Intercalated vs Non-Intercalated Morphologies in Donor-Acceptor Bulk Heterojunction Solar Cells: PBTTT:Fullerene Charge Generation and Recombination Revisited
AuthorsCollado Fregoso, Elisa
Hood, Samantha N.
Schroeder, Bob C.
Durrant, James R.
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
Chemical Science Program
KAUST Solar Center (KSC)
KSC, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
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AbstractIn this contribution, we study the role of the donor:acceptor interface nanostructure upon charge separation and recombination in organic photovoltaic devices and blend films, using mixtures of PBTTT and two different fullerene derivatives (PC70BM and ICTA) as models for intercalated and non-intercalated morphologies, respectively. Thermodynamic simulations show that while the completely intercalated system exhibits a large free-energy barrier for charge separation, this barrier is significantly lower in the non-intercalated system, and almost vanishes when energetic disorder is included in the model. Despite these differences, both fs-resolved transient absorption spectroscopy (TAS) and TDCF exhibit extensive first-order losses in that system, suggesting that geminate pairs are the primary product of photoexcitation. In contrast, the system that comprises a combination of fully intercalated polymer:fullerene areas and fullerene aggregated domains (1:4 PBTTT:PC70BM), is the only one that shows slow, second-order recombination of free charges, resulting in devices with an overall higher short circuit current and fill factor. This study therefore provides a novel consideration of the role of the interfacial nanostructure and the nature of bound charges, and their impact upon charge generation and recombination.
CitationCollado Fregoso E, Hood SN, Shoaee S, Schroeder BC, McCulloch I, et al. (2017) Intercalated vs Non-Intercalated Morphologies in Donor-Acceptor Bulk Heterojunction Solar Cells: PBTTT:Fullerene Charge Generation and Recombination Revisited. The Journal of Physical Chemistry Letters. Available: http://dx.doi.org/10.1021/acs.jpclett.7b01571.
SponsorsThis work was funded by UNVEiL, a BMBF project, the EPSRC (EP/IO1927B/1, EP/M023532/1 and EP/K011987/1) and the Welsh Assembly Government Sêr Cymru programme. ECF thanks CONACyT (scholarship 309929) and the Kernahan Fund from Imperial College London for funding. SNH and IK were supported by the Westpac Bicentennial Foundation and by the Australian Research Council through a Discovery Early Career Researcher Award (DE140100433) and through the Centre of Excellence for Engineered Quantum Systems (CE110001013).
PublisherAmerican Chemical Society (ACS)
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