Free-carrier photogeneration in electron donor, electron acceptor, and bifunctional molecular glasses

We report free carrier photogeneration yields for an electron-donor, an electron-acceptor, and an electron-donor- acceptor molecular glasses. The donor molecule is 1,1-bis- (tri-p-tolylamine) cyclohexane (TAPC), the acceptor N,N'- bis(1,2-dimethylpropyl)-1,4,5,8-naphthalenetetracarboxylic diimide (NTDI), and the bifunctional molecule N-(p-(di-p- totylamino)phenyl)-N'-(1,2-dimethylpropyl)-1,4,5,8- naphthalenetetracaboxylic diimide (TAND). The functional moiety of TAND is derived from the donor and acceptor molecules. The photogeneration yields are obtained by xerographic photoinduced discharge with a positive bias or a negative bias on the free surface at room temperature. The primary quantum yields and thermalization distances derived from fitting the experimental data to a model due to Onsager are similar for these amorphous materials, suggesting that there is no apparent correlation between the photogeneration of free carriers and their morphology. Action spectra of the free carrier photogeneration of TAND are obtained at a constant field. The spectral range encompasses the localized and charge-transfer-type electronic state transitions. The action spectra show that the free carrier photogeneration is predominately due to the absorption derived from the charge transfer transition and the acceptor moiety, with the latter having higher yields by about a factor of two. An abrupt decrease of the yield in the donor moiety absorption region is also observed. We attribute the drastic change in the spectral response of the photogeneration yield to hole trapping and recombination.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.