Influence of morphological inhomogeneity induced carrier diffusion on transient photocurrent pulse shape in organic thin films

TL;DR

This study uses Monte Carlo simulations to explore how film morphology-induced carrier diffusion affects the shape of transient photocurrent pulses in organic thin films, highlighting the importance of morphology on charge transport measurements.

Contribution

It introduces a detailed simulation analysis of how inhomogeneous film morphology influences photocurrent pulse broadening, emphasizing the role of morphology-induced carrier diffusion.

Findings

In homogeneous films, decreasing energetic disorder reduces pulse broadening.

In inhomogeneous films, pulse broadening initially increases then decreases with disorder reduction.

Morphology significantly impacts the interpretation of transient photocurrent measurements.

Abstract

The influence of film morphology induced carrier diffusion on the broadening of the time-of-flight transient photo-current pulse was investigated using Monte Carlo simulation in organic thin films. Assuming the Gaussian Disorder Model for the charge transport the simulation of the time-of-flight photo-current pulse shape was carried out for homogeneous and inhomogeneous films by varying the overall energetic disorder of the system. In the case of homogeneous system, the value of the tail broadening parameter (W) of the photocurrent pulse is found to decrease upon decreasing the energetic disorder. The observed behavior is explained by using the temporal evolution of carrier diffusion coefficient. In case of the inhomogeneous system, upon decreasing the overall energetic disorder of the system the value of W initially attained a maximum before it started to decrease. This is attributed to the morphology dependent carrier diffusion in the latter case. This study elicits the importance of the influence of the film morphology induced carrier diffusion on the experimentally measured shape of the time-of-flight transient photo-current pulses, which is found to be generally ignored.