Regensburg 2013 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 61: Organic Electronics and Photovoltaics I (jointly with CPP, DS, and HL)

O 61.1: Hauptvortrag

Donnerstag, 14. März 2013, 09:30–10:00, H34

Influence of morphology on organic solar cell performance comparing crystalline diindenoperylene (DIP) and its amorphous derivative tetraphenyldibenzoperiflanthene (DBP) — Stefan Grob, Mark Gruber, Ulrich Hörmann, and •Wolfgang Brütting — Institute of Physics, University of Augsburg, Germany

The DIP molecule, consisting of seven benzene and two cyclopentadiene rings, forms the backbone of the DBP molecule, which has two further benzene rings and four additional, rotatable phenyl groups. Compared to the planar arrangement of DIP, the four phenyl groups give DBP a more three-dimensional shape, changing the growth behavior in thin films completely. While we observe crystalline domains of almost upright standing DIP, layers of DBP exhibit an amorphous character and therefore a relatively small exciton diffusion length, being about ten times shorter than that of its crystalline counterpart. However, the drawback of the upright standing arrangement of DIP molecules is the unfavorable orientation of the transition dipole moment resulting in a low absorption coefficient. In contrast, the structural disorder in DBP combined with a little smaller optical gap leads to light absorption which is about eight times higher than in DIP, whereby the short-circuit current density almost doubles in corresponding solar cell devices. Moreover, open circuit voltages are high and - due to similar energy level alignments - comparable, by using the materials both as donor with C60 (0.9 V) and as acceptor with 6T (1.2 V). Based on these results, we discuss the influence of different film structure and morphology on electrical transport and device performance.