The Synthesis and Examination of Bridged Oligothiophenes as Small-molecule Semiconductors in Organic Photovoltaic Devices
Dr. Peter Skabara and Dr. Neil Findlay
Organic photovoltaic devices (OPVs) have been a centerpiece of solar power research due to their low-cost fabrication and minimal environmental impact. Recent advancements in synthetic chemistry have enabled the tuning of organic semiconductor functionality at the molecular level, thereby enhancing device specificity and increasing OPV efficiency to levels approaching those required for commercial success. Specifically, oligothiophenes have been widely studied and demonstrate viability as charge transport materials in OPVs. The present study reports the synthesis of a novel family of bridged oligothiophenes with methyl-capped terthiophene, quinquithiophene, and septithiophene backbones for application in OPV devices. The structures were studied with UV-Vis spectroscopy, cyclic voltammetry, and tested for OPV performance in bulk heterojunction solar cells. Successful photocurrent generation was observed for devices fabricated with a donor-acceptor mixture of the terthiophene analogue and PC70BM. A ten-fold increase in power conversion efficiency was attained through the optimization of solution-processing parameters. Meanwhile, the septithiophenebackboned analogue exhibited more desirable optical and electrochemical properties than its terthiophene and quinquithiophene counterparts. However, its tendency to aggregate resulted in non-uniform film morphology, impeded charge transport, and prevented successful photocurrent generation. Improvements in the processability of bridged oligothiophenes are needed to best exploit the properties of these unique organic semiconductors.
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