Photogeneration in Trinitrofluorenone-Poly(N-Vinylcarbazole)

Experimental results for the field dependence of the photogeneration efficiency are interpreted in terms of a two step process. The first step involves autionization of the photon-excited bound state into a continuum state, and has efficiency φ0. The second step depends strongly on the applied field and involves separation of the electron-hole pair by diffusion under the influence of their mutual Coulomb attraction and the applied field. The photogeneration efficiency for the system 0.06 mole 2,4,7-trinitro-9-fluorenone to 1 mole of the poly (N-vinylcarbazole) monomer has been determined in the field range from 104 to 5×105 V/cm for temperatures from 4 to 50°C. The experimental results are compared to the predictions of the Onsager theory of geminate recombination, which is thought to describe the second step in the process. The field dependence of the photogeneration efficiency is used to determine that the yield into the auto-ionized state φ0 is approximately 0.23, and the initial electron-hole separation r0 is 25 Å. The increase in photogeneration efficiency observed upon increasing the trinitrofluorenone content is attributed to an increase in r0 rather than φ0, but it is the high φ0 for this system which results in higher intrinsic photogeneration efficiency than that of anthracene.