Composites of Double-Walled Carbon Nanotubes with bis-Quaterthiophene-Fluorenone Conjugated Oligomer: Spectroelectrochemical and Photovoltaic Properties.

Overview & Synopsis

A new composite consisting of a semiconducting oligomer, namely 2,7-bis-(3,3′′′-didodecyl-[2,2′,5′,2′′;5′′,2′′′]quaterthiophen-5-yl)-fluoren-9-one (QTF12), and double wall carbon nanotubes (DWCNT) has been prepared in view of its application as an active component in bulk heterojunction photovoltaic cells. Raman spectroelectrochemical investigations show that the onset of the oxidative doping of QTF12 in the presence of DWCNT occurs at E ) 0.475 V vs Ag/Ag+, that is, by 50 mV lower than in the case of pure QTF12. This effect was independently confirmed by UV-vis-NIR spectroelectrochemistry. The lowering of the oxidative doping potential, detected by spectroelectrochemistry, can be taken as a spectroscopic evidence of oligomer-nanotube interactions which result in raising, by 0.05 eV, the HOMO level of these QTF12 molecules which are at the interface with DWCNT. Bulk heterojunction test photovoltaic cells consisting of a ternary system (QTF12-DWCNT, PCBM) show the open circuit voltage (Voc) ) 0.53 V and the power conversion efficiency of 0.43%.