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HL: Fachverband Halbleiterphysik

HL 78: Joint Session: Organic Electronics and Photovoltaics IV

HL 78.4: Vortrag

Donnerstag, 17. März 2011, 17:00–17:15, GER 38

Comparison of the operation of standard and inverted P3HT:PCBM solar cells — •Thomas J.K. Brenner, Yana Vaynzof, Zhe Li, Dinesh Kabra, Richard H. Friend, and Christopher R. McNeill — Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Ave., Cambridge CB3 0HE, United Kingdom

Inverted organic solar cells have attracted recent attention due to their enhanced environmental stability compared to the standard device architecture. However to date inverted cells have shown poorer efficiencies compared to the standard geometry. To clarify the origin of this behaviour, we have investigated inverted (ITO/ZnO/P3HT:PCBM/ WO3/Ag) and regular (ITO/PEDOT:PSS/P3HT:PCBM/Al) P3HT:PCBM solar cells with different active layer thickness. Using white light bias external quantum efficiency and photocurrent transient measurements, we propose an explanation for the reduced performance of inverted cells. Whereas for inverted devices high EQEs of up to 68% are measured under low light intensities (3 mW/cm²), EQE drops with increasing white light bias (up to 140 mW/cm²) down to 20%. This drop is accompanied by a severe distortion of the spectra. For increased thickness (from 90 nm to 550 nm), the drop and shape change can be seen at lower intensities. For regular devices we also observe a drop in EQE, however they still resemble the absorption spectrum showing minor distortion. Unbalanced charge transport and/or unfavourable vertical phase separation in inverted devices are presented as likely causes of the observed behaviour.