Suppressing Energy Loss due to Triplet Exciton Formation in Organic Solar Cells: The Role of Chemical Structures and Molecular Packing

Abstract
In the most efficient solar cells based on blends of a conjugated polymer (electron donor) and a fullerene derivative (electron acceptor),ultrafast formation of charge-transfer (CT) electronic states at the donor-acceptor interfaces and efficient separation of these CT states into free charges, lead to internal quantum efficiencies near 100%. However, there occur substantial energy losses due to the non-radiative recombinations of the charges, mediated by the loweset-energy (singlet and triplet) CT states; for example, such recombinations can lead to the formation of triplet excited electronic states on the polymer chains, which do not generate free charges. This issue remains a major factor limiting the power conversion efficiencies (PCE) of these devices. The recombination rates are, however, difficult to quantify experimentally. To shed light on these issues, here, an integrated multi-scale theoretical approach that combines molecular dynamics simulations with quantum chemistry calculations is employed in order to establish the relationships among chemical structures, molecular packing, and non-radiative recombination losses mediated by the lowest-energy charge-transfer states.

Citation
Chen X-K, Wang T, Brédas J-L (2017) Suppressing Energy Loss due to Triplet Exciton Formation in Organic Solar Cells: The Role of Chemical Structures and Molecular Packing. Advanced Energy Materials: 1602713. Available: http://dx.doi.org/10.1002/aenm.201602713.

Acknowledgements
X.-K.C. and T.W. contributed equally to this work. This work was supported by competitive research funding at the King Abdullah University of Science and Technology (KAUST) and by the ONR Global, Grant N62909-15-1-2003. The authors acknowledge the KAUST IT Research Computing Team and Supercomputing Laboratory for providing precious continuous assistance as well as computational and storage resources.

Publisher
Wiley

Journal
Advanced Energy Materials

DOI
10.1002/aenm.201602713

Additional Links
http://onlinelibrary.wiley.com/doi/10.1002/aenm.201602713/full

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