Improved photon harvesting by employing C70 in bulk heterojunction solar cells

Proceedings of SPIE - The International Society for Optical Engineering 7725 (2010)

Authors:

S Pfuetzner, J Meiss, S Olthof, MP Hein, A Petrich, K Leo, M Riede, L Dunsch

Abstract:

To achieve higher efficiencies in organic solar cells, ideally the open circuit voltage (V), fill factor (FF) as well as the short current density (J) have to be further improved. However, only a few suitable acceptor molecules, e.g. C, are currently available for the photoactive layer. Despite a good electron mobility on the order of 1×10 cm/Vs the absorption of C in the visible sun spectrum is low. From polymer based solar cells it is known that the fullerene derivative [70]PCBM used in the photoactive layer shows a significant enhancement in J compared to [60]PCBM. This work investigates the application of fullerene C as acceptor in comparison to the well known C in vacuum processed small molecule solar cells. C shows a broadened and red shifted absorption (abs. maximum around 500 nm) compared to C. By fabricating p-i-i solar cells we show that the stronger absorption of C leads to enhanced photon harvesting and increased external quantum efficiency. The bulk heterojunction p-i-i solar cell containing C as acceptor and ZnPc as donor, co-evaporated with an optimized ratio of 2:1, and a layer thickness of 30 nm shows improved solar cell parameters: a 30% larger photocurrent of 10.1 mA/cm is obtained. The V of 0.56 V and FF of 55% remain comparable to C-containing p-i-i solar cells. Therefore, the solar cell performance is mainly improved by J and leads to a mismatch corrected power conversion efficiency of 3.12%. Thus, we show that C is an alternative fullerene to C for solar cell applications. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Light Incoupling & Optical Optimisation of Organic Solar Cells

Optica Publishing Group (2010) pwd5

Authors:

Jan Meiss, Rico Schueppel, Ronny Timmreck, Mauro Furno, Christian Uhrich, Stefan Sonntag, Wolf-Michael Gnehr, Martin Pfeiffer, Karl Leo, Moritz Riede

Verantwortung der Wissenschaftler gegenüber der Gesellschaft

Chapter in Gerechtigkeit und Verantwortung in der Klima- und Energiepolitik, MV-Verlag (2010)

Authors:

M Riede, U Wunderle

Efficient semitransparent small-molecule organic solar cells

Applied Physics Letters 95:21 (2009)

Authors:

J Meiss, K Leo, MK Riede, C Uhrich, WM Gnehr, S Sonntag, M Pfeiffer

Abstract:

We present semitransparent small-molecule organic solar cells (OSC) deposited by thermal evaporation onto indium tin oxide (ITO)-coated glass substrates. The devices employ ITO-free ultrathin metal layers as top electrodes, containing 1 nm metal surfactant interlayer for improved morphology. Using a bulk heterojunction of zinc phthalocyanine and C60, sandwiched in between doped dedicated transport layers for efficient charge carrier extraction, power conversion efficiencies comparable to conventional OSC with an intransparent thick back electrode and similar device layout are achieved: the semitransparent OSC yield power conversion efficiencies well above 2% with external quantum efficiencies above 30%-40%. Organic light incoupling layers improve the transmission to up to 50% in the visible part of the optical spectrum. © 2009 American Institute of Physics.

Characterization of effective charge carrier mobility in ZnPc/C60 solar cells after ageing

Physica Status Solidi (C) Current Topics in Solid State Physics 6:12 (2009) 2864-2866

Authors:

V Kažukauskas, A Arlauskas, M Pranaitis, R Lessmann, M Riede, K Leo

Abstract:

We have investigated the ageing of ZnPc/C60 solar cells in terms of changes of the charge carrier mobility and potential barrier height. The initial fast degradation of device performance within several hours was followed by a much slower one. The mobility decreases during degradation by about 30 to 50 %. Moreover, an increase of the effective barrier height at ZnPC/C60 interface from ∼0.55 eV up to ∼0.65 eV was observed. Meanwhile thermal activation energy values of the electrical conductivity grew from about 0.28 eV to about 0.34 eV after ageing. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.