TiO2 nanotube formation by Ti film anodization and their transport properties for dye-sensitized solar cells

In this paper, we present the synthesis of TiO2 nanotube (NT) arrays formed by anodization of Ti film deposited on a fluorine-doped tin oxide-coated glass substrate by direct current magnetron sputtering. NH4F/ethylene glycol electrolyte was used to demonstrate the growth of stable nanotubes at room temperature. TiO2 NTs as long as 4.8 ?m with the high expansion factor to the initial sputtered Ti film (2 ?m) were obtained, showing little undesired dissolution of the metal in the electrolyte during anodization. The average pore size and wall thickness of NTs were about 70 and 30 nm, respectively. Structural investigations on the transparent NT arrays reveal the presence of anatase phase after annealing. The NTs were sensitized by the N719 complex and the resultant photoelectrodes were incorporated into dye sensitized solar cells (DSSCs). The conversion efficiency of 1.97 % was obtained under AM 1.5 illumination and the open circuit voltage, short circuit current density and the fill factor were 0.59 V, 6.71 mA/cm2 and 0.50, respectively. Investigation of the electron transport of the DSSCs by electrochemical impedance spectroscopy showed that the electron diffusion length (8.6 ?m) was higher than NTs’ height. It was also observed that the electron transport resistance measured in NT DSSC was lower compared to the reported TiO2 nanoparticle one.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc

Highly selective and responsive ultra-violet detection using an improved phototransistor

An ultra-violet (UV) phototransistor with 700x200 lm2 gate area decorated with vertically aligned Zinc Oxide (ZnO) nanorods to enhance UV responsivity is designed and manufactured. Spectral responsivity of the device was measured for wavelengths ranged from 200 to 1100 nm of the electromagnetic spectrum in different transistor working regions. The best responsivity was achieved at sub-threshold and very weak inversion region. In order to enhance UV range selectivity, oxygen plasma has been employed on the nanorods, and consequently, nearly 3-fold improvement in its relative sensitivity at 375 nm was achieved. The final manufactured phototransistor shows a highly selective response of 24 kA/W in the UV range.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc

Monolithically Integrated Light Feedback Control Circuit for Blue/UV LED Smart Package

Given the performance decay of high-power light-emitting diode (LED) chips over time and package condition changes, having a reliable output light for sensitive applications is a point of concern. In this study, a light feedback control circuit, including blue-selective photodiodes, for blue/ultraviolet (UV) LED, has been designed and implemented using a low-cost seven-mask BiCMOS process. The feedback circuit was monolithically integrated in a package with four high-power blue LED chips. For sensing the intensity of exact colored blue/UV light in the package, selective photodiodes at 480-nm wavelength were implemented. An opamp-based feedback circuit combined with a high-power transistor controls the output light based on real-time sensor data. The whole system is a low-cost integrated package that guarantees a stable and reliable output light under different working conditions. Output light can be also controlled linearly by a reference input voltage.Electronic Components, Technology and MaterialsElectronic