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dc.contributor.authorThomson, Stuart
dc.contributor.authorNiklas, Jens
dc.contributor.authorMardis, Kirsty Lynn
dc.contributor.authorMallares, Christopher
dc.contributor.authorSamuel, Ifor D. W.
dc.contributor.authorPoluektov, Oleg G.
dc.identifier.citationThomson , S , Niklas , J , Mardis , K L , Mallares , C , Samuel , I D W & Poluektov , O G 2017 , ' Charge separation and triplet exciton formation pathways in small molecule solar cells as studied by time-resolved EPR spectroscopy ' , Journal of Physical Chemistry C , vol. 121 , no. 41 , pp. 22707-22719 .
dc.identifier.otherPURE: 250098697
dc.identifier.otherPURE UUID: f7ee505c-9508-4f03-a759-a2077f7cd262
dc.identifier.otherScopus: 85031900488
dc.identifier.otherWOS: 000413617900013
dc.descriptionFunding: EPSRC EP/G03673X/1 (SAJT), Royal Society Wolfson research merit award (IDWS).en
dc.description.abstractOrganic solar cells are a promising renewable energy technology, offering the advantages of mechanical flexibility and solution processability. An understanding of the electronic excited states and charge separation pathways in these systems is crucial if efficiencies are to be further improved. Here we use light induced electron paramagnetic resonance (LEPR) spectroscopy and density functional theory calculations (DFT) to study the electronic excited states, charge transfer (CT) dynamics and triplet exciton formation pathways in blends of the small molecule donors (DTS(FBTTh2)2, DTS(F2BTTh2)2, DTS(PTTh2)2, DTG(FBTTh2)2 and DTG(F2BTTh2)2) with the fullerene derivative PC61BM. Using high frequency EPR the g-tensor of the positive polaron on the donor molecules was determined. The experimental results are compared with DFT calculations which reveal that the spin density of the polaron is distributed over a dimer or trimer. Time-resolved EPR (TR-EPR) spectra attributed to singlet CT states were identified and the polarization patterns revealed similar charge separation dynamics in the four fluorobenzothiadiazole donors, while charge separation in the DTS(PTTh2)2 blend is slower. Using TR-EPR we also investigated the triplet exciton formation pathways in the blend. The polarization patterns reveal that the excitons originate from both intersystem crossing (ISC) and back electron transfer (BET) processes. The DTS(PTTh2)2 blend was found to contain substantially more triplet excitons formed by BET than the fluorobenzothiadiazole blends. The higher BET triplet exciton population in the DTS(PTTh2)2 blend is in accordance with the slower charge separation dynamics observed in this blend.
dc.relation.ispartofJournal of Physical Chemistry Cen
dc.rights© 2017 American Chemical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at
dc.subjectQC Physicsen
dc.subjectQD Chemistryen
dc.subjectSDG 7 - Affordable and Clean Energyen
dc.titleCharge separation and triplet exciton formation pathways in small molecule solar cells as studied by time-resolved EPR spectroscopyen
dc.typeJournal articleen
dc.contributor.sponsorThe Royal Societyen
dc.contributor.institutionUniversity of St Andrews. School of Physics and Astronomyen
dc.contributor.institutionUniversity of St Andrews. Condensed Matter Physicsen
dc.description.statusPeer revieweden

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