The p-i-n solar cells with amorphous silicon-alloy had been designed and fabricated in this study. The constant-gap i-a-SiGe:H layer and the composition-graded-gap i-a-SiGe:H layer were used as the main absorption layer respectively. The peak wavelength of the i-SiGe:H absorptance spectrum was around 600 nm which is the irradiance peak wavelength in solar spectrum, while the composition-graded i-a-SiGe:H layer had the higher absorptance for light wavelength ranging from 400 nm to 600 nm. From the experiment results, it could be seen the efficiencies of devices with composition-graded-gap and constant-gap structures were 0.94% and 1.22% respectively, but the device with composition-graded-gap structure had a higher open-circuit voltage (Voc).