Optical and electrochemical study of discrete supramolecular complexes for organic photovoltaic application

Abstract

Supramolecular complex formation using donor and acceptor macrocycles are important field of research in solar energy harvesting. In this study, multiwalled carbon nanotubes is used as an acceptor and its associative interactions with macrocyclic and polymeric donors such as phthalocyanines (free base H2 and Mn centred) and Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) were studied using absorption and emission spectroscopy, electrochemical methods and transmission electron microscopy. The calculated molar extinction coefficients and fluorescence quantum yield values show that the selected donors not only strongly absorb at high wavelengths but also at lower concentrations they effectively release excited state charge at 600 nm (for phthalocyanines) and 624 nm (for polymeric donor). This is further corroborated by the binding constants obtained during this study. The binding constants as calculated from the spectroscopic methods (ranging from 103 to 106 for the macrocycles to polymer) with that of electrochemical methods indicated a similar trend. This was further validated by the low-resolution TEM studies which indicated the decoration of MWCNT with the donors used. Thus, MnPc and PCPDTBT were the most stable of the complexes showing a good promise to find application as active materials in organic photovoltaics.