Deposition and Characterization of High-Efficiency Silicon Thin-Film Solar Cells by HF-PECVD and OES Technology

The optical emission spectrometer (OES) is an effective experimental tool for monitoring plasma states and the composition of gases during the growth of silicon thin films by plasma-enhanced chemical vapor deposition. In this paper, hydrogenated amorphous silicon (a-Si) (a-Si:H) and microcrystalline silicon (μc-Si) thin films have been deposited in a parallel-plate radio frequency (RF) plasma reactor using silane and hydrogen gas mixtures. The plasma emission atmosphere was recorded using an OES system during the growth of the Si thin films. The plasma was simultaneously analyzed during the process using an OES method to study the correlation between growth rate and microstructure of the films. In the deposition, the emitted species (SiH*, Si*, and H*) were analyzed. The OES analysis supported a chemisorption-based deposition model of the growth mechanism. The effects of RF power, electron-to-substrate distance, and H₂ dilution of the emission intensities of excited SiH, Si, and H on the growth rate and microstructures of the film were studied. Finally, single-junction a-Si:H and μc-Si solar cells were obtained with initial aperture area efficiencies of 9.71% and 6.36%, respectively. A tandem a-Si/μc-Si cell was also realized with an efficiency of 12.3%.