Preliminary Oral Exam – Moneim Ismail
PhD Student with Sumit Chaudhary
Title: Effect of electric field on the growth of organic electronic thin-films and devices
Abstract: π-Conjugated polymers (π-CPs) have garnered great interest since their discovery. In contrast to inorganic semiconductors, these materials are well known for their semi-crystalline or amorphous nature. Structural disorder in π-CPs, coupled with the insulating alkyl chains – responsible for dissolving the polymer in organic solvents – severely hinder the carrier mobility. To alleviate this problem, we reported on the effect of electric field (E-field) on the structural and optoelectronic properties of solution-processed π-CPs films and devices. In addition to control (C), wet polymer films were subjected to an E-field at three different orientations – horizontal (H), tilted (T) and vertical (V) with respect to the film surface. While grazing incidence wide-angle x-ray scattering (GIWAXS) shows an increased edge-on stacking for the vertically applied E-field, the conductive force microscopy (c-AFM) current maps of the tilted and vertical films manifest highly conductive domains. Furthermore, unipolar hole-only devices and organic field-effect transistors (OFETs) exhibit an enhancement of the mobility by ~144% and ~70% at tilted and horizontal E-field, respectively. Remarkably, organic solar cells (OPVs) recorded 17% power conversion (PCE) enhancement, and organic light-emitting diodes (OLEDs) achieved a 460% increase in the electroluminescence efficiency (ELη). The advantage of our approach lies in its universality and simplicity, and in capability for anisotropic control of morphology and properties, tailorable for different families of organic electronic devices.