An ab-initio theoretical description of vibrational, and electronic states, in pristine and doped organic semiconductors.

: (Alternative Format Thesis)

Abstract

This PhD thesis deals with research activity in organic electronics, an extremely exciting field offundamental science, which is complemented by relevant applications in every-day life: optoelectronics,solar energy conversion (photovoltaics), sensing and information technology, just to mentiona few. In this area, charge transfer/energy transfer processes, as well as light matter interaction,play a major role. Within this topic, this work focus on the theoretical study of the electronic structureand related charge transfer/spectroscopic properties of various molecular systems: Coronenecrystals, F4TCNQ/perylene co-crystals, polythiophenes, PCPDT/PCPDT-BT homo- and copolymerbased on thiophene, chemisorbed ferrocene on Si(111) substrate. Particular attention wasdevoted to the calculation of infrared (IR) and electronic spectra associated with the so-called “polaronsignature” in doped organic semiconductors.To assess the reliability and physical meaning of electronic quantities involved in the calculations(like the HOMO/LUMO gap, theoretical spectroscopic intensity and vibrational modes, pursuingthe comparison between neutral and charged systems) a number of different levels of the theoryhave been systematically varied from HF (Hartree-Fock) to “pure” DFT (Density Functional Theory),as well as hybrid B3LYP (Becke 3-Parameter (Exchange), Lee, Yang and Parr 1,2) and longrange corrected Coulomb-Attenuating Method (CAM-B3LYP) functionals. In the attempt to untanglethe physics underlying the polaron formation in charged molecular systems (as evidenced by theoccurrence of giant intensity bands found in IR spectra), the mapping of the vibrational mode betweenneutral and charged systems has been calculated. A major achievement in this work is thatthe vibrational (giant) mode associated with the “polaron” emerges as a new mode (peculiar of thecharged state) not related to any mode existing in the neutral system.

Date of Award	22 Aug 2017
Original language	English
Awarding Institution	University of Bath
Supervisor	Enrico Da Como (Supervisor)