Determination of localized-state distributions in photoconductive polymers from transient photocurrents measured with the time-of-flight method

Abstract

The applicability of a method for the determination of localized-state distributions in disordered semiconductors to time-of-flight (TOF) photocurrent transients has been numerically examined. The method based on the analysis of the transient photocurrent using Laplace transform has been originally proposed for transient photoconductivity in the materials [H. Naito et al., Appl. Phys. Lett. 64, 1830 (1994)]. It is found that the method correctly works in case of TOF photocurrent transients as well. The improvement of the energy resolution of the method is shown to be possible using the Tikhonov regularization. The method is applied to the analysis of TOF photocurrent transients of poly (phenylene vinylene) (PPV) and poly (methylphenylsilane) (PMPS) thin films, which are promising materials as visible and ultraviolet light emitting diodes (LED), respectively. The results are compared with those of space-charge-limited-current measurements in PPV and PMPS LED's.