HOLE PHOTOGENERATION IN BISPHENOL-A-POLYCARBONATE DOPED WITH N-ISOPROPYLCARBAZOLE

The photoionization of holes in a polycarbonate polymer doped with N-isopropylcarbazole (NIPC) has been investigated as a function of electric field, temperature, wavelength, and NIPC concentration. The experimental results are compared to predictions of the Onsager theory, assuming the distribution of electron-hole separation distances are described by δ and simple exponential functions. The results show good agreement with analyses based on the assumption that the charge-pair configurations are described by a δ function. Depending on the NIPC concentration, the photogeneration efficiency can be described by a primary quantum yield between 0.03 and 0.20 and a thermalization distance between 18 and 20 Å. The photogeneration efficiency increases in steps with decreasing wavelength. Discontinuities are observed between the first and second and the second and third excited singlet states. The increase in efficiency with decreasing wavelength is explained by an increase in the thermalization distance, while the increase in efficiency with NIPC concentration is due to the concentration dependence of the primary quantum yield. The thermalization distance is independent of both temperature and NIPC concentration.