TY  - JOUR
A1  - Li, Wentao
A1  - Abrecht, Steve
A1  - Yang, Liqiang
A1  - Roland, Steffen
A1  - Tumbleston, John R.
A1  - McAfee, Terry
A1  - Yan, Liang
A1  - Kelly, Mary Allison
A1  - Ade, Harald W.
A1  - Neher, Dieter
A1  - You, Wei
T1  - Mobility-controlled performance of thick solar cells based on fluorinated copolymers
JF  - Journal of the American Chemical Society
N2  - Developing novel materials and device architectures to further enhance the efficiency of polymer solar cells requires a fundamental understanding of the impact of chemical structures on photovoltaic properties. Given that device characteristics depend on many parameters, deriving structureproperty relationships has been very challenging. Here we report that a single parameter, hole mobility, determines the fill factor of several hundred nanometer thick bulk heterojunction photovoltaic devices based on a series of copolymers with varying amount of fluorine substitution. We attribute the steady increase of hole mobility with fluorine content to changes in polymer molecular ordering. Importantly, all other parameters, including the efficiency of free charge generation and the coefficient of nongeminate recombination, are nearly identical. Our work emphasizes the need to achieve high mobility in combination with strongly suppressed charge recombination for the thick devices required by mass production technologies.
Y1  - 2014
U6  - https://doi.org/10.1021/ja5067724
SN  - 0002-7863
VL  - 136
IS  - 44
SP  - 15566
EP  - 15576
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Albrecht, Steve
A1  - Vandewal, Koen
A1  - Tumbleston, John R.
A1  - Fischer, Florian S. U.
A1  - Douglas, Jessica D.
A1  - Frechet, Jean M. J.
A1  - Ludwigs, Sabine
A1  - Ade, Harald W.
A1  - Salleo, Alberto
A1  - Neher, Dieter
T1  - On the efficiency of charge transfer state splitting in polymer: Fullerene solar cells
JF  - Advanced materials
KW  - organic solar cells
KW  - charge generation
KW  - geminate recombination
KW  - charge transfer states
KW  - driving force
KW  - excess energy
KW  - morphology
KW  - spectroelectrochemistry
Y1  - 2014
U6  - https://doi.org/10.1002/adma.201305283
SN  - 0935-9648
SN  - 1521-4095
VL  - 26
IS  - 16
SP  - 2533
EP  - 2539
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Albrecht, Steve
A1  - Tumbleston, John R.
A1  - Janietz, Silvia
A1  - Dumsch, Ines
A1  - Allard, Sybille
A1  - Scherf, Ullrich
A1  - Ade, Harald W.
A1  - Neher, Dieter
T1  - Quantifying charge extraction in organic solar cells: The case of fluorinated PCPDTBT
JF  - The journal of physical chemistry letters
N2  - We introduce a new and simple method to quantify the effective extraction mobility in organic solar cells at low electric fields and charge carrier densities comparable to operation conditions under one sun illumination. By comparing steady-state carrier densities at constant illumination intensity and under open-circuit conditions, the gradient of the quasi-Fermi potential driving the current is estimated as a function of external bias and charge density. These properties are then related to the respective steady-state current to determine the effective extraction mobility. The new technique is applied to different derivatives of the well-known low-band-gap polymer PCPDTBT blended with PC70BM. We show that the slower average extraction due to lower mobility accounts for the moderate fill factor when solar cells are fabricated with mono- or difluorinated PCPDTBT. This lower extraction competes with improved generation and reduced nongeminate recombination, rendering the monofluorinated derivative the most efficient donor polymer.
Y1  - 2014
U6  - https://doi.org/10.1021/jz500457b
SN  - 1948-7185
VL  - 5
IS  - 7
SP  - 1131
EP  - 1138
PB  - American Chemical Society
CY  - Washington
ER  -