Rectification effects based on the <i>p</i>-<i>n</i> junction of poly[γ- (β-<i>N</i>-carbazolylethyl) -<i>L</i>-glutamate]— 2,4,7-trinitrofluorenone systems

Abstract

In the dark and under illumination, it has been found that rectification effects in an organic photoconductor system are attributable to a p-n junction barrier. This junction was accomplished by a doping process similar to one used in inorganic semiconductors. The p-n junction barrier was made by immersing a poly[γ- (β-N-carbazolylethyl) -L-glutamate] (PCLG) film in either benzene or a methylethylketone solution of 2,4,7-trinitrofluorenone (TNF), since both benzene and methylethylketone are poor solvents for PCLG and are suitable solvents for TNF. PCLG and PCLG doped with TNF behave as p-type and n-type organic semiconductors, respectively, and a p-n junction with a continuous interface can be accomplished in the sandwich structure system of In2O3//PCLG/PCLG-TNF complex//Au. In this sample, rectification effects both in the dark and under illumination have been observed to be in good agreement with a theoretical equation of the p-n junction for inorganic semiconductors. However, the potential drop across the p-n junction barrier is depressed, being much smaller than the voltage applied externally to the photocell because of the remarkably high electrical resistivities of PCLG and the PCLG-TNF complex. Furthermore, even without an applied field—that is, with a short circuit—the photovoltaic current has been observed and attributed to the junction barrier. On the other hand, in the In2O3//PCLG//Au and In2O3//PCLG-TNF complex//Au systems it has been found that neither dark currents nor photocurrents attributable to a p-n junction are observed.