Perovskite solar cells based on hole-transporting conjugated polymers by direct arylation polycondensation
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Research Letter
Perovskite solar cells based on hole-transporting conjugated polymers by direct arylation polycondensation Wei Li, Takehiko Mori, and Tsuyoshi Michinobu, Department of Materials Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan Address all correspondence to Tsuyoshi Michinobu at [email protected] (Received 12 May 2018; accepted 22 June 2018)
Abstract Direct arylation polycondensation (DArP) is an emerging synthetic method of producing conjugated polymers in an environmentally benign and cost-effective manner. We now report the synthesis of hole-transporting conjugated polymers, namely, DPP-OMe (Mn = 7.9 kg/mol) and DPP-F (Mn = 12.6 kg/mol), under microwave-assisted DArP conditions. These two polymers and the previously synthesized 3,6-Cbz-EDOT were evaluated as hole-transporting materials in mesoscopic perovskite solar cells. 3,6-Cbz-EDOT synthesized by DArP exhibited higher hole mobility and better photovoltaic properties than that synthesized by the Stille polycondensation. Moreover, chemical dopants improved the short-circuit current density (Jsc) and fill factor.
Introduction Hole-transporting conjugated polymers have been an important component in many high-performance thin film devices, such as perovskite solar cells (PSCs) and organic light-emitting diodes (OLEDs).[1–7] Aromatic amine compounds are good examples and they could improve the device performances when they carry holes within the multilayer devices. For example, 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-OMeTAD) has been a benchmark hole-transporting material (HTM) in PSCs,[8] and this was also the case for N,N′ -diphenyl-N, N′ -bis(3-methylphenyl)-1,1′ -diphenyl-4,4′ -diamine and tris (4-carbazoyl-9-ylphenyl)amine in OLEDs.[9] Based on these benchmark compounds, a series of aromatic polyamines, such as poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine],[10] were also developed and their thin films were fabricated by wet processes in the multilayer devices.[11–22] Recently, narrow bandgap p-type semiconducting polymers appeared as high mobility organic materials, which were mainly used in thin film transistors (TFTs) and bulk-heterojunction polymer solar cells.[23–27] These polymers are composed of alternating donor and acceptor structures, and their narrow bandgaps originate from the intramolecular charge–transfer (CT) interactions. For example, 3,6-dithiophen-2-yl-2,5-dihydropyrrole[3,4-c]pyrrole-1,4-dione (DTDPP) is one of the most often used CT chromophores to design high-performance narrow bandgap polymers.[28–30] Due to the lactam structure, they show strong π–π interactions, forming highly crystalline films with high mobilities. Both aromatic polyamines and narrow bandgap p-type polymers have been synthesized by the Pd-catalyzed polycondensation, such as the Suzuki and Stille polycondensations.
However, these conventional polycondensations required the multistep tedious preparation of bifunctional boronic acids (for Suzuki coupling) a
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