Hole photogeneration in poly(<i>N</i>-vinylcarbazole)

Abstract

The photogeneration of holes in poly(N-vinylcarbazole) has been investigated as a function of applied electric field, wavelength, and temperature. For fields above 3.0×104 V/cm, the field and temperature dependences of the photogeneration efficiency are in good agreement with predictions based on the Onsager theory of geminate recombination. The quantum efficiency can be described by a thermalization distance which varies from 26 to 30 Å as a function of wavelength and a primary quantum yield which varies between 0.20 and 0.03 as a function of temperature. The photogeneration efficiency increases in steps with decreasing wavelength. Transitions occur between the ground state and the first, second, and third excited singlet states. For a given transition, the efficiency is constant and depends only upon the electric field and temperature. The increase in efficiency which occurs with decreasing wavelength can be explained by an increase in the thermalization distance. The primary quantum yield shows an exponential dependence on reciprocal temperature with an activation energy of 0.05 eV. The thermalization distance is independent of temperature and determined only by the excitation wavelength.