Photoconductivity in Mixed Stack Do nor: Acceptor Crystals: Quasi One-Dimensional Electron Transport in Anthracene: Pyromellitic-dianhydride

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Abstract
Improvements of the purification, material handling, and crystal growth techniques of the mixed stack donor:acceptor complex anthracene:pyromellitic-dianhydride resulted in big, high purity single crystals, which allowed us to measure a full “microscopic” (i.e. non shallow trapping-perturbed) electron mobility tensor and to study the anisotropy of the temperature dependence law of electron transport for the first time for a representative of this class of materials. These experiments reveal that electron transport is strongly anisotropic. The highest electron mobility occurs along the dononacceptor stacking axis c, with an anisotropy of the principal axes mobilities μ33:μ22:μ11 = 256:15.5:5.0 (in units 10−3 cm2/Vs) at T = 330 K, and with temperature dependences μ3 ∼ T −1.4(1), μ22 ∼ T−0.9(1), and μ11 ∼ T −0.0(1). Preliminary results obtained for holes show that hole transport is thermally activated with E act = 0.58 eV in the temperature range between 310 and 440 K for most samples, that anisotropy is small and that the effective hole mobilities are higher for certain directions than the respective microscopic electron mobilities.