title: Toward Improved Lifetimes of Organic Solar Cells under Thermal Stress: Substrate-Dependent Morphological Stability of PCDTBT:PCBM Films and Devices.
abstract: Morphological stability is a key requirement for outdoor operation of organic solar cells. We demonstrate that morphological stability and lifetime of polymer/fullerene based solar cells under thermal stress depend strongly on the substrate interface on which the active layer is deposited. In particular, we find that the stability of benchmark PCDTBT/PCBM solar cells under modest thermal stress is substantially increased in inverted solar cells employing a ZnO substrate compared to conventional devices employing a
  PSS substrate. This improved stability is observed to correlate with PCBM nucleation at the 50 nm scale, which is shown to be strongly influenced by different substrate interfaces. Employing this approach, we demonstrate remarkable thermal stability for inverted PCDTBT:PC70BM devices on ZnO substrates, with negligible (<2%) loss of power conversion efficiency over 160 h under 85 °C thermal stress and minimal thermally induced "burn-in" effect. We thus conclude that inverted organic solar cells, in addition to showing improved environmental stability against ambient humidity exposure as widely reported previously, can also demonstrate enhanced morphological stability. As such we show that the choice of suitable substrate interfaces may be a key factor in achieving prolonged lifetimes for organic solar cells under thermal stress conditions.
authors.affiliation: Department of Chemistry, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.|SPECIFIC, College of Engineering, Swansea University, Baglan Bay Innovation, Knowledge Centre, Central Avenue, Baglan SA12 7AX.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Chemistry, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.|Department of Chemical Engineering, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.
authors.forename: Kar
authors.initials: K
authors.lastname: Ho Chiu
authors.affiliation: Department of Chemistry, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.
authors.forename: Raja
authors.initials: R
authors.lastname: Shahid Ashraf
authors.affiliation: Department of Materials, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.
authors.forename: Sarah
authors.initials: S
authors.lastname: Fearn
authors.affiliation: Department of Chemical Engineering, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Dattani
authors.affiliation: Department of Chemical Engineering, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.|Engineering Product Development, Singapore University of Technology and Design, 8 Somapah Road, 487372 Singapore.
authors.forename: Him
authors.initials: H
authors.lastname: Cheng Wong
authors.affiliation: Department of Chemistry, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.|SPECIFIC, College of Engineering, Swansea University, Baglan Bay Innovation, Knowledge Centre, Central Avenue, Baglan SA12 7AX.
authors.forename: Ching-Hong
authors.initials: CH
authors.lastname: Tan
authors.affiliation: Department of Chemistry, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.
authors.forename: Jiaying
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Chemical Engineering, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.
authors.forename: João T
authors.initials: JT
authors.lastname: Cabral
authors.affiliation: Department of Chemistry, Centre for Plastic Electronics, Imperial College London, London SW7 2AZ.|SPECIFIC, College of Engineering, Swansea University, Baglan Bay Innovation, Knowledge Centre, Central Avenue, Baglan SA12 7AX.
authors.forename: James R
authors.initials: JR
authors.lastname: Durrant