Ge quantum dots (QDs) have been applied to increase the internal quantum efficiency (IQE) of a photodetector up to 1500% at 400 nm and are expected to benefit the performance of solar cells. Ge QDs have been successfully prepared on silicon-based solar cells using plasma enhanced chemical vapor deposition (PECVD) at temperature lower than 300 degrees C. By adjusting the deposition time, RF power and H-2-plasma treatment time, the Ge QDs are optimized for obtaining the highest solar cell efficiency. It is found that the quantum efficiency of the solar cells has been significantly improved by the presence of Ge QDs, particularly in the long wavelength range ( > 600 nm). As a result, the short-circuit current density (Jsc) is increased by 3.3%, and, consequently, the solar cell efficiency is increased.