Acceptor photoconductive polymers

The extension of sensitivity of photoconductive polymers from the UV to the visible range by doping with electron acceptors was reported by Hoegl81 13 Since allknown... 

The situation improved considerably when the active layer was formed by a network of two (donor and acceptor) interpenetrating polymers or small molecules [34,119,121-123,35], For example Buckminsterfullerene C6o mixed with MEH-PPV is very effective in dissociating the exciton created by the incident light. C6o acts as an acceptor and the polymer, as a donor. The transfer of electron from MEH-PPV to fullerene occurs because fullerene has a larger electron affinity. The hole is left at the MEH-PPV because it has small ionization potential. The exciton dissociation results in quenching of the PL by factor up to 104 and in increasing the photoconductivity considerably. The transfer rate... 

These polymers are mainly known for their conductivity, particularly when doped with suitable electron donors or acceptors. Photoconductivity is marginal, and therefore these polymers are of limited interest for the study of this phenomena. Undoped and doped polyacetylene has been studied in some detail [53-57]. Undoped ds-poly-acetylene is photoconductive in UV light [54] doping with AsFs shifts the photoresponse to the visible range, but the polymer also becomes highly dark-conductive. Under certain conditions, the ratio of photo to dark... 

The use of interpenetrating donor-acceptor heterojunctions, such as PPVs/C60 composites, polymer/CdS composites, and interpenetrating polymer networks, substantially improves photoconductivity, and thus the quantum efficiency, of polymer-based photo-voltaics. In these devices, an exciton is photogenerated in the active material, diffuses toward the donor-acceptor interface, and dissociates via charge transfer across the interface. The internal electric field set up by the difference between the electrode energy levels, along with the donor-acceptor morphology, controls the quantum efficiency of the PV cell (Fig. 51). 

Intrinsically carbazole containing polymers are photosensitive in the UV range of spectra. The applications of such polymers in electrophotography and related processes need sensitization to the visual wavelengths. The most acceptable method is charge transfer formation between polymer donor and acceptor molecules. Hoegl pointed out that 0.1-2% of acceptor molecules inserted in the polymer matrix lead to a substantial increase in the photoconductivity especially in the CT bands. Subsequently, a lot of paper were published for CT-carbazole-containing complexes and such materials were used in photosensitive processes. Various types of molecules were used as a photosensitizers. 

Interest in the photoconductive properties of the carbazole nucleus has also prompted studies concerned with its incorporation into condensation polymers. Examples of polymers prepared include polyamides (34), polyesters (35) and polyurethanes (36) (80MI11105). Thorough studies on the CT interactions of these polymers with the monomeric acceptor 2,4,7-trinitrofluorenone have been done. In all cases, the formation constant for the CT complex was higher with polymers than for monomeric models. At least two polymer... 

Le. those which form a charge-transfer complex with the monomer units of the transporting polymer. The charge transfer complex then becomes the carrier generating species and can also contribute to the transport. The electron acceptor can also be chemically attached to the polymer. In such a case the polymer may become intrinsically photoconductive. 

Photoconductivity of polyacenaphthylene was increased dramatically by partial nitration which produced acceptor groups in the polymer The naphthylene groups and the nitrated naphthylene groups apparently formed a charge carrier generating complex. 

---