Time‐resolved photoconductivity measurements with subnanosecond time resolution are applied to study the electric field profile in amorphous silicon solar cells in the range from 0.3 V forward to 0.8 V reverse bias. The method is used for a comparison of state‐of‐the art devices with different junction design. Optical and electrical contributions to the device performance are discussed and the limitations in improving the performance by use ofa‐SiC:H window layers are pointed out.