Indacenodithiophenes as n-type semiconductors for organic solar cells

Gottardi, Cosma E.A. (2020) Indacenodithiophenes as n-type semiconductors for organic solar cells. PhD thesis, University of Glasgow.

Abstract

In an effort to advance humanity’s use of renewable energy, fifteen new non-fullerene acceptor materials based on indacenodithiophene have been synthesised, characterised, and initial tests of their application in organic solar cells have been conducted. The highest power conversion efficiencies obtained are above 5%. During the synthetic chemistry portion of this project, a number of further compounds were attempted and some interesting lessons learnt, which are also discussed.

Chapter 1 introduces the field of organic photovoltaics, explaining its relevance today, the basic operating principles, and the industrial fabrication techniques and their equivalents in the research laboratory. It highlights how current research efforts have been directed away from buckminsterfullerene (C60) and its derivatives as the n-type organic semiconductor of choice. Recent research efforts in the field of non-fullerene n-type semiconductors (NFAs) are then summarised, with a particular focus on molecules containing the indacenodithiophene (IDT) motif.

Six new alkyl-modified derivatives of the literature molecule IEIC are presented in Chapter 2. The preliminary device fabrication results obtained indicate that unbranched alkyl side chains perform better than their branched counterparts, and that alkyl group orientation towards the electron-deficient terminal group can have a beneficial effect on the photocurrent. A best power conversion efficiency of 5.11% is thus obtained under industrially relevant processing conditions. Additionally, the ambiguity in the literature regarding the regioselectivity of the lithiation of 2,5-dibromo-3-alkylthiophene with n-butyllithium is proven to occur in the 5-position through derivatisation of the resulting aldehyde and crystallisation.

In Chapter 3, two different, strongly electron-withdrawing moieties (based on 1,3-bis(diycano-methylidene)indane and tetracyanobutadiene) containing four nitrile groups each are explored for the first time in conjunction with IDT as the electron-rich unit. Five new dyes are thus presented and tested as non-fullerene n-type semiconducting dyes in organic solar cells. Furthermore, a retro-Knoevenagel reaction is demonstrated on silica gel.

Three new dyes are presented in Chapter 4, based on IDT as the central, electron-rich moiety, the cyanovinyl moiety as linkers and substituted benzenes as the terminal groups. The variation in performance of the dyes as n-type materials in organic solar cells is linked to the different substitution on the terminal groups.

The final set of new dyes for organic solar cells are presented in Chapter 5. Here, four dyes, containing two IDT moieties each, are used to systematically investigate the role of the length of the central linker (thiophene or bithiophene) and the influence of the terminal electron-withdrawing group (either fluorinated or non-fluorinated) on solar cell parameters. In conjunction with one of two different p-type materials, one compound achieves a power conversion efficiency of 3.0% based on preliminary device fabrication tests alone.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: The following three institutions are gratefully acknowledged for funding stipend, travel and research costs over 3.5 years: the Energy Technology Partnership (ETP, supported by the Scottish Funding Council), Project No. 143; the University of Glasgow Trust Fund; and Merck Chemicals ltd.
• Keywords: OSC, OPV, IEIC, organic solar cell, organic photovoltaics, NFA, non-fullerene acceptor, small-molecule acceptor, acceptor material, IDT, indacenodithiophene, density functional theory, electrochemistry, bulk heterojunction, dye, functional dye, TCBD, regioisomers, side chain, blade-coating, renewable energy, organic synthesis, materials science.
• Subjects: Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Supervisor's Name: Cooke, Professor Graeme
• Date of Award: 2020
• Embargo Date: 14 July 2023
• Depositing User: Cosma E A Gottardi
• Unique ID: glathesis:2020-81520
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jul 2020 09:40
• Last Modified: 02 Jun 2021 16:15
• URI: https://theses.gla.ac.uk/id/eprint/81520