Impact of dithienyl or thienothiophene units on the optoelectronic and photovoltaic properties of benzo[1,2,5]thiadiazole based donor–acceptor copolymers for organic solar cell devices

Andrew J Pearson,David G Lidzey,James Kingsley,Saif A Haque,Darren C Watters,Ahmed Iraqi,Luke X Reynolds,Pier P Marchisio,Mohd S Sarjadi,Hunan Yi

doi:10.1039/c4ra07186g

Andrew J Pearson, David G Lidzey + Show 8 more

Open Access

https://doi.org/10.1039/c4ra07186g

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Journal: RSC Adv.	Publication Date: Jan 1, 2014
Citations: 13	License type: cc-by

Affiliation: University of Sheffield, Imperial College London

Abstract

We report a comparative study on four donor–acceptor benzothiadiazole-based copolymers containing dithienyl or thienothiophene moieties for application in organic photovoltaic (OPV) devices. Bulk-heterojunction OPV devices are fabricated having power conversion efficiencies ranging between 4 and 6%. Morphological, spectroscopic and charge-transport measurements are used to investigate the influence of either the dithienyl or thienothiophene moieties on the structure and photophysical properties of the copolymer and copolymer:PC71BM blend films and rationalise the solar cell characteristics. Although all copolymer:PC71BM blends exhibit comparable hole polaron yields, solar cell devices with the highest power conversion efficiencies are correlated with increased charge-carrier mobility of the copolymer and enhanced aggregation of PC71BM in the blend.

Highlights

Solution-processable photovoltaic devices are a promising technology for low-cost solar energy conversion, with organic photovoltaic devices (OPVs) attracting signi cant attention from a wide range of traditional research elds over the past decade.[1,2,3,4]
Previous studies have shown that the magnitude of DOD provides a reasonable indicator of the quantum yield of dissociated charges, with further reports of this signal correlating with photocurrent generation efficiency in a fabricated OPV device.[33]
In this study two new medium band-gap donor–acceptor copolymers comprising 2,7-carbazole or 2,7- uorene units positioned between thienothiophene and benzothiadiazole units have been synthesised

Summary

Introduction

Solution-processable photovoltaic devices are a promising technology for low-cost solar energy conversion, with organic photovoltaic devices (OPVs) attracting signi cant attention from a wide range of traditional research elds over the past decade.[1,2,3,4] OPV devices that employ blends of conjugated polymers and fullerene derivatives in the photoactive layer in a bulkheterojunction (BHJ) architecture have demonstrated a steady rise in efficiency and lifetime in recent years.[1,5] This rise has, in part, been due to the large number of novel electron donating semiconductors that have been synthesised. Comparison of the absorption spectra from thienothiophene-based copolymers show that for the 2,7carbazole derivatives, a relative red-shi in the onset of absorption is observed for PCDTTBT-8 compared to the polymer PCDT2BT-8.

Results

Conclusion