Photo‐induced Charge Transfer and Relaxation of Persistent Charge Carriers in Polymer/Nanocrystal Composites for Applications in Hybrid Solar Cells |
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Authors: | Marc Daniel Heinemann Karsten von Maydell Folker Zutz Joanna Kolny‐Olesiak Holgert Borchert Ingo Riedel Jürgen Parisi |
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Affiliation: | 1. University of Oldenburg, Department of Physics, Energy and Semiconductor Research Laboratory Carl‐von‐Ossietzky‐Str. 9‐11, 26129 Oldenburg (Germany);2. EWE Research Center for Energy Technology – NEXT ENERGY Carl‐von‐Ossietzky‐Str. 15, 26129 Oldenburg (Germany) |
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Abstract: | The photo‐induced charge transfer and the dynamics of persistent charge carriers in blends of semiconducting polymers and nanocrystals are investigated. Regioregular poly(3‐hexylthiophene) (P3HT) is used as the electron donor material, while the acceptor moiety is established by CdSe nanocrystals (nc‐CdSe) prepared via colloidal synthesis. As a reference system, organic blends of P3HT and 6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) are studied as well. The light‐induced charge transfer between P3HT and the acceptor materials is studied by photoluminescence (PL), photo‐induced absorption (PIA) and light‐induced electron spin resonance spectroscopy (LESR). Compared to neat P3HT samples, both systems show an intensified formation of polarons in the polymer upon photo‐excitation, pointing out successful separation of photogenerated charge carriers. Additionally, relaxation of the persistent charge carriers is investigated, and significant differences are found between the hybrid composite and the purely organic system. While relaxation, reflected in the transient signal decay of the polaron signal, is fast in the organic system, the hybrid blends exhibit long‐term persistence. The appearance of a second, slow recombination channel indicates the existence of deep trap states in the hybrid system, which leads to the capture of a large fraction of charge carriers. A change of polymer conformation due to the presence of nc‐CdSe is revealed by low temperature LESR measurements and microwave saturation techniques. The impact of the different recombination behavior on the photovoltaic efficiency of both systems is discussed. |
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Keywords: | Hybrid materials Solar cells Conjugated polymers CdSe nanocrystals Charge transfer |
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