Extended Intermolecular Interactions Governing Photocurrent-Voltage Relations in Ternary Organic Solar Cells.
Efficient organic solar cells are based on (electron) donor-acceptor heterojunctions. An optically generated excited molecular state (exciton) is dissociated at this junction, forming a charge-transfer (CT) state in an intermediate step before the electron and hole are completely separated. The observed highly efficient dissociation of this Coulombically bound state raises the question on the dissociation mechanism. Here, we show that the observed high quantum yields of charge carrier generation and CT state dissociation are due to extended (and consequently weakly bound) CT states visible in absorption and emission spectra and first-principles calculations. Identifying a new geminate-pair loss mechanism via donor excimers, we find that the hole on the small-molecule donor is not localized on a single molecule and charge separation is correlated with the energetic offset between excimer and CT states. Thus, the charges upon interface charge transfer and even in the case of back-transfer and recombination are less localized than commonly assumed.
Biomolecular and Organic Electronics, IFM, Linköping University , 58183 Linköping, Sweden.
Wolfgang
W
Tress
Fraunhofer Institute for Electron Beam, Plasma Technology and COMEDD (FEP) , Maria-Reiche-Strasse 2, 01109 Dresden, Germany.
Beatrice
B
Beyer
Laboratoire de chimie et biochimie computationnelles, ISIC, FSB-BCH, École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
Negar
N
Ashari Astani
Biomolecular and Organic Electronics, IFM, Linköping University , 58183 Linköping, Sweden.
Feng
F
Gao
Laboratoire de chimie et biochimie computationnelles, ISIC, FSB-BCH, École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
Simone
S
Meloni
Laboratoire de chimie et biochimie computationnelles, ISIC, FSB-BCH, École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
Ursula
U
Rothlisberger