Influence of the 2,5-bis(pentadecyloxy)terephthalic acid self-assembly layer on the structure and charge transfer properties of poly(p-phenylene vinylene) for application in organic solar cells

Abstract

Composites of poly(p-phenylene vinylene) and self-assembling 2,5-bis(pentadecyloxy)terephtalic acid (PPV/PDTPA) have been deposited on the surface of an ITO glass substrate and tested as a photoactive material for solar energy conversion. Both the morphology, and the electrochemical and photochemical properties of the fabricated composites have been investigated. By carefully controlling the conditions of composite formation, the homogeneous material structure was obtained in which the self-assembling layer of PDTPA forces ordering of PPV chains. Theoretical calculations have indicated that van der Waals forces and hydrogen bonds with a small contribution of π–π stacking interaction between two components are responsible for the composite structure. The voltammetric measurements reveal a 0.11 eV decrease in the band gap energy in comparison to pristine PPV. Additionally, the distribution of energy levels in PDTPA relative to the PPV energy bands also allows charge exchange between the components, favoring charge separation. Therefore, a notable improvement in the operating parameters of a solar cell containing PPV/PDTPA as a photoactive material was observed compared to a cell based on pristine PPV. A power conversion efficiency of 2.66% was attained for organic solar cells based on the PPV/PDTPA composite.