Dresden 2011 – scientific programme
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DS: Fachverband Dünne Schichten
DS 53: Organic Electronics and Photovoltaics IV (jointly with CPP, HL, and O)
DS 53.1: Talk
Thursday, March 17, 2011, 16:15–16:30, GER 38
Energy level alignment at polymer/PCBM heterojunctions under operating conditions in an organic photovoltaic cell structure — •Johannes Frisch1, Andreas Wilke1, Patrick Amsalem1, Jens Niederhausen1, Antje Vollmer2, and Norbert Koch1 — 1Humboldt-Universität zu Berlin, Institut für Physik, Brook-Taylor-Str. 6, D-12489 Berlin, Germany — 2Helmholtz-Zentrum Berlin für Materialien und Energie - Speicherring BESSY II, Berlin, Germany
For heterojunction organic photovoltaic cells (OPVCs) generally vacuum level alignment at the donor/acceptor interface is assumed. In contrast, it has been shown that interface dipoles might occur at organic/organic heterojunctions, which questions the assumption of vacuum level alignment at OPVC interfaces. Therefore, we investigated the energy level alignment at the poly(3-hexylthiophene)/1-(3-methoxycarbonyl)propyl-1-phenyl[6.6]C61 (P3HT:PCBM) heterojunctions with ultraviolet photoelectron spectroscopy (UPS). The valence band of P3HT shifted to higher binding energy by 0.45 eV after deposition of PCBM, while vacuum level alignment was found. This observation would imply an increase of the P3HT ionization energy upon interface formation, which is usually not considered in simple models. The observed phenomenon can be explained either by a structural rearrangement of the donor polymer layer upon acceptor deposition or by surface photovoltage effects that occur during photoemission, which charges the P3HT layer positively whereas negative charges are collected in the PCBM layer.