TY  - JOUR
A1  - Schubert, Marcel
A1  - Dolfen, Daniel
A1  - Frisch, Johannes
A1  - Roland, Steffen
A1  - Steyrleuthner, Robert
A1  - Stiller, Burkhard
A1  - Chen, Zhihua
A1  - Scherf, Ullrich
A1  - Koch, Norbert
A1  - Facchetti, Antonio
A1  - Neher, Dieter
T1  - Influence of aggregation on the performance of All-Polymer Solar Cells containing Low-Bandgap Naphthalenediimide Copolymers
JF  - dvanced energy materials
N2  - The authors present efficient all-polymer solar cells comprising two different low-bandgap naphthalenediimide (NDI)-based copolymers as acceptors and regioregular P3HT as the donor. It is shown that these naphthalene copolymers have a strong tendency to preaggregate in specific organic solvents, and that preaggregation can be completely suppressed when using suitable solvents with large and highly polarizable aromatic cores. Organic solar cells prepared from such nonaggregated polymer solutions show dramatically increased power conversion efficiencies of up to 1.4%, which is mainly due to a large increase of the short circuit current. In addition, optimized solar cells show remarkable high fill factors of up to 70%. The analysis of the blend absorbance spectra reveals a surprising anticorrelation between the degree of polymer aggregation in the solid P3HT:NDI copolymer blends and their photovoltaic performance. Scanning near-field optical microscopy (SNOM) and atomic force microscopy (AFM) measurements reveal important information on the blend morphology. It is shown that films with high degree of aggregation and low photocurrents exhibit large-scale phase-separation into rather pure donor and acceptor domains. It is proposed that, by suppressing the aggregation of NDI copolymers at the early stage of film formation, the intermixing of the donor and acceptor component is improved, thereby allowing efficient harvesting of photogenerated excitons at the donoracceptor heterojunction.
KW  - aggregation
KW  - morphology
KW  - naphthalenediimide
KW  - organic semiconductors
KW  - organic photovoltaics
Y1  - 2012
U6  - https://doi.org/10.1002/aenm.201100601
SN  - 1614-6832
VL  - 2
IS  - 3
SP  - 369
EP  - 380
PB  - Wiley-VCH
CY  - Weinheim
ER  -