Dresden 2014 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 28: Organic electronics and photovoltaics I (organized by DS)

HL 28.4: Vortrag

Montag, 31. März 2014, 18:45–19:00, CHE 91

The effect of gradual fluorination on the opto-electronic properties of FnZnPc/C60 bilayer cells — •M. Brendel1, A. Steindamm1, A. Topczak1, and J. Pflaum1,21Exp. Phys. VI, JMU Würzburg, 97074 Würzburg — 2ZAE Bayern, 97074 Würzburg

The respective position of energy levels at the donor/acceptor heterojunction is crucial for the resulting parameters of an organic solar cell. For instance the open circuit voltage (Voc) is correlated to the energy difference between the highest occupied molecular orbital (HOMO) of the donor and the lowest unoccupied molecular orbital (LUMO) of the acceptor, the so-called effective band gap (Eg,eff). To gain insights into this correlation, tailoring of energy levels by chemical modification is a powerful approach. In this contribution, we investigate the impact of gradual fluorination of zinc phthalocyanine on the opto-electronic properties of FnZnPc/C60 (n=0,4,8,16) bilayer cells. Upon fluorination, HOMO and LUMO levels are shifted towards lower energies. The gain in Voc for F4ZnPc/C60 and F8ZnPc/C60 by 11% and 23% respectively, compared to ZnPc/C60, confirms qualitatively the expected energy level scheme. Besides, the differences between e· Δ Voc and Δ Eg,eff hint at the occurrence of dipoles and their gain in strength with increasing degree of fluorination. As will be shown, this dipol can be correctly accounted for in a plate capacitor geometry, considering image charges at the interface induced by electronegative fluorine in the immediate vicinity of C60 molecules. We thank S. Sundarray and P. Erk from BASF for providing F4ZnPc. Financial support by the DFG (program SPP1355) and the BMBF (GREKOS program).

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