TY  - JOUR
A1  - Sini, Gjergji
A1  - Schubert, Marcel
A1  - Risko, Chad
A1  - Roland, Steffen
A1  - Lee, Olivia P.
A1  - Chen, Zhihua
A1  - Richter, Thomas V.
A1  - Dolfen, Daniel
A1  - Coropceanu, Veaceslav
A1  - Ludwigs, Sabine
A1  - Scherf, Ullrich
A1  - Facchetti, Antonio
A1  - Frechet, Jean M. J.
A1  - Neher, Dieter
T1  - On the Molecular Origin of Charge Separation at the Donor-Acceptor Interface
JF  - Advanced energy materials
N2  - Fullerene-based acceptors have dominated organic solar cells for almost two decades. It is only within the last few years that alternative acceptors rival their dominance, introducing much more flexibility in the optoelectronic properties of these material blends. However, a fundamental physical understanding of the processes that drive charge separation at organic heterojunctions is still missing, but urgently needed to direct further material improvements. Here a combined experimental and theoretical approach is used to understand the intimate mechanisms by which molecular structure contributes to exciton dissociation, charge separation, and charge recombination at the donor-acceptor (D-A) interface. Model systems comprised of polythiophene-based donor and rylene diimide-based acceptor polymers are used and a detailed density functional theory (DFT) investigation is performed. The results point to the roles that geometric deformations and direct-contact intermolecular polarization play in establishing a driving force ( energy gradient) for the optoelectronic processes taking place at the interface. A substantial impact for this driving force is found to stem from polymer deformations at the interface, a finding that can clearly lead to new design approaches in the development of the next generation of conjugated polymers and small molecules.
KW  - donor-acceptor interfaces
KW  - energy gradients
KW  - geometrical deformations
KW  - nonfullerene acceptors
KW  - organic photovoltaics
KW  - photocurrent generation
KW  - polymer solar cells
Y1  - 2018
U6  - https://doi.org/10.1002/aenm.201702232
SN  - 1614-6832
SN  - 1614-6840
VL  - 8
IS  - 12
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Ran, Niva A.
A1  - Roland, Steffen
A1  - Love, John A.
A1  - Savikhin, Victoria
A1  - Takacs, Christopher J.
A1  - Fu, Yao-Tsung
A1  - Li, Hong
A1  - Coropceanu, Veaceslav
A1  - Liu, Xiaofeng
A1  - Bredas, Jean-Luc
A1  - Bazan, Guillermo C.
A1  - Toney, Michael F.
A1  - Neher, Dieter
A1  - Thuc-Quyen Nguyen, 
T1  - Impact of interfacial molecular orientation on radiative recombination and charge generation efficiency
JF  - Nature Communications
N2  - A long standing question in organic electronics concerns the effects of molecular orientation at donor/acceptor heterojunctions. Given a well-controlled donor/acceptor bilayer system, we uncover the genuine effects of molecular orientation on charge generation and recombination. These effects are studied through the point of view of photovoltaics-however, the results have important implications on the operation of all optoelectronic devices with donor/ acceptor interfaces, such as light emitting diodes and photodetectors. Our findings can be summarized by two points. First, devices with donor molecules face-on to the acceptor interface have a higher charge transfer state energy and less non-radiative recombination, resulting in larger open-circuit voltages and higher radiative efficiencies. Second, devices with donor molecules edge-on to the acceptor interface are more efficient at charge generation, attributed to smaller electronic coupling between the charge transfer states and the ground state, and lower activation energy for charge generation.
Y1  - 2017
U6  - https://doi.org/10.1038/s41467-017-00107-4
SN  - 2041-1723
VL  - 8
PB  - Nature Publ. Group
CY  - London
ER  -