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  - Gehrig, Dominik W.
A1  - Roland, Steffen
A1  - Howard, Ian A.
A1  - Kamm, Valentin
A1  - Mangold, Hannah
A1  - Neher, Dieter
A1  - Laquai, Frederic
T1  - Efficiency-limiting processes in low-bandgap polymer:Perylene diimide photovoltaic blends
JF  - The journal of physical chemistry : C, Nanomaterials and interfaces
N2  - The charge generation and recombination processes following photo-excitation of a low-bandgap polymer:perylene diimide photovoltaic blend are investigated by transient absorption pump-probe spectroscopy covering a dynamic range from femto-to microseconds to get insight into the efficiency-limiting photophysical processes. The several tens of picoseconds, and its efficiency is only half of that in a polymer:fullerene photoinduced electron transfer from the polymer to the perylene acceptor takes up to blend. This reduces the short-circuit current. Time-delayed collection field experiments reveal that the subsequent charge separation is strongly field-dependent, limiting the fill factor and lowering the short-circuit current in polymer:PDI devices. Upon excitation of the acceptor in the low-bandgap polymer blend, the PDI exciton undergoes charge transfer on a time scale of several tens of picoseconds. However, a significant fraction of the charges generated at the interface are quickly lost because of fast geminate recombination. This reduces the short-circuit current even further, leading to a scenario in which only around 2596 of the initial photoexcitations generate free charges that can potentially contribute to the photocurrent. In summary, the key photophysical limitations of perylene diimide as an acceptor in low-bandgap polymer blends appear at the interface between the materials, with the kinetics of both charge generation and separation inhibited as compared to that of fullerenes.
Y1  - 2014
U6  - https://doi.org/10.1021/jp503366m
SN  - 1932-7447
VL  - 118
IS  - 35
SP  - 20077
EP  - 20085
PB  - American Chemical Society
CY  - Washington
ER  -