TY  - JOUR
A1  - Vandewal, Koen
A1  - Albrecht, Steve
A1  - Hoke, Eric T.
A1  - Graham, Kenneth R.
A1  - Widmer, Johannes
A1  - Douglas, Jessica D.
A1  - Schubert, Marcel
A1  - Mateker, William R.
A1  - Bloking, Jason T.
A1  - Burkhard, George F.
A1  - Sellinger, Alan
A1  - Frechet, Jean M. J.
A1  - Amassian, Aram
A1  - Riede, Moritz K.
A1  - McGehee, Michael D.
A1  - Neher, Dieter
A1  - Salleo, Alberto
T1  - Efficient charge generation by relaxed charge-transfer states at organic interfaces
JF  - Nature materials
N2  - 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 viaweakly allowed, low-energy optical transitions. For a wide range of photovoltaic devices based on polymer: fullerene, small-molecule:C-60 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.
Y1  - 2014
U6  - https://doi.org/10.1038/NMAT3807
SN  - 1476-1122
SN  - 1476-4660
VL  - 13
IS  - 1
SP  - 63
EP  - 68
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Benduhn, Johannes
A1  - Tvingstedt, Kristofer
A1  - Piersimoni, Fortunato
A1  - Ullbrich, Sascha
A1  - Fan, Yeli
A1  - Tropiano, Manuel
A1  - McGarry, Kathryn A.
A1  - Zeika, Olaf
A1  - Riede, Moritz K.
A1  - Douglas, Christopher J.
A1  - Barlow, Stephen
A1  - Marder, Seth R.
A1  - Neher, Dieter
A1  - Spoltore, Donato
A1  - Vandewal, Koen
T1  - Intrinsic non-radiative voltage losses in fullerene-based organic solar cells
JF  - Nature Energy
N2  - Organic solar cells demonstrate external quantum efficiencies and fill factors approaching those of conventional photovoltaic technologies. However, as compared with the optical gap of the absorber materials, their open-circuit voltage is much lower, largely due to the presence of significant non-radiative recombination. Here, we study a large data set of published and new material combinations and find that non-radiative voltage losses decrease with increasing charge-transfer-state energies. This observation is explained by considering non-radiative charge-transfer-state decay as electron transfer in the Marcus inverted regime, being facilitated by a common skeletal molecular vibrational mode. Our results suggest an intrinsic link between non-radiative voltage losses and electron-vibration coupling, indicating that these losses are unavoidable. Accordingly, the theoretical upper limit for the power conversion efficiency of single-junction organic solar cells would be reduced to about 25.5% and the optimal optical gap increases to (1.45-1.65) eV, that is, (0.2-0.3) eV higher than for technologies with minimized non-radiative voltage losses.
Y1  - 2017
U6  - https://doi.org/10.1038/nenergy.2017.53
SN  - 2058-7546
VL  - 2
PB  - Nature Publ. Group
CY  - London
ER  -