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

A semi-transparent silicon-rich (Si-rich) silicon carbide (SixC(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 SixC(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 SixC1-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 SixC1-x enlarges its above-bandgap (lambda = 0.4-0.8 mu m) optical absorption up to 10(4)-10(5) 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 (SiC1-x)-C-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 SixC1-x films are decreased to 0.87 and 0.12 Omega cm, respectively. Thinning the intrinsic Si-rich SixC1-x layer to 25 nm further promotes the conversion efficiency of the Si-rich SixC1-x based p-i-n photovoltaic solar cell. After annealing at 650 degrees C, the open-circuit voltage (Voc) and short-circuit photocurrent density (Jsc) of the annealed Si-rich SixC1-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%.