Influence of Phase Segregation on Recombination Dynamics in Organic Bulk‐Heterojunction Solar Cells |
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| Authors: | Andreas Baumann Tom J. Savenije Dharmapura Hanumantharaya K. Murthy Martin Heeney Vladimir Dyakonov Carsten Deibel |
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| Affiliation: | 1. Experimental Physics VI, Julius‐Maximilians‐University of Würzburg, 97074 Würzburg, Germany;2. Experimental Physics VI, Julius‐Maximilians‐University of Würzburg, 97074 Würzburg, Germany, Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, 2628 BL Delft, The Netherlands;3. Optoelectronic Materials Section, Department of Chemical Engineering, Delft University of Technology, 2628 BL Delft, The Netherlands;4. Department of Chemistry, Imperial College London, London, SW7 2AZ, United Kingdom;5. Experimental Physics VI, Julius‐Maximilians‐University of Würzburg, 97074 Würzburg, Germany, Bavarian Center for Applied Energy Research e.V. (ZAE Bayern), 97074 Würzburg, Germany |
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| Abstract: | The recombination dynamics of charge carriers in organic bulk‐heterojunction (BHJ) solar cells made of the blend system poly(2,5‐bis(3‐dodecylthiophen‐2‐yl)thieno[2,3‐b]thiophene) (pBTCT‐C12):[6,6]‐phenyl‐C61‐butyric acid methyl ester (PC61BM) with a donor–acceptor ratio of 1:1 and 1:4 are studied here. The techniques of charge‐carrier extraction by linearly increasing voltage (photo‐CELIV) and, as local probe, time‐resolved microwave conductivity are used. A difference of one order of magnitude is observed between the two blends in the initially extracted charge‐carrier concentration in the photo‐CELIV experiment, which can be assigned to an enhanced geminate recombination that arises through a fine interpenetrating network with isolated phase regions in the 1:1 pBTCT‐C12:PC61BM BHJ solar cells. In contrast, extensive phase segregation in 1:4 blend devices leads to an efficient polaron generation that results in an increased short‐circuit current density of the solar cells. For both studied ratios a bimolecular recombination of polarons is found using the complementary experiments. The charge‐carrier decay order of above two for temperatures below 300 K can be explained on the basis of a release of trapped charges. This mechanism leads to delayed bimolecular recombination processes. The experimental findings can be generalized to all polymer:fullerene blend systems allowing for phase segregation. |
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| Keywords: | charge transport organic solar cells phase segregation polaron recombination transient microwave conductivity |
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