Regensburg 2013 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 65: Poster: Organic electronics and photovoltaics (CPP; jointly with HL, O)
HL 65.11: Poster
Wednesday, March 13, 2013, 16:30–18:30, Poster C
The effect of fluorination on the performance of FnZnPc/C60 organic photovoltaic cells — •M. Brendel1,2, A. Steindamm1,2, F. Staub1, and J. Pflaum1,2 — 1Exp. Phys. VI, University of Würzburg, 97074 Würzburg — 2ZAE Bayern, 97074 Würzburg
The material class of phthalocyanines has proven to be a suited donor material in small molecule organic photovoltaic cells (OPVCs). Planar heterojunctions based on zinc phthalocyanine (ZnPc) in combination with the acceptor C60 show high short circuit currents (jsc) of 6.3 mA/cm2 and fill factors (FF) of 51 % [1]. However, due to the small effective band gap Eg,eff of only 1 eV between ionisation potential of the donor and electron affinity of the acceptor, the correlated open circuit voltage (Voc) is limited to 0.5 V. As a possible approach energy levels of Pcs can be modified by substituting hydrogen atoms. With increasing degree of fluorination the position of the HOMO and LUMO levels are shifted to lower energies. In this contribution we investigated the impact of Eg,eff on Voc for a varying degree of fluorination (n = 0, 4, 8, 16) in FnZnPc/C60 OPVCs. First results revealed a significant Voc improvement of 20 % to 0.6 V for F4ZnPc based cells compared to ZnPc, while jsc and FF ideally remained unaffected. However, the gain in Voc is smaller than expected by the difference in ionisation potential which accounts for 0.2 - 0.4 eV. This discrepancy will be analyzed in our studies and will lead to a deeper insight into the origins of Voc and its correlation to the energetics on the molecular entities. Financial support by the BMBF (project GREKOS) and by the DFG (program SPP1355). [1] Z. R. Hong, et al., Appl. Phys. Lett. 2007, 90, 203505