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Utilising energy transfer in binary and ternary bulk heterojunction organic solar cells Krishna Feron, James M Cave, Mahir Noori Thameel, Connor O'Sullivan, Renee Kroon, Mats R. Andersson, Xiaojing Zhou, Christopher James Fell, Warwick J. Belcher, Alison B. Walker, and Paul C. Dastoor ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05474 • Publication Date (Web): 26 Jul 2016 Downloaded from http://pubs.acs.org on July 27, 2016
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ACS Applied Materials & Interfaces
Utilising energy transfer in binary and ternary bulk heterojunction organic solar cells
Krishna Ferona,b,*, James M. Cavec, Mahir N. Thameelb,d, Connor O’Sullivanb, Renee Kroone,f, Mats R. Anderssone,f, Xiaojing Zhoub, Christopher J. Fella, Warwick J. Belcherb, Alison B. Walkerc, Paul C. Dastoorb a
CSIRO Energy, Newcastle, NSW 2300, Australia
b
Centre for Organic Electronics, University of Newcastle, University Drive, Callaghan, NSW,
2308, Australia c
Department of Physics, University of Bath, Bath BA2 7AY, United Kingdom
d
Department of Physics, College of education for pure science, University of Anbar, Iraq
e
Future Industries Institute, University of South Australia, Mawson Lakes Campus, SA 5095,
Australia f
Department of Chemistry and Chemical Engineering/Polymer Technology, Chalmers University of
Technology, 41296 Göteborg, Sweden *Corresponding author, e-mail:
[email protected] Abstract Energy transfer has been identified as an important process in ternary organic solar cells. Here, we develop kinetic Monte Carlo (KMC) models to assess the impact of energy transfer in ternary and binary bulk heterojunction systems. We used fluorescence and absorption spectroscopy to determine the energy disorder and Förster radii for poly(3-hexylthiophene-2,5-diyl), [6,6]-Phenyl-C61-butyric acid methyl ester, 4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (DIBSq) and poly(2,5-thiophene-alt-4,9-bis(2-hexyldecyl)-4,9-dihydrodithieno[3,2-c:3′,2′-h][1,5]naphthyridine5,10-dione). Hetero-energy transfer is found to be crucial in the exciton dissociation process of both binary and ternary organic semiconductor systems. Circumstances favouring energy transfer across
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interfaces allow relaxation of the electronic energy level requirements, meaning that a cascade structure is not required for efficient ternary organic solar cells. We explain how energy transfer can be exploited to eliminate additional energy losses in ternary bulk heterojunction solar cells, thus increasing their open-circuit voltage without loss in short-circuit current. In particular, we show that it is important that the DIBSq is located at the electron donor/acceptor interface, otherwise charge carriers will be trapped in the DIBSq domain or excitons in the DIBSq domains will not be able to dissociate efficiently at an interface. KMC modelling shows that only small amounts of DIBSq (
