Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 25, Issue 21, Pages 3164-3171Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201500500
Keywords
dipoles; surface potential; ultraviolet photoelectron spectroscopy; vacuum level
Categories
Funding
- National Science Fund for Distinguished Young Scholars [51425304]
- National Natural Science Foundation of China [51273088, 51263016, 51473075]
- National Basic Research Program of China (973 Program) [2014CB260409]
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Spin-coated film of poly(vinylidenefluoride-hexafluoropropylene) (P(VDF-HFP)) acts as a cathode/anode buffer layer in polymer solar cells (PSCs) with conventional/inverted device structures. Such devices show optimized performances comparable with the controlled device, making P(VDF-HFP) a good substitute for LiF/MoO3 as a cathode/anode buffer layer. Ultraviolet photoelectron spectroscopy (UPS) and Kelvin force microscope (KFM) measurements show that increased surface potential of active layers improves cathode contact. In piezoresponse force microscopy (PFM) measurement, P(VDF-HFP) responds to applied bias in phase curve, showing tunable dipole. This tunable dipole renders surface potential under applied bias. As a result, open-circuit voltage of devices alters instantly with poling voltage. Moreover, positive poling of P(VDF-HFP) together with simultaneous oxidation of Ag gradually improves performance of inverted structure device. Integer charge transfer (ICT) model elucidates improved electrode contacts by dipole tuning, varying surface potential and vacuum level shift. Understanding the function of dipole makes P(VDF-HFP) a promising and versatile buffer layer for PSCs.
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