Relationship between collection length and diffusion length in amorphous silicon

We demonstrate a relationship between the diffusion length lD, as measured by the surface photovoltage (SPV) method and the collection length lco, measured on the same thin films of a‐Si:H. lco is the appropriate quantity to describe current collection in p‐i‐n cells of a‐Si:H, which is normally electric‐field dominated. We have shown previously that lco can be used to predict the fill factor of p‐i‐n cells. Therefore, this letter justifies the use of lD measurements by SPV for optimizing the quality of i layers for p‐i‐n cells. An expression for ambipolar diffusion is presented and the experimental results are used to place limits on the relative magnitudes of electron and hole mobilities and lifetimes.