Volume 24, Issue 1

The article presents an overview of polymeric materials for flexible substrates in photovoltaic (PV) structures that could be used as power supply in the personal electronic systems. Four types of polymers have been elected for testing. The first two are the most specialized and heat resistant polyimide films. The third material is transparent polyethylene terephthalate film from the group of polyesters which was proposed as a cheap and commercially available substrate for the technology of photovoltaic cells in a superstrate configuration. The last selected polymeric material is a polysiloxane, which meets the criteria of high elasticity, is temperature resistant and it is also characterized by relatively high transparency in the visible light range. For the most promising of these materials additional studies were performed in order to select those of them which represent the best optical, mechanical and temperature parameters according to their usage for flexible substrates in solar cells.

Dye-sensitized solar cells (DSSCs) were prepared using various food dyes. Food dyes are economically superior to organometallic dyes since they are nontoxic and inexpensive. The spectrophotometric evaluation of chosen food dyes in solution and on a TiO 2 substrate show that the dyes form J-aggregation on the photoelectrode substrate. Oxidation of potential measurements for used food dyes ensured an energetically permissible and thermodynamically favorable charge transfer throughout the continuous cycle of a photo-electric conversion. The performance of dye-sensitized solar cells based on food dyes was studied. The results illustrate that the dye containing carboxylic acid and sulfonic acid as the acceptor group gave the maximum conversion efficiency 4.20%.

In this paper an analysis of the surface properties of (Ti,Pd,Eu)O x thin films prepared by magnetron sputtering has been described. In particular, the results of composition and structure investigations were studied in relation to the surface state and optical properties. It was found that (Ti,Pd,Eu)O x film was nanocrystalline and had a rutile structure. The average crystallites size was equal to 7.8 nm. Films were homogeneous and had densely packed grains. Investigation of the surface properties by XPS showed that titanium was present at 4+ state (in the TiO 2 form), palladium occurred as PdO 2 (also at 4+ state), while europium was in Eu 2 O 3 form (at 3+ state). In comparison with the unmodified TiO 2 , the coating with Pd and Eu additives had a rather high transparency (approx. 47%) in the visible light range, its optical absorption edge was shifted towards into the longer wavelengths (from 345 nm to 452 nm), and the width of optical energy gap Egopt was nearly twice lower (1.82 eV). Besides, the resistivity of (Ti,Pd,Eu)O x at room temperature was 1x10 3 Wcm. In the case of the film as-deposited on Si substrate (p-type) the generation of photocurrent as a response to light beam excitation (λ exc = 527 nm) was observed.

In recent years, GaN-based light-emitting diode (LED) has been widely used in various applications, such as RGB lighting system, full-colour display and visible-light communication. However, the internal quantum efficiency (IQE) of green LEDs is significantly lower than that of other visible spectrum LED. This phenomenon is called “green gap”. This paper briefly describes the physical mechanism of the low IQE for InGaN/GaN multiple quantum well (MQW) green LED at first. The IQE of green LED is limited by the defects and the internal electric field in MQW. Subsequently, we discuss the recent progress in improving the IQE of green LED in detail. These strategies can be divided into two categories. Some of these methods were proposed to enhance crystal quality of InGaN/GaN MQW with high In composition and low density of defects by modifying the growth conditions. Other methods focused on increasing electron-hole wave function overlap by eliminating the polarization effect.

We demonstrate the generation of a near-diffraction-limited beam in a diode-side-pumped Nd:YAG slab laser with a nonreciprocal, self-adaptive cavity. The energy output of 228 mJ with 17.2% slope efficiency and 17.3% optical-to-optical efficiency was obtained.

Effect of doping and other device parameters on inter sub-band transition in the well, responsivity and dark current of GaAs/Al x Ga 1−x As quantum well infrared photodetector (QWIP) is investigated using theoretical model. 2X2 Hamiltonian method is used to calculate Eigen energy states in this modelling. Results show that peak absorption, responsivity and spectral broadening width increase nonlinearly with increasing doping concentration in the well. Peak absorption coefficient increases with increase in well width also. Moreover, with increase in mole fraction of Al in Al x Ga 1−x As barrier, the inter sub-band absorption is enhanced but, peak wavelength of absorption shifts towards shorter wavelengths. Dark current density depends on both, the doping concentration and applied bias.

Non-intentionally doped GaSb epilayers were grown by molecular beam epitaxy (MBE) on highly mismatched semi-insulating GaAs substrate (001) with 2 offcut towards [110]. The effects of substrate temperature and the Sb/Ga flux ratio on the crystalline quality, surface morphology and electrical properties were investigated by Nomarski optical microscopy, X-ray diffraction (XRD) and Hall measurements, respectively. Besides, differential Hall was used to investigate the hole concentration behaviour along the GaSb epilayer. It is found that the crystal quality, electrical properties and surface morphology are markedly dependent on the growth temperature and the group V/III flux ratio. Under the optimized parameters, we demonstrate a low hole concentration at very low growth temperature. Unfortunately, the layers grown at low temperature are characterized by wide FWHM and low Hall mobility.