Ultrafast excited state dynamics of a bithiophene-isoindigo copolymer obtained by direct arylation polycondensation and its application in indium tin oxide-free solar cells |
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| Authors: | Newayemedhin A. Tegegne Zelalem Abdissa Wendimagegn Mammo Mats R. Andersson Derck Schlettwein Heinrich Schwoerer |
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| Affiliation: | 1. Physics Department, Laser Research Institute, Stellenbosch University, Stellenbosch, South Africa;2. Science Faculty, Department of Chemistry, Addis Ababa University, P.O. Box 33658, Addis Ababa, Ethiopia;3. Future Industries Institute, University of South Australia, Mawson Lakes Boulevard, Mawson Lakes, South Australia, 5095 Australia;4. Institute of Applied Physics, Justus-Liebig-University, Heinrich Buff Ring 16, 35392 Giessen, Germany |
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| Abstract: | A low band gap copolymer, P2TI (Eg = 1.6.eV), with bithiophene as donor and isoindigo as acceptor units is designed and synthesized by the direct arylation polycondensation (DAP) method. Absorbance of the polymer spans from 300 to 780 nm. It exhibits an absorption coefficient (ε) of 96 L/g cm in solution at its maxima. A HOMO level of −5.42 eV and LUMO level of −3.72 eV is measured by square wave voltammetry. ITO-free solar cells fabricated using a P2TI :PCBM71 bulk heterojunction shows a moderate efficiency of 1.02% with a high open circuit voltage of 0.81 V. An intramolecular charge transfer state is found in the relaxation of P2TI in solution, which is generated with a time constant of 2 ps as measured by femtosecond-transient absorption spectroscopy. Charge carriers were generated in <250 fs in P2TI: PCBM71 films. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1475–1483 |
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| Keywords: | charge transfer copolymer photophysics UV-vis spectroscopy |
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