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One of the substrate layouts for our organic solar cells
Credit: AFMD Group

Moritz Riede

Professor of Soft Functional Nanomaterials

Research theme

  • Photovoltaics and nanoscience

Sub department

  • Condensed Matter Physics

Research groups

  • Advanced Functional Materials and Devices (AFMD) Group
moritz.riede@physics.ox.ac.uk
Telephone: 01865 (2)72377 (office),01865 (2)82095 (lab)
  • About
  • Research
  • Teaching
  • Publications

Characterization of tandem organic solar cells comprising subcells of identical absorber material

Progress in Photovoltaics: Research and Applications 23:10 (2015) 1353-1356

Authors:

R Timmreck, K Leo, M Riede

Abstract:

Recently organic tandem solar cells with record efficiency had been shown comprising identical absorber materials in both subcells. Such structures pose new challenges for characterization. The standard test methods for measuring spectral response of tandem solar cells can not be applied. The standard procedures demand for different bias illumination during measuring spectral response allowing to select the subcell being current limiting. With subcells comprising identical absorber materials, thus having identical absorption spectra, such a selection is not trivial. In this paper, we show that with the help of detailed optical simulations of such tandem organic solar cells, their characterization is possible, and we apply the proposed method to a sample structure.
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Characterization of tandem organic solar cells comprising subcells of identical absorber material

Progress in Photovoltaics Research and Applications Wiley 23:10 (2015) 1353-1356

Authors:

R Timmreck, K Leo, M Riede
More details from the publisher

Experimental and theoretical study of phase separation in ZnPc:C60 blends

Organic Electronics: physics, materials, applications 27 (2015) 183-191

Authors:

T Mönch, TS Sherkar, LJ Anton Koster, P Friederich, M Riede, P Formanek, C Koerner, K Vandewal, W Wenzel, K Leo

Abstract:

© 2015 Published by Elsevier B.V.Understanding the relationship between the absorber layer microstructure and the power conversion efficiency is of paramount importance to further improve the efficiency of organic solar cells. Utilizing transmission electron microscopy (TEM), (photo-)conductive atomic force microscopy ((p)cAFM), 3D drift-diffusion simulations, and density functional theory, we reveal the microscopic origins of phase-separation in a blend of zinc phthalocyanine (ZnPc) and C60, used as an absorber layer in organic solar cells. By means of (p)cAFM, we observe photoconductive, circular structures at the surface, which are identified as α-ZnPc islands. Moreover, in agreement with TEM investigations, we observe photoconductive, nanorod-like structures close to the surface which we assign to β-ZnPc. Finally, we apply a 3D drift-diffusion simulation based on the morphology determined by TEM to provide a link between the different contrasts observed in pcAFM and TEM.
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Characterization of tandem organic solar cells

Nature Photonics Nature Publishing Group 9 (2015) 478-479

Authors:

R Timmreck, T Meyer, J Gilot, H Seifert, T Mueller, A Furlan, MM Wienk, D Wynands, J Hohl-Ebinger, W Warta, RAJ Janssen, Moritz Riede, K Leo
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Enhanced Amplified Spontaneous Emission in Perovskites Using a Flexible Cholesteric Liquid Crystal Reflector.

Nano Letters 15:8 (2015) 4935-4941

Authors:

SD Stranks, SM Wood, K Wojciechowski, F Deschler, M Saliba, H Khandelwal, JB Patel, SJ Elston, LM Herz, MB Johnston, AP Schenning, MG Debije, MK Riede, SM Morris, HJ Snaith

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.
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