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X-ray Microscopy of Photovoltaic Polyfluorene Blends: Relating Nanomorphology to Device Performance

Summary: X-ray Microscopy of Photovoltaic Polyfluorene Blends: Relating
Nanomorphology to Device Performance
Christopher R. McNeill,*, Benjamin Watts, Lars Thomsen,§ Harald Ade,
Neil C. Greenham, and Paul C. Dastoor§
CaVendish Laboratory, Department of Physics, UniVersity of Cambridge, J J Thomson AVenue,
Cambridge CB3 0HE, United Kingdom; Department of Physics, North Carolina State UniVersity,
Raleigh, North Carolina 27695; and School of Mathematical and Physical Sciences, UniVersity of
Newcastle, UniVersity DriVe, Callaghan NSW 2308, Australia
ReceiVed January 17, 2007; ReVised Manuscript ReceiVed February 23, 2007
ABSTRACT: The composition of blend films of poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,N-
phenyl-1,4-phenylenediamine) (PFB) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) used in prototype
polymer solar cells has been quantitatively mapped using scanning transmission X-ray microscopy (STXM). The
resolution of the STXM technique is 50 nm or better, allowing the first nanoscale lateral chemical mapping of
this blend system. For 1:1 blend films spin-coated from xylene we find that the F8BT-rich domain is over 90%
pure (by weight) and the PFB-rich domain contains 70% PFB. For 5:1 and 1:5 blend films processed from xylene,
the minority phases are found to be intermixed, containing as much as 50% by weight of the majority polymer.
Films prepared from chloroform with a 1:1 weight ratio have also been imaged but show no features on the
length scale of 50 nm or greater. Additionally, the performance of photovoltaic devices fabricated using films
prepared in an identical fashion to those prepared for STXM analysis has been evaluated and compared to the
performance of chloroform blends with varied weight ratio. By studying the influence of blend composition on


Source: Ade, Harald W.- Department of Physics, North Carolina State University


Collections: Physics