Design, synthesis and applications of novel heterocycle for organic photovoltaic solar cells

Hemlata, P 2015, Design, synthesis and applications of novel heterocycle for organic photovoltaic solar cells, Doctor of Philosophy (PhD), Applied Science, RMIT University.


Document type: Thesis
Collection: Theses

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Title Design, synthesis and applications of novel heterocycle for organic photovoltaic solar cells
Author(s) Hemlata, P
Year 2015
Abstract In this thesis, I have used D-A-D and D-A strategies in design, and synthesized followed by characterized and applied for solution processable photovoltaic devices.

The solution-processable electron acceptor (DPP1) based on fluorene and diketopyrrolopyrrole conjugated moieties was designed, synthesized and characterized completely. DPP1 revealed excellent solubility and high thermal stability which are vital for easy processing. Upon using DPP1 acceptor with the classical electron donor poly (3-hexylthiophene), solution processable bulk-heterojunction solar cells afforded a high open-circuit voltage. A value of open circuit voltage is one of the highest values reported so far for a bulk-heterojunction device using DPP1 non-fullerene acceptor.

The materials which were designed, synthesized, characterized and tested for bulk heterojunction solar cells indicated that there relationship between the three fragments (donor- spacer-acceptor) of a donor-acceptor (D-A) design. Also interested to the design and advancement of new chromopheres based on donor-acceptor-donor (D-A-D) module and push-pull chromopheres used. Naphthalene diimide (NDI), current research interested because of its interesting physical and electronic properties. A potential advantage of naphthalene diimide (NDI) accepting unit is its amenability to incorporate alkyl chains on the nitrogen atoms. The target materials solubility enhance because of these alkyl chain and also excellent film formation without crystallization. To generate new push-pull chromophers, first time NDI has been used in conjugation with triphenylamine (TPA) and benzothiophene (BT) donor functionality based on a D-A-D module that has been fabricated in solution processable inverted bulk heterojunction (BHJ) devices.

Similar observation was found in development of small molecular chromopheres for BHJ. Diketopyrrolopyrrol (DPP) building blocks were reported as a potential electron deficient fragment for the development of non-fullerene acceptor chromopheres and NDI unit has interesting physical and electronic properties. Due to these reasons, new non-fullerene electron acceptors based on NDI and DPP functionalities investigated, where NDI was chosen as the central core with DPP terminal units. It has been applied solution-processable BHJ device along with the classic electron donor, poly (3-hexythiophene) (P3HT). NDI and DPP unit exhibited excellent thermal stability, broad absorption and appropriate energy levels matching with P3HT.

Two-novel solution processable small organic molecules were successfully designed, synthesized and characterized based on a D-A-D structural motif with a common electron accepting moiety, isoindigo with different electron donating functionalities triphenylamine and carbazole respectively. Carbazole analogue compared with triphenylamine (TPA) donor functionality, TPA resulted in an enhanced intramolecular Charge transfer transition and reduction of optical band gap. TPA and carbazole were designed to donor components excellent solubility in common organic solvents, thermal stability and their promising optoelectronics properties encourage to charge-carrier motilities using solution-processable organic field effective transistors.

Overall this study provides an examination of the effect of changing the donor central bridge and acceptor part of the donor-acceptor-donor (D-A-D) modular material for the BHJ solar cells. It is interesting to see how the donor and acceptor modifications in a given D-A module may affect the performance of these materials used for BHJ solar cells.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Applied Science
Keyword(s) Solar cell
Small molecules
Solution-processosable
Bulk-heterojunction
Naphthalenediimiei
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Created: Fri, 23 Oct 2015, 08:49:30 EST by Denise Paciocco
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