Advanced Functional Materials and Devices (AFMD) Group

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.

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.

Abstract:

Thin metal films are a desirable alternative to indium tin oxide for utilization in organic solar cells (OSC).We describe background and processing parameters for thin metal films and show examples of top-illuminated OSC employing metal electrodes. Simulations are introduced as tool for OSC fabrication; several pitfalls are presented which must be considered for successful numerical treatment of thin-film layers at coalescence thicknesses and for coherent treatment. © 2009 SPIE.