| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 101 === IV
Abstract
In this thesis, factors affecting the electronic energy levels and optical
absorptions of poly(3-hexylthiophene) (P3HT) are systematically studied,
including the coplanality, the introduction of fused ring on the P3HT main chain
and the strong electron withdrawing cyano (-CN) side group. All the polymers
are synthesized via Stille coupling to afford reasonably high molecular weight (>
10,000) and good solubility in common organic solvent at room temperature.
Considering the effect of coplanality, P3HT with various head-to-tail (HT)
percentages in the main chain ranging from 50% to 98% are synthesized with
regularly distribution of the twists (head-to-head, HH, configurations). The
optical band gap and the electrochemical band gap are in good agreement,
increasing with the decrement of the coplanality. The widen bad gaps are
attributed to the elevated lowest unoccupied molecular oribital (LUMO) and the
lifts are not proportional to the increment in the HH percentages. A small
amount of twists in the main chain would significantly elevate the LUMO by
0.2~0.4 eV, along with the suppression of π-π stacking in the spin-coated thin
film.
Regarding the effect of fused ring in the main chain, cyclopentadithiophene
(CPT) is introduced to the P3HT main chain and the resulting copolymers
containing CPT and 3HT exhibited energy levels similar to those of regioregular
P3HT(rr-P3HT), suggesting the fused ring in the main chain has no effect on the
electronic band structure. However, the strong coplanality of CPT enables the
formation of aggregations of CPT based copolymers in solution at room
temperature. In comparison with rr-P3HT in solid state, the introduction of CPT
would not promote the red absorption; in addition, the π-π stacking is inhibited. The employment of strong electron withdrawing CN side groups
simultaneous lower both the highest occupied molecular oribital (HOMO) and
LUMO by 0.2eV without significantly altering the optical absorption and the
molecular packing in thin films.
|
|---|
