversion efficiency of the Si-rich Si_xC_1−x based p–i–n photovoltaic solar cell. After annealing at 650 °C, the open-circuit voltage (V_oc) and short-circuit photocurrent density (J_sc) of the annealed Si-rich Si_xC_1−x and amorphous Si based dual-junction thin-film photovoltaic solar cell are increased to 0.78 V and 19.1 mA cm⁻², respectively, leading to a filling factor of 35% and a conversion efficiency of up to 5.24%.