title: Enhanced Amplified Spontaneous Emission in Perovskites Using a Flexible Cholesteric Liquid Crystal Reflector.
abstract: Organic-inorganic perovskites are highly promising solar cell materials with laboratory-based power conversion efficiencies already matching those of established thin film technologies. Their exceptional photovoltaic performance is in part attributed to the presence of efficient radiative recombination pathways, thereby opening up the possibility of efficient light-emitting devices. Here, we demonstrate optically pumped amplified spontaneous emission (ASE) at 780 nm from a 50 nm-thick film of CH3NH3PbI3 perovskite that is sandwiched within a cavity composed of a thin-film (∼7 μm) cholesteric liquid crystal (CLC) reflector and a metal back-reflector. The threshold fluence for ASE in the perovskite film is reduced by at least two orders of magnitude in the presence of the CLC reflector, which results in a factor of two reduction in threshold fluence compared to previous reports. We consider this to be due to improved coupling of the oblique and out-of-plane modes that are reflected into the bulk in addition to any contributions from cavity modes. Furthermore, we also demonstrate enhanced ASE on flexible reflectors and discuss how improvements in the quality factor and reflectivity of the CLC layers could lead to single-mode lasing using CLC reflectors. Our work opens up the possibility of fabricating widely wavelength-tunable "mirror-less" single-mode lasers on flexible substrates, which could find use in applications such as flexible displays and friend or foe identification.
authors.affiliation: †Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K.
authors.forename: Samuel D
authors.initials: SD
authors.lastname: Stranks
authors.affiliation: ‡Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, U.K.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Wood
authors.affiliation: †Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K.
authors.forename: Konrad
authors.initials: K
authors.lastname: Wojciechowski
authors.affiliation: §Cavendish Laboratory, University of Cambridge, J J Thomson Avenue, Cambridge CB3 0HE, U.K.
authors.forename: Felix
authors.initials: F
authors.lastname: Deschler
authors.affiliation: †Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K.
authors.forename: Michael
authors.initials: M
authors.lastname: Saliba
authors.affiliation: ⊥Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, Eindhoven, 5600 MB, The Netherlands.
authors.forename: Hitesh
authors.initials: H
authors.lastname: Khandelwal
authors.affiliation: †Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K.
authors.forename: Jay B
authors.initials: JB
authors.lastname: Patel
authors.affiliation: ‡Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, U.K.
authors.forename: Steve J
authors.initials: SJ
authors.lastname: Elston
authors.affiliation: †Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K.
authors.forename: Laura M
authors.initials: LM
authors.lastname: Herz
authors.affiliation: †Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Johnston
authors.affiliation: ⊥Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, Eindhoven, 5600 MB, The Netherlands.
authors.forename: Albertus P H J
authors.initials: AP
authors.lastname: Schenning
authors.affiliation: ⊥Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, Eindhoven, 5600 MB, The Netherlands.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Debije
authors.affiliation: †Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K.
authors.forename: Moritz K
authors.initials: MK
authors.lastname: Riede
authors.affiliation: ‡Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, U.K.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Morris
authors.affiliation: †Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, U.K.
authors.forename: Henry J
authors.initials: HJ
authors.lastname: Snaith
keywords: Organic−inorganic perovskite; amplified spontaneous emission; cholesteric liquid crystal; flexible; lasing; passivation; photoluminescence