Abstract
Abstract Thin-film solar cells are fabricated by low-cost production processes, and deposited on low-cost substrate like glass, stainless steel or plastics. Therefore, thin-film solar cells are an alternative to conventionally used wafer solar cells based on crystalline silicon. The hydrogenated microcrystalline silicon(c-Si:H) thin film solar cells have better absorption efficiency at near infrared and better resistance to degradation caused by sunlight illumination. The purpose of this thesis is develop process for c-Si:H thin films by In-line plasma enhanced chemical vapor deposition(In-line PECVD). When in the process, optical emission spectroscopy(OES) be employed to monitor the stability of plasma and to build the relationship between plasma spectrum and process parameters such as RF power, gas pressure and silane concentration. Correlation among plasma reactive species, process parameters and thin film are established by analyzing material property of thin film and electric property. In addition to SiH* (412.8 nm), the H (656.2 nm), the H (486.2 nm) and the H2 Fulcher (600-630 nm), we also interest in Si* (288 nm) and use OES-ratio(Si*/SiH*, H/Si*H/Si*) to analyze connection between electron temperature and process parameter. We also compared new OES-ratio(Si*/SiH*, H/Si*H/Si*) with OES-ratio(H/H to understand the reaction mechanism of plasma further. H2 fulcher is used to represent the trend of electron density. c-Si:H thin films are prepared by the silane-hydrogen plasma with VHF-PECVD (40.68 MHz). The experiment results found that whether it is varying the silane concentration, RF power or gas pressure, the XC and OES-ratio(H/SiH*, H/SiH*) have the same trend, but the trend of photosensitivity is opposite except for RF power. In the part of electron temperature, OES-ratio(HH, Si*/SiH*) increase with RF power. They also increase with pressure but that are not consistent with the simulation results. But when we replaced OES-ratio(HH, Si*/SiH*) with OES-ratio(H/Si*, H/Si*), the trends of OES-ratio(H/Si*, H/Si*) are consistent with simulation result. The intensity of plasma characteristic species and electron density have the same trend. When the RF power increases, the emission intensity of plasma species get higher as a result of the increases of electron density. But when the gas pressure increases, the intensity of plasma species get lower as a result of the decreases of electron density.. For the different silane concentration, electron density has irregular trend when the silane concentration increase. In the part of electron temperature, there is opposite trend between OES-ratio(HH) and OES-ratio(Si*/SiH*). The trend of OES-ratio(H/Si*) and OES-ratio(H/Si*) are also different depend on variation of silane concentration. Among of them, OES-ratio(H/Si*) has irregular trend, too. Currently, In-line PECVD can deposit c-Si:H thin film which XC = 42% and photosensitivity = 8.74 × 102 at high power(1000 W), high pressure(5 torr) and high silane concentration(3.3%). But the cell efficiency is just 0.01%. Therefore we use lower RF power to reduce the defect at junction between Barrier-layer and I-layer by reduced ion bombardment. When the RF power lower to 600 W, gas pressure at 4 torr, the cell efficiency has been improved dramatically to 4.05%. If the N-I-P layer all deposited in In-line PECVD, we expect the cell efficiency will be improved more.