TY  - JOUR
A1  - Schubert, Marcel
A1  - Collins, Brian A.
A1  - Mangold, Hannah
A1  - Howard, Ian A.
A1  - Schindler, Wolfram
A1  - Vandewal, Koen
A1  - Roland, Steffen
A1  - Behrends, Jan
A1  - Kraffert, Felix
A1  - Steyrleuthner, Robert
A1  - Chen, Zhihua
A1  - Fostiropoulos, Konstantinos
A1  - Bittl, Robert
A1  - Salleo, Alberto
A1  - Facchetti, Antonio
A1  - Laquai, Frederic
A1  - Ade, Harald W.
A1  - Neher, Dieter
T1  - Correlated donor/acceptor crystal orientation controls photocurrent generation in all-polymer solar cells
JF  - Advanced functional materials
N2  - New polymers with high electron mobilities have spurred research in organic solar cells using polymeric rather than fullerene acceptors due to their potential of increased diversity, stability, and scalability. However, all-polymer solar cells have struggled to keep up with the steadily increasing power conversion efficiency of polymer: fullerene cells. The lack of knowledge about the dominant recombination process as well as the missing concluding picture on the role of the semi-crystalline microstructure of conjugated polymers in the free charge carrier generation process impede a systematic optimization of all-polymer solar cells. These issues are examined by combining structural and photo-physical characterization on a series of poly(3-hexylthiophene) (donor) and P(NDI2OD-T2) (acceptor) blend devices. These experiments reveal that geminate recombination is the major loss channel for photo-excited charge carriers. Advanced X-ray and electron-based studies reveal the effect of chloronaphthalene co-solvent in reducing domain size, altering domain purity, and reorienting the acceptor polymer crystals to be coincident with those of the donor. This reorientation correlates well with the increased photocurrent from these devices. Thus, effi cient split-up of geminate pairs at polymer/polymer interfaces may necessitate correlated donor/acceptor crystal orientation, which represents an additional requirement compared to the isotropic fullerene acceptors.
Y1  - 2014
U6  - https://doi.org/10.1002/adfm.201304216
SN  - 1616-301X
SN  - 1616-3028
VL  - 24
IS  - 26
SP  - 4068
EP  - 4081
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
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  -