title: Influence of the Hole Transporting Layer on the Thermal Stability of Inverted Organic Photovoltaics Using Accelerated-Heat Lifetime Protocols.
abstract: High power conversion efficiency (PCE) inverted organic photovoltaics (OPVs) usually use thermally evaporated MoO3as a hole transporting layer (HTL). Despite the high PCE values reported, stability investigations are still limited and the exact degradation mechanisms of inverted OPVs using thermally evaporated MoO3HTL remain unclear under different environmental stress factors. In this study, we monitor the accelerated lifetime performance under the ISOS-D-2 protocol (heat conditions 65 °C) of nonencapsulated inverted OPVs based on the thiophene-based active layer materials poly(3-hexylthiophene) (P3HT), poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), and thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTTT) blended with [6,6]-phenyl C71-butyric acid methyl ester (PC[70]BM). The presented investigation of degradation mechanisms focus on optimized P3HT:PC[70]BM-based inverted OPVs. Specifically, we present a systematic study on the thermal stability of inverted P3HT:PC[70]BM OPVs using solution-processed poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and evaporated MoO3HTL. Using a series of measurements and reverse engineering methods, we report that the P3HT:PC[70]BM/MoO3interface is the main origin of failure of the P3HT:PC[70]BM-based inverted OPVs under intense heat conditions, a trend that is also observed for the other two thiophene-based polymers used in this study.
authors.affiliation: Molecular Electronics and Photonics Research Unit, Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology , 3041 Limassol, Cyprus.
authors.forename: Felix
authors.initials: F
authors.lastname: Hermerschmidt
authors.affiliation: Molecular Electronics and Photonics Research Unit, Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology , 3041 Limassol, Cyprus.
authors.forename: Achilleas
authors.initials: A
authors.lastname: Savva
authors.affiliation: Molecular Electronics and Photonics Research Unit, Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology , 3041 Limassol, Cyprus.
authors.forename: Efthymios
authors.initials: E
authors.lastname: Georgiou
authors.forename: Sachetan M
authors.initials: SM
authors.lastname: Tuladhar
authors.forename: James R
authors.identifier: http://orcid.org/0000-0001-8353-7345
authors.initials: JR
authors.lastname: Durrant
authors.forename: Iain
authors.identifier: http://orcid.org/0000-0002-6340-7217
authors.initials: I
authors.lastname: McCulloch
authors.affiliation: Departments of Engineering Science and Physics, Division of Mathematical, Physical and Life Sciences, University of Oxford , Oxford OX1 3PD, U.K.
authors.forename: Donal D C
authors.initials: DDC
authors.lastname: Bradley
authors.affiliation: Institute for Materials in Electronics and Energy Technology, Friedrich-Alexander University Erlangen-Nuremberg , 91054 Erlangen, Germany.
authors.forename: Christoph J
authors.initials: CJ
authors.lastname: Brabec
authors.forename: Jenny
authors.initials: J
authors.lastname: Nelson
authors.affiliation: Molecular Electronics and Photonics Research Unit, Department of Mechanical Engineering and Materials Science and Engineering, Cyprus University of Technology , 3041 Limassol, Cyprus.
authors.forename: Stelios A
authors.identifier: http://orcid.org/0000-0002-7899-6296
authors.initials: SA
authors.lastname: Choulis
keywords: ISOS-D-2 protocol; buffer layer engineering; degradation mechanism; hole-transporting layer; inverted structure; lifetime; organic photovoltaics; thermal stability