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Tuning the Molecular Weight of the Electron Accepting Polymer in All‐Polymer Solar Cells: Impact on Morphology and Charge Generation
Author(s) -
Deshmukh Kedar D.,
Matsidik Rukiya,
Prasad Shyamal K. K.,
Connal Luke A.,
Liu Amelia C. Y.,
Gann Eliot,
Thomsen Lars,
Hodgkiss Justin M.,
Sommer Michael,
McNeill Christopher R.
Publication year - 2018
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201707185
Subject(s) - materials science , polymer , organic solar cell , acceptor , polymer solar cell , chemical engineering , solar cell , chemical physics , spectroscopy , analytical chemistry (journal) , optoelectronics , organic chemistry , composite material , chemistry , physics , quantum mechanics , engineering , condensed matter physics
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 M n = 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 M n = 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 M n = 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.