Variable-Band-Gap Poly(arylene ethynylene) Conjugated Polyelectrolytes Adsorbed on Nanocrystalline TiO₂: Photocurrent Efficiency as a Function of the Band Gap

Abstract

A series of poly(arylene ethynylene) conjugated polyelectrolytes (CPEs) substituted with carboxylic acid side groups have been synthesized and characterized. The polymers feature a backbone consisting of a carboxylated dialkoxyphenylene-1,4-ethynylene unit alternating with a second arylene ethynylene moiety of variable electron demand. The HOMO-LUMO gap is varied across the series, giving rise to a set of four polymers that have absorption maxima ranging from 404 to 495 nm. The CPEs adsorb effectively from solution onto nanostructured TiO(2) films, giving rise to TiO(2)/CPE films that absorb approximately 90% of the incident light at the absorption band maximum. The photocurrent generation efficiency of the TiO(2)/CPE films was examined in a solar cell configuration using an I(3)(-)/I(-) propylene carbonate electrolyte and a Pt/fluorine-doped tin oxide counter electrode. Most of the films exhibit good photocurrent generation efficiency with a peak quantum efficiency of approximately 50% at wavelengths corresponding to the polymers' absorption band maximum. Interestingly, the photocurrent generation efficiency for the lowest-band-gap polymer is substantially lower compared to the other three systems. This effect is attributed to efficient nonradiative decay of excitons at trap sites arising from interchain contacts distal from the TiO(2)/CPE interface.

Photosensitization of Single-Crystal ZnO by a Conjugated Polyelectrolyte Designed to Avoid Aggregation

“…5,6 For example, previous studies suggest that exciton transport to the polymer−semiconductor interface is inefficient when the adsorbed polymers exist as large multichain aggregates, resulting in reduced absorbed photon to current efficiencies (APCE). 7,8 The inefficient transport is believed to arise due to exciton trapping by the interchain aggregate states. 9,10 Clear analogies exist with bulk heterojunction materials, where charge separation and transport are correlated with the aggregation state of the conjugated polymer.…”

Design and Synthesis of Conjugated Polyelectrolytes

“…Copolymerization between 77 and 78 under the Sonagashira reaction conditions yielded the neutral precursor P93, which underwent hydrolysis to give P94. Copolymerization between 77 and other diacetylene monomers followed by base treatment yielded the alternating carboxylated poly(phenylene ethynylene)s P95-P97 [53,117].…”

Phage PVP-SE1 as Tool Recognition in Polydiacetylene to Produce Intelligent Packaging

“…Biosensors have been intensively studied to fulfil this necessity and could be defined as analytical tools that identify and quantify desired target substances from unknown samples [2]. One compound that has been used as a biosensor is the polydiacetylene (PDA), a polymer which has capability to cause modifications in intramolecular conformation and intermolecular packaging, resulting in changes in absorption, fluorescence, and conductive properties of this polymer [2][3][4][5][6].…”