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The conversion of absorbed light into electricity in organic semiconductors comprises several elementary processes, notably the generation of excitons in the conjugated material, their dissociation into interfacial charge transfer states (CTs), the splitup of these interfacial excitatioins into pairs of free electrons and holes, and finally free charge extraction in competition to non-geminate recombination. A major challenge in understanding the photovoltaic properties of solar cells is to disentangle how electric field, light intensity and excitation energy affect these elementary steps. We have, therefore, established a time-delayed collection field setup which is worldwide unique with regard to temporal resolution and sensitivity. Current research topics concern the influence of the incident photon energy on the efficiency of charge generation and the effect of energetic disorder on the rate of free charge recombination and with that on the open circuit voltage of organic solar cells. These investigations aim at the proposed influence of excess energy on the charge carrier dynamics in organic solar cells.
J. Kurpiers, D. Neher, "Dispersive Non-Geminate Recombination in an Amorphous Polymer:Fullerene Blend", Scientific Reports 6, 26832 (2016), DOI: 10.1038/srep26832
J. Kniepert, I. Lange, J. Heidbrink, J. Kurpiers, T.J.K. Brenner, L.J.A. Koster, D. Neher, “Effect of Solvent Additive on Generation, Recombination, and Extraction in PTB7:PCBM Solar Cells: A Conclusive Experimental and Numerical Simulation Study”, The Journal of Physical Chemistry C 119, 8310-8320 (2015), DOI: 10.1021/jp512721e
W. Li, S. Albrecht, L. Yang, S. Roland, J.R. Tumbleston, T. McAfee, L. Yan, M.A. Kelly, H. Ade, D. Neher, W. You, "Mobility-Controlled Performance of Thick Solar Cells Based on Fluorinated Copolymers", Journal of the American Chemical Society 136, 15566-15576 (2014), DOI: 10.1021/ja5067724
S. Roland, M. Schubert, B.A. Collins, J. Kurpiers, Z. Chen , A. Facchetti , H. Ade, D. Neher, “Fullerene-Free Polymer Solar Cells with Highly Reduced Bimolecular Recombination and Field-Independent Charge Carrier Generation”, Journal of Physical Chemistry Letters 5, 2815-2822 (2014), DOI: 10.1021/jz501506z
S. Albrecht, K. Vandewal, J.R. Tumbleston, F.S.U. Fischer, J.D. Douglas, J.M.J. Fréchet, S. Ludwigs, H. Ade, A. Salleo, D. Neher, “On the Efficiency of Charge Transfer State Splitting in Polymer:Fullerene Solar Cells”, Advanced Materials 26, 2533-2539 (2014), DOI: 10.1002/adma.201305283