In this work, four fused ring electron acceptors(FREAs), 2F-C5, 2F-C6, 2F-C8 and 2F-C10, are developed to investigate the effect of side-chain size on the molecular properties and photovoltaic performance of FREA syst...In this work, four fused ring electron acceptors(FREAs), 2F-C5, 2F-C6, 2F-C8 and 2F-C10, are developed to investigate the effect of side-chain size on the molecular properties and photovoltaic performance of FREA systematically. The elongation of side-chains in the FREAs not only improves their solubility in the processing solvent, but also enhances their miscibility with the donor PBDB-T. It helps the FREA diffuse into the donor PBDB-T during film-formation, thus leading to the decrease in domain size and domain purity from PBDB-T:2F-C5 to PBDB-T:2F-C10 blend films in sequence. The smaller domain size affords more D/A interfaces to benefit exciton dissociation and inhibit monomolecular recombination. However, severe bimolecular recombination occurs when the domain purity decreases to a critical point. Due to the dual function of the increment of side-chain length, both short-circuit current density(J_(SC)) and fill factor(FF) of devices exhibit an evolution of first increasing then decreasing from 2F-C5, 2F-C6, 2F-C8 to 2F-C10 based OSCs. The PBDB-T:2F-C8 based OSCs get a fine balance in morphology with moderate domain size as well as high domain purity simultaneously for the least charge carrier recombination, thus achieving the highest power conversion efficiency of 12.28% with the best J_(SC)(21.27 mA cm^(-2)) and FF(71.96%).展开更多
Small molecule ladder-type heteroarenes IHBT-2F is designed and synthesized with strong electrondonating and molecular packing properties, where the central unit, fused thienobenzene-thienothiphene (IHBT), is attached...Small molecule ladder-type heteroarenes IHBT-2F is designed and synthesized with strong electrondonating and molecular packing properties, where the central unit, fused thienobenzene-thienothiphene (IHBT), is attached with the strong electron-deficient 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2FIC) as the end group. The counterpart IDBT-2F with indancenodibenzothiophene (IDBT) mainchain is sythesized for comparison, in which thieno[3,2-b]thiophene (TT) core of IHBT is replaced by benzene core. Relative to benzene-core IDBT-2F, TT-core IHBT-2F shows a much higher highest occupied molecular orbital energy level (IHBT-2F:-5.46 eV;IDBT-2F:-5.72 eV) and significantly redshifted absorption, due to the π-donor capability of the sulfur atom, the larger π-conjugation and stronger intermolecular π-π stacking. The as-cast organic solar cells (OSCs) based on blends of PTB7-Th donor and IHBT-2F acceptor without additional treatments exhibit power conversion efficiencies (PCEs) as high as 8.74%, which is much higher than that of PTB7-Th:IDBT-2F (6.73%).展开更多
基金supported by the National Natural Science Foundation of China(21734001,51761165023,21504066,21534003)the Department of the Navy U.S.(N00014-14-1-0580,N00014-16-1-2520)+1 种基金the Ministry of Science and Technology,China(2016YFA0200700)the Natural Science Foundation,U.S.(DMR-1507249,CBET-1639429)~~
基金supported by the National Postdoctoral Program for Innovative Talents (BX201700253)the China Postdoctoral Science Foundation (2017M620068, 2018M630208)+1 种基金the National Natural Science Foundation of China (21673257, 21805288)the Ministry of Science and Technology (2016YFA0200700)
文摘In this work, four fused ring electron acceptors(FREAs), 2F-C5, 2F-C6, 2F-C8 and 2F-C10, are developed to investigate the effect of side-chain size on the molecular properties and photovoltaic performance of FREA systematically. The elongation of side-chains in the FREAs not only improves their solubility in the processing solvent, but also enhances their miscibility with the donor PBDB-T. It helps the FREA diffuse into the donor PBDB-T during film-formation, thus leading to the decrease in domain size and domain purity from PBDB-T:2F-C5 to PBDB-T:2F-C10 blend films in sequence. The smaller domain size affords more D/A interfaces to benefit exciton dissociation and inhibit monomolecular recombination. However, severe bimolecular recombination occurs when the domain purity decreases to a critical point. Due to the dual function of the increment of side-chain length, both short-circuit current density(J_(SC)) and fill factor(FF) of devices exhibit an evolution of first increasing then decreasing from 2F-C5, 2F-C6, 2F-C8 to 2F-C10 based OSCs. The PBDB-T:2F-C8 based OSCs get a fine balance in morphology with moderate domain size as well as high domain purity simultaneously for the least charge carrier recombination, thus achieving the highest power conversion efficiency of 12.28% with the best J_(SC)(21.27 mA cm^(-2)) and FF(71.96%).
基金NSFC (21504058)NSFC/RGC Joint Research Scheme No. N_CUHK418/17+1 种基金Research Grant Council of Hong Kong (General Research Fund No. 14314216)the beam time and technical supports provided by 19U2 beamline at SSRF, Shanghai
文摘Small molecule ladder-type heteroarenes IHBT-2F is designed and synthesized with strong electrondonating and molecular packing properties, where the central unit, fused thienobenzene-thienothiphene (IHBT), is attached with the strong electron-deficient 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2FIC) as the end group. The counterpart IDBT-2F with indancenodibenzothiophene (IDBT) mainchain is sythesized for comparison, in which thieno[3,2-b]thiophene (TT) core of IHBT is replaced by benzene core. Relative to benzene-core IDBT-2F, TT-core IHBT-2F shows a much higher highest occupied molecular orbital energy level (IHBT-2F:-5.46 eV;IDBT-2F:-5.72 eV) and significantly redshifted absorption, due to the π-donor capability of the sulfur atom, the larger π-conjugation and stronger intermolecular π-π stacking. The as-cast organic solar cells (OSCs) based on blends of PTB7-Th donor and IHBT-2F acceptor without additional treatments exhibit power conversion efficiencies (PCEs) as high as 8.74%, which is much higher than that of PTB7-Th:IDBT-2F (6.73%).