Note: Laser-cut molybdenum grids for a retarding field energy analyzer.

A retarding field energy analyzer (RFEA) with grids created by laser-cutting a honeycomb mesh in a 50 µm thick molybdenum foil is presented. The flat grids span an area of 1 cm2 and have high transmission (20 µm wide walls between 150 µm wide meshes). The molybdenum grids were tested in a 3-grid RFEA configuration with an analyzer depth of 0.87 mm.

Er(3+)/Yb(3+) upconverters for InGaP solar cells under concentrated broadband illumination.

The inability of solar cell materials to convert all incident photon energy into electrical current, provides a fundamental limit to the solar cell efficiency; the so called Shockley-Queisser (SQ) limit. A process termed upconversion provides a pathway to convert otherwise unabsorbed low energy photons passing through the solar cell into higher energy photons, which subsequently can be redirected back to the solar cell. The combination of a semi-transparent InGaP solar cell with lanthanide upconverters, consisting of ytterbium and erbium ions doped in three different host materials (Gd2O2S, Y2O3 and NaYF4) is investigated. Using sub-band gap light of wavelength range 890 nm to 1045 nm with a total accumulated power density of 2.7 kW m(-2), a distinct photocurrent was measured in the solar cell when the upconverters were applied whereas a zero current was measured without upconverter. Furthermore, a time delay between excitation and emission was observed for all upconverter systems which can be explained by energy transfer upconversion. Also, a quadratic dependence on the illumination intensity was observed for the NaYF4 and Y2O3 host material upconverters. The Gd2O2S host material upconverter deviated from the quadratic illumination intensity dependence towards linear behaviour, which can be attributed to saturation effects occurring at higher illumination power densities.

Switching CdSe quantum dot luminescence with a-Si:H.

Dynamical control of the luminescence of quantum dots is highly important for technology in the field of telecommunication, displays, and photovoltaics. In this work we use an a-Si:H solar cell structure in which CdSe quantum dots are sandwiched. By applying a positive potential over the device, charge carriers generated in the quantum dots are transported to the a-Si:H layer and transformed into electrical energy, changing the luminescence intensity with a switching time lower than 60 ms. This is a promising new step towards using quantum dots in optical switching devices.

Low temperature silicon nitride by hot wire chemical vapour deposition for the use in impermeable thin film encapsulation on flexible substrates.

High quality non porous silicon nitride layers were deposited by hot wire chemical vapour deposition at substrate temperatures lower than 110 degrees C. The layer properties were investigated using FTIR, reflection/transmission measurements and 1:6 buffered HF etching rate. A Si-H peak position of 2180 cm(-1) in the Fourier transform infrared absorption spectrum indicates a N/Si ratio around 1.2. Together with a refractive index of 1.97 at a wavelength of 632 nm and an extinction coefficient of 0.002 at 400 nm, this suggests that a transparent high density silicon nitride material has been made below 110 degrees C, which is compatible with polymer films and is expected to have a high impermeability. To confirm the compatibility with polymer films a silicon nitride layer was deposited on poly(glycidyl methacrylate) made by initiated chemical vapour deposition, resulting in a highly transparent double layer.