Tuning the Molecular Weight of the Electron Accepting Polymer in All‐Polymer Solar Cells: Impact on Morphology and Charge Generation |
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| Authors: | Rukiya Matsidik Shyamal K K Prasad Luke A Connal Amelia C Y Liu Lars Thomsen Justin M Hodgkiss Christopher R McNeill |
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| Affiliation: | 1. Institut für Makromolekulare Chemie, Universit?t Freiburg, Freiburg, Germany;2. MacDiarmid Institute for Advanced Materials and Nanotechnology, and School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand;3. Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory, Australia;4. Monash Centre of Electron Microscopy and School of Physics and Astronomy, Monash University, Clayton, Victoria, Australia;5. Australian Synchrotron, Clayton, VIC, Australia;6. Department of Materials Science and Engineering, Monash University, Victoria, Australia |
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| Abstract: | Molecular weight is an important factor determining the morphology and performance of all‐polymer solar cells. Through the application of direct arylation polycondention, a series of batches of a fluorinated naphthalene diimide‐based acceptor polymer are prepared with molecular weight varying from Mn = 20 to 167 kDa. Used in conjunction with a common low bandgap donor polymer, the effect of acceptor molecular weight on solar cell performance, morphology, charge generation, and transport is explored. Increasing the molecular weight of the acceptor from Mn = 20 to 87 kDa is found to increase cell efficiency from 2.3% to 5.4% due to improved charge separation and transport. Further increasing the molecular weight to Mn = 167 kDa however is found to produce a drop in performance to 3% due to liquid–liquid phase separation which produces coarse domains, poor charge generation, and collection. In addition to device studies, a systematic investigation of the microstructure and photophysics of this system is presented using a combination of transmission electron microscopy, grazing‐incidence wide‐angle X‐ray scattering, near‐edge X‐ray absorption fine‐structure spectroscopy, photoluminescence quenching, and transient absorption spectroscopy to provide a comprehensive understanding of the interplay between morphology, photophysics, and photovoltaic performance. |
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| Keywords: | all‐polymer solar cells molecular weight morphology photophysics |
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