Polymorphous silicon-germanium (pm-SiGe:H) thin films with Ge contents varying from I to 35% were fabricated by plasma enhanced chemical vapour deposition in a high pressure range (1350 mtorr) and under high hydrogen dilution. The electrical and optical properties of these films were studied using a set of complementary techniques. These materials were then incorporated in the i layer of p-i-n solar cells. The performance of such solar cells and the use of these pm-SiGe alloys as the bottom cell of tandem pm-Si:H/pm-SiGe:H cells are finally discussed with the help of numerical simulations.