title: Protic ionic liquids as p-dopant for organic hole transporting materials and their application in high efficiency hybrid solar cells.
abstract: Chemical doping is a powerful method to improve the charge transport and to control the conductivity in organic semiconductors (OSs) for a wide range of electronic devices. We demonstrate protic ionic liquids (PILs) as effective p-dopant in both polymeric and small molecule OSs. In particular, we show that PILs promote single electron oxidation, which increases the hole concentration in the semiconducting film. The illustrated PIL-doping mechanism is compatible with materials processed by solution and is stable in air. We report the use of PIL-doping in hybrid solar cells based on triarylamine hole transporting materials, such as 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (spiro-OMeTAD). We show improved power conversion efficiency by replacing lithium salts, typical p-dopants for spiro-OMeTAD, with PILs. We use photovoltage-photocurrent decay and photoinduced absorption spectroscopy to establish that significantly improved device performance is mainly due to reduced charge transport resistance in the hole-transporting layer, as potentiated by PIL-doping.
authors.affiliation: Clarendon Laboratory, Department of Physics, University of Oxford , Parks Road, Oxford, OX1 3PU, United Kingdom.
authors.forename: Antonio
authors.initials: A
authors.lastname: Abate
authors.forename: Derek J
authors.initials: DJ
authors.lastname: Hollman
authors.forename: Joël
authors.initials: J
authors.lastname: Teuscher
authors.forename: Sandeep
authors.initials: S
authors.lastname: Pathak
authors.forename: Roberto
authors.initials: R
authors.lastname: Avolio
authors.forename: Gerardino
authors.initials: G
authors.lastname: D'Errico
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Vitiello
authors.forename: Simona
authors.initials: S
authors.lastname: Fantacci
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Snaith