Hydrogenated amorphous silicon germanium (a-SiGe:H) thin films were prepared by a 13.56-MHz plasma-enhanced chemical vapor deposition (PECVD) method. The optical, optoelectronic, and microstructure properties of the a-SiGe:H thin films prepared with different plasma powers were investigated systematically by transmission, photo/dark conductivity, Raman, and Fourier transform infrared (FTIR) spectroscopy measurements. It was found that when the deposition pressure was high and the hydrogen (H2) dilution ratio ([H2]/([SiH4] + [GeH4])) was low, an appropriate high plasma power could enlarge the optical bandgap (Eg) by reducing the Ge content in the thin film, enhance the film photosensitivity by improving the film microstructure, and increase the film growth rate. As a demonstration, excellent a-SiGe:H thin film with Eg of 1.5 eV, the photosensitivity of above 104 and a growth rate of 6.6 Å s−1 was successfully fabricated for the solar-cell application with a plasma power density of 400 mW cm−2, a deposition pressure of 3 Torr, and a H2 dilution ratio equal to 3 at 220 °C. The underlying mechanism was further analyzed.