# Why is exciton diffusion a problem in organic photovoltaics and not in inorganic photovoltaics?

On page 2 of this paper: "When the incident photon hits electrons at the ground state, inorganic semiconductors generate free carriers. However, in organic semiconductors, excited electrons slightly relax and then form an exciton, a bounded electron and hole pair."

Why is this only applicable to organic semiconductors?

For most semiconductor, e.g. GaAs, a exciton has binding energy about 6 meV ($$0.006 eV$$) and with a binding length about $$200 \dot{A}$$. That is a very loosely binded state, can be broken into free electron and hole, easier to propagate out of the surface region.