A series of low band-gap conjugated polymers with intramolecular charge
transfer properties were synthesized and bulk heterojunction devices based on
these polymers were fabricated. The electrochemical and photophysical properties
of the polymers were tuned by using different electron withdrawing molecules or
ruthenium complexes as the comonomer. Preliminary results suggested that the
electronic structures of the polymer were significantly altered by the incorporation
of different acceptor units. The polymers also demonstrated intense absorption
bands in the visible region, indicating that they are suitable photoactive materials
in bulk heterojunction devices.
The synthesis and characterization of a series of organic donor-acceptor
copolymers were studied. All of the polymers contained alternating
cyclopenta[2,1- b:3,4-b’]dithiophene (CPDT) units. The effects of the different
acceptor monomers were evaluated. The electron-withdrawing carboxylate and
amide functional groups of the acceptors were found to effectively stabilize the
HOMO levels of the polymer, and the optical band-gaps were significantly
reduced. Bulk heterojunction devices were fabricated using the polymers and
6,6-phenyl C61 butyric acid methyl ester (PCBM) as donors and acceptors
respectively. These devices exhibited high open circuit voltage (Voc) up to 0.86 V.
The extended photosensitizing range was confirmed by the external quantum
efficiency (EQE) spectra. The device performance was further improved by
optimizing the active layer thickness and applying 1,8-diiodooctane in the blend
solution.
A new synthetic route to novel ruthenium containing polymers was also
reported. [Ru(L)(L’)Cl2] complexes (L and L’ = bidentate N^N ligands) with a
dibromo-substituted ligand were found to be polymerizable by Stille cross-coupling
reaction. The subsequent displacement of the chloride ligands by
thiocyanate was highly effective and the structures of the target polymers were
fully characterized. The main chain absorption showed a significant red-shift upon
metal coordination and the metal-to-ligand charge transfer (MLCT) of the
complex strengthens the photon harvesting ability of the polymer. The dual
function of these Ru(II) complexes demonstrated a new avenue to develop new
classes of optoelectronic materials. The extent of _-delocalization of the ancillary
ligands also showed interesting effects on the electronic properties of the
polymers. Bulk heterojunction devices were fabricated. Photovoltaic response was
observed in these devices, and the device performance can be improved by further
modifying the surface morphology of the blend films. / published_or_final_version / Chemistry / Master / Master of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/174480 |
| Date | January 2012 |
| Creators | Cheung, Wai-kei., 張偉基. |
| Contributors | Chan, WK |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47753006 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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