Figure 4
Schematic illustration of photodoping mechanism in donor-acceptor photoconductor devices.
(a) Device operation under low-intensity irradiation in which both the donor (e.g. P3HT/CdSe NCs/PbS NCs) and acceptor (e.g. C60 nanorods) are able to absorb the incident light. Electron transfer, with a rate 1/τCT, from the donor occurs contributing to the filling of acceptor trap states and increasing the electron mobility of the acceptor. The trapped electron may then recombine with the hole in the donor (with rate 1/τ) returning the electron mobility to its original value. This process leads to an increased charge carrier concentration and facilitates the photoexcited electrons generated in the acceptor to contribute to photocurrent, which in the absence of photodopant get localized in the traps. (b) As the traps are filled, electrons transferred from the donor are also able to contribute to the photocurrent and the electron mobility in the acceptor is further enhanced. (c) Irradiation at wavelengths below the acceptor bandgap results in trap filling only occurring via electron transfer from the photodonor. Transferred electrons may contribute to the photocurrent when trap saturation occurs or via thermalisation (with rate 1/τT) from trap states prior to this. In (a) and (b) recombination of trapped electrons with the hole in the acceptor is also possible.
