in general ....summarized as follows
1- Absorption of incident light by active layer is equivalent to electron-hole pair (exciton) creation. The absorption process makes the molecules of material to be in excited state. As a matter of fact, the organic materials absorbs small amount of the incident light that related to energy gaps of semiconductor materials whereas the mostly of these materials have energy gaps not less than 2 (eV) which gave a probability to absorb about 30% of incident light. In addition to other factors like crystallization of the films, temperature of annealing films leading to morphology factor of the film surface and reflection losses which also related to surface of active layer.
2- The generated excitons as result of incident light will be diffused to the donor: acceptor interface (junction) before decay as radiation.
3- The excitons stationed at the donor/acceptor interface will be separated into dissociated charge carriers that mean the electron (hole) at the interface transfer to adjacent acceptor (donor) molecule. This step of carriers transfer is usually exothermic and very fast (~100fs).
4- Dissociated charge carriers will be collected by metals electrodes.
Read through the use of various layers in this structure. Later, draw the band structure of the p-n junction. The band structure will give the idea as to how the excitons separate in two opposite directions.
Here, p-type CdTe or CuS are the light absorbing layers (requires a certain thickness for harnessing maximum solar radiation) and the n-type CdS is called as a window layer, for forming the junction.
Transport is just like any other p-n junction. Granular nature of the semiconductors and the high interface state densities alter the junction and transport characteristics, but basic principle remain.
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