Patrick Görrn

MoO3 Films Spin‐Coated from a Nanoparticle Suspension for Efficient Hole‐Injection in Organic Electronics

MoO3 films spin-coated from a suspension of nanoparticles, which offers energetic properties nearly identical to those of thermally evaporated MoO3 films, are reported. It is demonstrated that our solution-based MoO3 acts as a very efficient hole-injection layer for organic devices.

Stability of transparent zinc tin oxide transistors under bias stress

Shifts in the threshold voltage (ΔVth) of transparent zinc tin oxide (ZTO) transistors under gate bias stress are studied. The effect of composition and processing temperature on the device stability has been investigated. Based on the research, highly stable transistors with ΔVth as small as 30mV after 1000min of operation have been fabricated with a composition of [Zn]:[Sn]=36:64. As current drivers in active matrix displays their stability renders ZTO thin film transistors (TFTs) a very attractive alternative to TFTs based on established technologies.

The influence of visible light on transparent zinc tin oxide thin film transistors

The characteristics of transparent zinc tin oxide thin film transistors (TTFTs) upon illumination with visible light are reported. Generally, a reversible decrease of threshold voltage Vth, saturation field effect mobility μsat, and an increase of the off current are found. The time scale of the recovery in the dark is governed by the persistent photoconductivity in the semiconductor. Devices with tuned [Zn]:[Sn] ratio show a shift of Vth of less 2V upon illumination at 5mW∕cm2 (brightness >30000cd∕m2) throughout the visible spectrum. These results demonstrate TTFTs which are candidates as pixel drivers in transparent active-matrix organic light emitting diode displays.

Indium-free transparent organic light emitting diodes with Al doped ZnO electrodes grown by atomic layer and pulsed laser deposition

We present highly efficient transparent organic light emitting diodes (OLEDs) with Al doped ZnO (AZO) electrodes prepared by atomic layer deposition and pulsed laser deposition (PLD). The power and current efficiencies exceed 27 lm/W and 44 cd/A at a brightness level of 100 cd/m2, respectively. At the same time, the transmissivity of the devices is above 73% in the visible part of the spectrum. Owing to an efficient WO3 buffer layer and an optimized PLD process for the deposition of the top AZO electrode, the OLEDs show leakage current densities as low as 3×10−5 mA/cm2 at a reverse bias of 6 V. Therefore, our study paves the way for indium-free, see-through OLED displays.

Elastically tunable self-organized organic lasers.

Dr. P. Gorrn, Prof. S. WagnerDepartment of Electrical Engineering and Princeton Institute for the Science and Technology of Materials Princeton University, Princeton, NJ, 08544, USA E-mail: pgoerrn@princeton.eduM. Lehnhardt, Prof. W. KowalskyInstitut fur Hochfrequenztechnik TU Braunschweig, Schleinitzstr. 22, D-38106 Braunschweig, GermanyProf. T. RiedlInstitute of Electronic Devices University of Wuppertal Rainer-Gruenter-Str. 21, D-42119, Germany

Controlling the Morphology of Gold Films on Poly(dimethylsiloxane)

Gold films on poly(dimethylsiloxane) (PDMS) have applications in stretchable electronics, tunable diffraction gratings, soft lithography and as neural interfaces. The electrical and optical properties of these films depend critically on the morphology of the gold. Therefore, we examine qualitatively and quantitatively the factors that affect the morphology of the gold film. Three morphologies can be produced controllably: microcracked, buckled, and smooth. Which morphology a gold film will adopt depends on the film stress and the growth mode of the film. The factors that affect the film stress and growth mode, and thus the morphology, are as follows: deposition temperature, film thickness, elastic modulus, adhesion layer thickness, surface properties of the PDMS, and mechanical prestrain applied during deposition. We discuss how the different components of the film stress and growth mode of the film affect the morphology.

Transparent Electronics for See-Through AMOLED Displays

Transparent thin-film-transistors (TFTs) with a channel semiconductor based on the zinc-tin-oxide (ZTO) system are presented. Specifically, the technological and material aspects of the plasma-assisted pulsed laser deposition of these materials are discussed. The supply of additional radical oxygen species will be evidenced to significantly reduce defects in the material and as a consequence allows for well-behaved n-channel TFTs with mobilities higher than 10 cm2 V-1 s-1 and a threshold voltage in the range of 0 V. In addition the devices are extremely stable versus bias/current stress, which is especially important for active matrix OLED applications. Based on a detailed understanding of the interaction of the TFT channels with oxygen a strategy for the thin-film encapsulation of the TFTs will be presented, which leaves their device characteristics unaffected.

Highly Robust Transparent and Conductive Gas Diffusion Barriers Based on Tin Oxide

Transparent and electrically conductive gas diffusion barriers are reported. Tin oxide (SnOx ) thin films grown by atomic layer deposition afford extremely low water vapor transmission rates (WVTR) on the order of 10(-6) g (m(2) day)(-1) , six orders of magnitude better than that established with ITO layers. The electrical conductivity of SnOx remains high under damp heat conditions (85 °C/85% relative humidity (RH)), while that of ZnO quickly degrades by more than five orders of magnitude.

Plasmonically sensitized metal-oxide electron extraction layers for organic solar cells

ZnO and TiOx are commonly used as electron extraction layers (EELs) in organic solar cells (OSCs). A general phenomenon of OSCs incorporating these metal-oxides is the requirement to illuminate the devices with UV light in order to improve device characteristics. This may cause severe problems if UV to VIS down-conversion is applied or if the UV spectral range (λ < 400 nm) is blocked to achieve an improved device lifetime. In this work, silver nanoparticles (AgNP) are used to plasmonically sensitize metal-oxide based EELs in the vicinity (1–20 nm) of the metal-oxide/organic interface. We evidence that plasmonically sensitized metal-oxide layers facilitate electron extraction and afford well-behaved highly efficient OSCs, even without the typical requirement of UV exposure. It is shown that in the plasmonically sensitized metal-oxides the illumination with visible light lowers the WF due to desorption of previously ionosorbed oxygen, in analogy to the process found in neat metal oxides upon UV exposure, only. As underlying mechanism the transfer of hot holes from the metal to the oxide upon illumination with hν < Eg is verified. The general applicability of this concept to most common metal-oxides (e.g. TiOx and ZnO) in combination with different photoactive organic materials is demonstrated.

Low loss contacts for organic semiconductor lasers

For the realization of electrically driven organic semiconductor lasers low loss contacts for charge injection are essential. The authors show that the addition of thin, highly transparent conducting layers (thickness on the order of 10–20nm) of aluminum doped zinc oxide to a planar waveguide structure formed by a 145nm thick polymer active layer leaves the threshold for the onset of amplified spontaneous emission almost unchanged. This finding paves the way towards electrically driven organic lasers without the need for unrealistically thick organic spacers to keep the waveguide mode away from the contacts.