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Charge Photogeneration in Organic Photovoltaics: Role of Hot versus Cold Charge‐Transfer Excitons |
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| Authors: | Bhoj R Gautam Robert Younts Wentao Li Liang Yan Evgeny Danilov Erik Klump Iordania Constantinou Franky So Wei You Harald Ade Kenan Gundogdu |
| Institution: | 1. Department of Physics and Organic and Carbon Electronics Laboratory, North Carolina State University, Raleigh, NC, USA;2. Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA;3. Department of Chemistry, North Carolina State University, Raleigh, NC, USA;4. Department of Material Science and Engineering, North Carolina State University, Raleigh, NC, USA |
| Abstract: | The role of excess excitation energy on long‐range charge separation in organic donor/acceptor bulk heterojunctions (BHJs) continues to be unclear. While ultrafast spectroscopy results argue for efficient charge separation through high‐energy charge‐transfer (CT) states within the first picosecond (ps) of excitation, charge collection measurements suggest excess photon energy does not increase the current density in BHJ devices. Here, the population dynamics of charge‐separated polarons upon excitation of high‐energy polymer states and low‐energy interfacial CT states in two polymer/fullerene blends from ps to nanosecond time scales are studied. It is observed that the charge‐separation dynamics do not show significant dependence on excitation energy. These results confirm that excess exciton energy is not necessary for the effective generation of charges. |
| Keywords: | conjugated polymers organic photovoltaics ultrafast spectroscopy charge transfer exciton |