Efficient charge generation by relaxed charge-transfer states at organic interfaces
Albrecht, Steve N.
Hoke, Eric T.
Douglas, Jessica D.
Mateker, William R.
Bloking, Jason T.
Burkhard, George F.
Riede, Moritz Kilian
McGehee, Michael D.
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
Chemical Science Program
KAUST Solar Center (KSC)
Materials Science and Engineering Program
Organic Electronics and Photovoltaics Group
Permanent link to this recordhttp://hdl.handle.net/10754/563088
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AbstractInterfaces between organic electron-donating (D) and electron-accepting (A) materials have the ability to generate charge carriers on illumination. Efficient organic solar cells require a high yield for this process, combined with a minimum of energy losses. Here, we investigate the role of the lowest energy emissive interfacial charge-transfer state (CT1) in the charge generation process. We measure the quantum yield and the electric field dependence of charge generation on excitation of the charge-transfer (CT) state manifold via weakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer:fullerene, small-molecule:C60 and polymer:polymer blends, our study reveals that the internal quantum efficiency (IQE) is essentially independent of whether or not D, A or CT states with an energy higher than that of CT1 are excited. The best materials systems show an IQE higher than 90% without the need for excess electronic or vibrational energy. © 2014 Macmillan Publishers Limited.
SponsorsThis publication was supported by the Center for Advanced Molecular Photovoltaics (Award No KUS-C1-015-21) and the Department of Energy, Laboratory Directed Research and Development funding, under contract DE-AC02-76SF00515. The PCDTBT used in this work was provided by St-Jean Photochemicals. M. K. R. acknowledges financial support by the BMBF through project 03IP602 and J. W. acknowledges support from the Heinrich-Boll-Stiftung. S.A. and M.S. acknowledge financial support by the BMBF within PVcomB (FKZ 03IS2151D) and the DFG (SPP 1355). D.N. thanks the DFG for financially supporting a travel grant. K.R.G. and A.A. acknowledge SABIC for a post-doctoral fellowship. The authors thank J. Kurpiers for technical assistance with the TDCF set-up.