The influence of solid‐state microstructure on the origin and yield of long‐lived photogenerated charge in neat semiconducting polymers

Journal of Polymer Science, Part B: Polymer Physics - Tập 50 Số 1 - Trang 27-37 - 2012
Ruipeng Li1, Jennifer A. Nekuda Malik2, Gianluca Latini3, Smita Dayal1, Nikos Kopidakis1, Carlos Silva4, Natalie Stingelin2,5,6,7, Garry Rumbles1,8,6,7
1Chemical and Materials Science Center, National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401
2Department of Materials and Centre for Plastic Electronics, Imperial College London, London, United Kingdom
3Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia, via Barsanti, 73010 Arnesano (LE), Italy
4Department of Physics, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
5Department of Materials, Swiss Federal Institute of Technology (ETH) Zürich, Zürich, Switzerland
6Garry Rumbles, Chemical and Materials Science Center, National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401
7Natalie Stingelin, Department of Materials and Centre for Plastic Electronics, Imperial College London, London, United Kingdom
8Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado 80309

Tóm tắt

AbstractThe influence of solid‐state microstructure on the optoelectronic properties of conjugated polymers is widely recognized, but still poorly understood. Here, we show how the microstructure of conjugated polymers controls the yield and decay dynamics of long‐lived photogenerated charge in neat films. Poly(3‐hexylthiophene) was used as a model system. By varying the molecular weight, we drive a transition in the polymer microstructure from nonentangled, chain‐extended, paraffinic‐like to entangled, semicrystalline (MW = 5.5–347 kg/mol). The molecular weight range at which this transition occurs (MW = 40–50 kg/mol) can be deduced from the drastic change in elongation at break found in tensile tests. Linear absorption measurements of free‐exciton bandwidth and time‐resolved microwave conductivity (TRMC) measurements of transient photoconductance track the concomitant evolution in optoelectronic properties of the polymer as a function of MW. TRMC measurements show that the yield of free photogenerated charge increases with increasing molecular weight in the paraffinic regime and saturates at the transition into the entangled, semicrystalline regime. This transition in carrier yield correlates with a sharp transition in free‐exciton bandwidth and decay dynamics at a similar molecular weight. We propose that the transition in microstructure controls the yield and decay dynamics of long‐lived photogenerated charge. The evolution of a semicrystalline structure with well‐defined interfaces between amorphous and crystalline domains of the polymer is required for spatial separation of the electron and hole. This structural characteristic not only largely controls the yield of free charges, but also serves as a recombination center, where mobile holes encounter a bath of dark electrons resident in the amorphous phase and recombine with quasi first‐order kinetics. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

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Journal of Polymer Science, Part B: Polymer Physics

Tập 50 Số 1

27-37

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