Gonev, Hristo Ivov; (2024) Spectroscopic Characterisation of Non-Fullerene Acceptors for Organic Solar Cells. Doctoral thesis (Ph.D), UCL (University College London).

Text Hristo-Ivov-Gonev-PhD-Thesis-Final.pdf - Accepted Version Access restricted to UCL open access staff until 1 July 2025. Download (6MB)

Abstract

The field of organic photovoltaics (OPVs) has achieved significant progress, largely thanks to the advent of non-fullerene acceptors (NFAs), which possess considerably higher absorptivity and tunability compared to fullerene acceptors. This thesis describes three studies into OPV materials, with a particular focus on how using NFAs improves device efficiencies and how to design better acceptors. Investigations are carried out using a number of techniques, including transient absorption spectroscopy, Raman spectroscopy and computational studies. Chapter 3 compares a pair of donor polymers, where one (PBDB) possesses an alkoxy group, while in the other (PBDB-T) that group has been replaced by thiophene. Both fullerene (PC60BM) and non-fullerene (ITIC-Th) blend films are compared. It is discovered that bimolecular recombination of charges via back-electron transfer causes the formation of ITIC-Th triplets in both NFA blends, with PBDB-T:ITIC-Th achieving a larger triplet population than PBDB:ITIC-Th. This increase in triplet yield is attributed to a combination of more efficient hole transfer and faster polymer singlet decay, which create more charges in the PBDB-T system. Chapter 4 presents the NFA FNTz-Teh-FA designed to energetically match with donor polymer P3HT. The P3HT:FNTz-Teh-FA blends exhibits relatively invariant charge carrier decay dynamics across a variety of processing solvents. This invariance is attributed FNTz-Teh-FA’s non-planarity, which enables the NFA to form multiple conformations when blended with P3HT in a film. This creates a dispersive environment independent of the processing solvent and leads to high tolerance to morphological variation. Chapter 5 studies four NFA-like molecules: Fin, OneFin, TwoFin and ThreeFin. TwoFin and ThreeFin are found to have the highest molar absorptivity values. This is attributed to molecular orbital energy level clustering, caused by the localisation of the LUMOs over the region of homoconjugation. The large extinction coefficients suggest that TwoFin and ThreeFin can be further functionalised into NFAs for OPVs.

Download activity - last month

Export as JSONCSVXML

Download activity - last 12 months

Export as CSVXMLJSON

Downloads by country - last 12 months

Export as JSONCSVXML

Archive Staff Only

View Item