Abstract
3-(2-Octyldodecyl)thieno[3,2-b]thiophen was successfully synthesized as a new π-bridge with a long branched side alkyl chain. Two donor-π-bridge-acceptor type copolymers were designed and synthesized by combining this π-bridge structure, a fluorinated benzothiadiazole acceptor unit, and a thiophene or thienothiophene donor unit, (PT-ODTTBT or PTT-ODTTBT respectively) through Stille polymerization. Inverted OPV devices with a structure of ITO/ZnO/polymer:PC71BM/MoO3/Ag were fabricated by spin-coating in ambient atmosphere or N2 within a glovebox to evaluate the photovoltaic performance of the synthesized polymers (effective active area: 0.09 cm2). The PTT-ODTTBT:PC71BM-based structure exhibited the highest organic photovoltaic (OPV) device performance, with a maximum power conversion efficiency (PCE) of 7.05 (6.88 ± 0.12)%, a high short-circuit current (Jsc) of 13.96 mA/cm2, and a fill factor (FF) of 66.94 (66.47 ± 0.63)%; whereas the PT-ODTTBT:PC71BM-based device achieved overall lower device performance. According to GIWAXS analysis, both neat and blend films of PTT-ODTTBT exhibited well-organized lamellar stacking, leading to a higher charge carrier mobility than that of PT-ODTTBT. Compared to PT-ODTTBT containing a thiophene donor unit, PTT-ODTTBT containing a thienothiophene donor unit exhibited higher crystallinity, preferential face-on orientation, and a bicontinuous interpenetrating network in the film, which are responsible for the improved OPV performance in terms of high Jsc, FF, and PCE.
Highlights
Bulk heterojunction organic photovoltaics (OPVs) have received a great deal of attention owing to their unique advantages including low cost, mechanical flexibility, and ease processability [1–5]
Compared to PT-ODTTBT containing a thiophene donor unit, PTT-ODTTBT containing a thienothiophene donor unit exhibited higher crystallinity, preferential face-on orientation, and a bicontinuous interpenetrating network in the film, which are responsible for the improved OPV performance in terms of high Jsc, fill factor (FF), and power conversion efficiency (PCE)
We have previously reported several new D–π–A type polymers consisting of linear alkyl-substituted TT as a π-bridge (PBDT–TPD, PBDT–ttTPD, PBDTT–TPD, and PBDTT–ttTPD) that showed excellent OPV device performance in single/tandem solar cells owing to their well-ordered orientation and enhanced hole mobility [22]
Summary
Bulk heterojunction organic photovoltaics (OPVs) have received a great deal of attention owing to their unique advantages including low cost, mechanical flexibility, and ease processability [1–. Their photovoltaic performance has rapidly advanced through the development of state-of-the-art electron donor/acceptor or interfacial materials, as well as optimization of the OPV device fabrication process via adjusting additives, solvents, and thermal treatment They showed enhanced power conversion efficiencies (PCEs) of over 15% and 17% for single junction devices and double junction devices, respectively [6,7,8,9,10]. TT exhibited a well-organized crystal domain and high charge carrier mobility and can be used in the development of efficient OPVs. We have previously reported several new D–π–A type polymers consisting of linear alkyl-substituted TT as a π-bridge (PBDT–TPD, PBDT–ttTPD, PBDTT–TPD, and PBDTT–ttTPD) that showed excellent OPV device performance in single/tandem solar cells owing to their well-ordered orientation and enhanced hole mobility [22].
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