Preparation and Characterization of Quinoxaline-Pyrene-Based Conjugated Copolymers for Organic Photovoltaic Devices

Bakhet A Alqurashy,Imran Ali,Majed Alawad,Ahmed Iraqi,Sulaiman Y Alfaifi,Bader M Altayeb

doi:10.3390/coatings10111098

Abstract

In this study, two novel conjugated polymers, poly(4,5,9,10-tetrakis((2-ethylhexyl)oxy]pyrene-alt-2,3-bis(3-(octyloxy)phenyl)-5,8-di(2-thienyl)-6,7-difluoroquinoxaline) (PPyQxff) and poly(4,5,9,10-tetrakis((2-ethylhexyl)oxy)pyren-alt-2,3-bis(3-(octyloxy)phenyl)-5,8-di(2-thienyl)quinoxaline) (PPyQx), consisting of quinoxaline units with and without fluorine substituents, as electron-accepting moieties and pyrene flanked with dithienyl units as electron-donating moieties were prepared via Stille polymerization reactions for use as electron donor materials in bulk heterojunction (BHJ) solar cells. PPyQxff and PPyQx were characterized by X-ray powder diffraction (XRD), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), cyclic voltammetry (CV), UV−VIS absorption, and nuclear magnetic resonance (NMR) spectroscopy. PPyQxff and PPyQx revealed excellent solution processability in common organic solvents. PPyQxff and PPyQx presented decomposition temperatures above 300 °C. The inclusion of F atoms to the quinoxaline moiety made a slight reduction in the highest occupied molecular orbital (HOMO) level, relative to the unfluorinated polymer, but had no impact on the lowest unoccupied molecular orbital (LUMO) level. PPyQxff and PPyQx exhibited similar physical properties with strong and broad absorbance from 400 to 700 nm and an optical band-gap energy of 1.77 eV. The X-ray powder diffraction study indicated that PPyQxff possessed a reduced π–π stacking distance relative to PPyQx.

Highlights

High request for renewable energy sources to replace fossil fuels has prompted industrial interests and academics attention towards exploring solar energy as an alternative [1]
F atoms. stacking between conjugated backbones. These results clearly show that substitution of the PPyQxff should adopt a further planar structure with enhanced stacking between conjugated polymer backbones. These results clearly show that substitution of the quinoxaline repeat quinoxaline repeat units with fluorine atoms leads to a better packing of polymer chains presumably units with fluorine atoms leads to a better packing of polymer chains presumably through interactions through interactions between polymer chains involving fluorine substituents
Two new narrow band gap donor-acceptor conjugated polymers have been prepared via the Stille coupling reaction

Summary

Introduction

High request for renewable energy sources to replace fossil fuels has prompted industrial interests and academics attention towards exploring solar energy as an alternative [1]. Available photovoltaic technologies are currently dominated by inorganic solar cell technology. These are based on materials including wafer-sized, single junction crystalline silicon. They show relatively high-power conversion efficiency (PCE) (at roughly 25%) [2]. Low-cost production processes, the ease of producing large active panels, high absorption coefficients, ease of fabrication, and light weight constitute key merits in the use of organic semiconductors in this area. OPV devices displayed lower efficiencies relative to inorganic devices; remarkable development of organic semiconductors has been made to boost the PCE and stability of OPV devices to make them a sustainable technology [3,4,5]. Liu et al, reported the highest PCE for organic solar cells (18.22%) [6]

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