Carrier Generation Processes in Poly(N-Vinylcarbazole) Films

Studies on the conductivity and photoconductivity of amorphous films of poly ($N$-vinylcarbazole) with Sn${\mathrm{O}}_2$ and metal electrodes show that the dark conductivity is dominated by the Richardson-Schottky field-assisted hole emission from positively biased metal electrodes, provided the metal work function is greater than 3.8 eV. When the metal electrode is negatively biased or with lower-work-function electrodes, the conductivity appears to be dominated by a bulk-polymer-film effect. The current-voltage characteristics of the latter effect do not support a Poole-Frenkel process. High-work-function metal electrodes in positive bias give rise to hole-photoemission tails in the photocurrent-action spectrum. A photocarrier generation process, which onsets at 1.8-1.9 eV and obscures hole photoemission from low-work-function metal electrodes, produces a linear dependence of photocurrent on light intensity and appears to be associated with electronic transitions in the polymer film.