Berlin 2015 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 30: P2: Organic Electronics and Photovoltaics
CPP 30.9: Poster
Dienstag, 17. März 2015, 14:00–16:00, Poster B
Determination of the CT energy of organic small molecule solar cells by different methods — •Theresa Linderl, Mark Gruber, Stefan Grob, Ulrich Hörmann, Alexander Hofmann, and Wolfgang Brütting — Universität Augsburg, 86135 Augsburg, Germany
The open-circuit voltage VOC of organic solar cells is limited by the formation of a charge transfer (CT) state at the donor-acceptor interface. We determine the energy of the CT state for small molecule organic solar cells by different methods and compare the obtained values. Electroluminescence (EL) spectroscopy on heterojunction devices together with the spectra of single layer devices of the individual materials are used to determine the CT feature in the spectrum. For voltages just above VOC an additional feature can be detected in the low energy range that cannot be attributed to any of the individual materials. Together with sensitive IPCE (Incident Photon to Current Efficiency) measurements the CT energy can be determined and compared to the values derived from temperature dependent measurements of the current-voltage (j-V) characteristics. Both, dark and illuminated j-V curves can be used to determine the CT gap energy. We find that the energy loss from the CT energy to q· VOC at room temperature is 0.55 eV for all investigated material systems.