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DS: Fachverband Dünne Schichten
DS 14: Organic Electronics and Photovoltaics HL-I (jointly with CPP, HL, and O)
DS 14.3: Talk
Monday, March 14, 2011, 18:15–18:30, FOE Anorg
Open circuit voltage as function of mixing ratio in ZnPc:C60 bulk heterojunction organic solar cells — •Steffen Pfuetzner, Wolfgang Tress, Selina Olthof, Max Tietze, Jan Meiss, Karl Leo, and Moritz Riede — Institut für Angewandte Photophysik, Technische Universität Dresden, D-01069 Dresden, Germany
We characterize organic solar cells composed of mixed layers of ZnPc:C60 as photoactive layer embedded between a p-doped hole transport (HTL) and an undoped electron transport layer. By varying the mixing ratio of the photoactive bulk heterojunction from 6:1 (ZnPc:C60) to 1:6 by volume, we observe significant changes of VOC from 0.54 to 0.63 V. To exclude that this increase with higher C60 content is caused by the increased contact area of C60 to the HTL, behaving as an additional exciton separating interface, J(V) measurements under spectral narrow red and blue illumination are performed. Independent of where absorption takes place (for red in ZnPc, for blue in C60), VOC is not affected significantly. Hence, we attribute the changes in VOC not to an additional separating interface, but to an intrinsic blend layer effect. Further investigations using ultraviolet photoelectron spectroscopy measurements, absorption measurements, and HTL variations with different highest occupied molecular orbitals indicate as reason HOMO and LUMO shifts of C60 and ZnPc as a function of the mixing ratio.