Abstract
Polymers based on quinoxaline and indacenodithieno[3,2-b]thiophene (IDTT) withmeta-hexyl-phenyl side chains were synthesized.
Highlights
Bulk-heterojunction polymer solar cells (BHJ PSCs), using a solution-processed active layer composed of an electron-donor and an electronacceptor, sandwiched between ITO and metallic electrodes, can attain promising power conversion efficiencies (PCEs) of 8–9%
Positioning the alkyl side chain in either the para- or metaposition of the phenyl ring has little in uence on the absorption and energy levels as well as the band gaps of corresponding copolymers, it plays an important role in forming a more appropriate and ne-grained nanostructure in the D–A blend
The PIDTT-Q-m:Phenyl-C71-butyric acid methyl ester (PC71BM) device attains a superior photocurrent and a PCE as high as 6.8%. This result is among the highest efficiency achieved for IDTT copolymers used in conversional BHJ PSCs
Summary
As a novel solar energy harvesting medium, polymer solar cells (PSCs) have been intensively investigated in recent years as they offer the potential to be light weight, exible and manufactured on a large-area scale at low cost.[1,2,3,4] So far, bulk-heterojunction polymer solar cells (BHJ PSCs), using a solution-processed active layer composed of an electron-donor and an electronacceptor, sandwiched between ITO and metallic electrodes, can attain promising power conversion efficiencies (PCEs) of 8–9%.5 Conjugated donor–acceptor polymers, combining an electrondonating (D) and an electron-withdrawing (A) moiety, are promising since judicious selection of D and A moieties can tailor the D–A interaction and p-electron delocalization, to achieve tunable band gaps, energy levels and chargeTo date, a variety of electron-rich arenes comprising of multiply fused aromatic systems have been reported.[15]. An IDTT-based polymer with a HOMO level of À5.3 eV and a medium band-gap (Eg) of 1.8 eV was reported by Jen et al, which can attain a PCE of 7%.23 By copolymerizing IDTT with different acceptor units, tunable optoelectronic properties and charge-carrier mobilities were obtained with PCEs around 4–5%.24,25 Several architectural designs of devices incorporating non-halogenated solvents and interfacial engineering have resulted in high PCE of 7%.26,27 to expand the family of ladder-type arenes, most efforts have been focused on the designs of building blocks for polymer backbones,[28,29,30,31,32,33] whilst only a few reports have shed light on the in uence of side chain isomerization.[34,35,36] Recently, we studied two series of thiophene–quinoxaline[37,38,39] and IDT– quinoxaline[40] copolymers and found that using meta-alkylphenyl instead of para-alkyl-phenyl side chains can enhance the solubility, molecular weight and photovoltaic performances of the copolymers.
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