P-i-n type hydrogenated amorphous silicon (a-Si:H) solar cells were deposited by the radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) process at a low substrate temperature of 125 degrees C, which is compatible with low-cost poly (ethylene terephthalate) (PET) plastic substrates. Wide band gap (E(opt) > 1.88 eV) intrinsic a-Si:H films were achieved before the onset of the microcrystalline regime by changing the hydrogen dilution ratios. On the other hand, the structural, optical and electrical properties of p-type hydrogenated amorphous silicon carbide (p-a-SiC:H) window layers have been optimized at 125 degrees C. High quality p-a-SiC:H film with high optical band gap (E(04) = 2.02 eV) and high conductivity (sigma(d) = 1.0 x 10(-7) S/cm) was deposited at 'low-power regime' under low silane flow rates and high H(2) dilution conditions. With the combination of wide band gap p-a-SiC:H window layers and intrinsic a-Si:H layers, a high V(oc) of 1.01 V (efficiency = 5.51%, FF = 0.72, J(sc) = 7.58 mA/cm(2)) was obtained for single junction a-Si:H p-i-n solar cell at a low temperature of 125 degrees C. Finally, flexible a-Si:H solar cell on PET substrate with efficiency of 4.60% (V(oc) = 0.98 V, FF = 0.69, J(sc) = 6.82 mA/cm(2)) was obtained. (C) 2011 Elsevier B.V. All rights reserved.