restrict them from reaching significantly higher efficiencies. In order to further reduce transmission and thermalization losses, additional junctions are required. Increasing the number of junctions has diminishing returns as shown in Figure 1.4 where the maximum detailed balance efficiency for solar cells with one to seven junctions is shown, both under one sun and 500x AM1.5G concentration . The figure shows that as the number of junctions is increased the percent increase in efficiency with respect to the number of junctions decreases. The current generated in a multiple junction device will equal the sub-cell with the lowest current due to Kirchoff’s current law. When each of the sub-cells is current matched to the other sub-cells no excess current from an individual sub-cell is lost to heat and higher efficiencies can be achieved. Current matching is an increasingly difficult condition to meet as the number of sub-cells increases because the available semiconductors with a common lattice constant is limited as shown in Figure 1.5. Much recent work has demonstrated triple-junction devices with differing lattice constants grown through metamorphic buffer layers [18, 19, 20]; however, the efficiency is limited by defects formed due to strain . As a result, much current work is focused towards the development of a next generation design, the IBSC [22, 23].
The best front-side contacted solarcell, fabricated in this work, reaches a maximum efficiency of 23% at around 100 suns. The cell was processed on a 280 µm thick 0.5 Ωcm substrate. The front metal grid is 4 µm thick and square geometry. The finger distance of this cell is 180 µm. The optimized grid finger structure guarantees high fill factors, low series resistance and low surface shadowing also at high concentration levels. The front surface of this cell provides selective texturing (it means that only the area between the fingers is textured, while the finger itself lays on a planar sustain). This technique allows to reach very low reflectance and at the same time it preserves the integrity of the metal fingers, also when very narrow fingers (7 µm wide) with high aspect-ratio are used. The textured front side of these cells seems to be nearly perfect leading to very low reflection losses, very high light trapping and to very high short-circuit densities.
One of the leading examples of photovoltaic cell is CIS/CIGS based solarcell. CIS absorber layer having chalcopyrite crystal structure with optimal band gap 1.05 eV and high optical absorption coefficient ~10 5 /cm 2 suitable for high efficiency thin film solarcelldevelopment. It consist of elements from different group from the periodic table; Cu from Group I, In from Group III and Se from Group VI. The crystal structure of CuInSe 2 is shown in Figure 1. CIS and CIGS are
illumination. Also included are three 1 x 0.5 cm 2 concentrator-designed grid cells, two quantum efficiency pads, transmission line model (TLM) measurement pads A broadband/g-line ultraviolet light source was calibrated to 10 mW/cm 2 irradiance. A 12.5 second exposure provides an energy density (dose) of 125 mJ/cm 2 . A photoresist development step is then performed using MicroChem Microposit MF CD26 developer solution, after a Hexa-Methyl Disilizane (HMDS) surfactant surface preparation. After a two minute developer immersion (approximately 1 minute for the photoactive layer, and 1 minute for the development of the LOR resist), the wafers are rinsed with de-ionized water, and dried with a nitrogen jet. After the image is transferred into the photoresist pattern, An overhang sidewall profile remains due to the isotropic dissolution of the LOR resist. Thermally deposited metallization is then applied. To realize the grid structure and remove the underlying resist, a strong polar solvent, N-methyl Pyrrolidinone is used (Nano Remover PG by Microchem) for the removal of all photoresist, lifting off the metal of the negative image of the mask, leaving only the desired pattern. The annealing step is then performed described above.
Although there is still a large amount of crude oil, the principle question at present is no longer related to the time it will last but to the environmental damage it produces. The use of fossil fuels is frequently associated with several environmental effects such as greenhouse effect. This situation is worsening due to the increasing energy demand all over the world. These problems have stimulated the development of renewable energy sources such as solar energy. Nowadays, photovoltaic energy is mainly utilized using silicon based technology. Although this technology has reached highly developed stages, silicon based solar cells still present high costs of production because the materials must be extremely pure to ensure the efficiency of the devices produced. Thin film solar cells have been reported to be 40% cheaper than silicon solar cells (Imanzai et al., 2012). Thus there is an increasing interest in the development of alternative materials and technologies for solarcell energy conversion with minimal cost of production. ZnSe and Cu x O y are good candidates for
Producing high-efficiency and cheap solar cells has become an important goal of research. Therefore, SiNWs have acquired increasing attention for achieving the third generation solarcell, which would allow the reduction of device production and material costs, as well as for the development of the new generation of thin film Si solar cells with enhanced light trapping (Tsakalakos et al. 2007). Using Si nanowire array- based PV cells has great potential because of the proven track record of polycrystalline Si solar cells. In addition, Si nanowires have high absorbance of light because the band gap in SiNWs transforms from indirect into direct induced by the quantum confinement effect at the nanometre size (Feynman 1960; Honsberg et al. 2006).
Techniques more frequently used in the preparation of ZnS films include Spray Pyrolysis , electro deposition  and chemical bath deposition technique , among others. Recently more attention has been bestowed on the development of cost effective thin films deposited techniques, especially in the field of photovoltaic technology, for preparation of quality alternative window layers for devices over large areas in order to economize the technology. In view of this, a simple chemical bath deposition (CBD) technique is hereby investigated for the preparation of ZnS film. Low cost and simple apparatus were used to perform the deposition. This paper presents a study of the optical and electrical properties of the resulting ZnS thin films doped with tin.
The spectral response profile of the GaInNAs n-i-p-i solarcell was taken using the same experimental condi- tions, and it is shown in Figure 5. As expected, it extends to longer wavelengths of 1.1 μm corresponding to photon energies of approximately 1.1 eV. The drop- ping shape of the spectrum suggests that only the top layers contribute to the device current. This could be purely a fabrication problem which has no bearing in the material properties or the design. If the ion implants have not reached or been activated at the bottom layers, the device will collect carriers at the top layers (short wavelengths) while most of the carries at the bottom layers (long wavelengths) will recombine before reaching the vertical contacts, consequently leading to low short- circuit current density values. As a result, the device will behave like a thin cell which only absorbs shorter wave- length photons, and it is transparent to the longer wave- length ones. In relation with the J-V curve, our GaInNAs device had J sc = 4.2 mA/cm 2 and V oc = 0.19 V, as shown
electrode effectively. The wavelength-dependent com- plex refractive index used to describe the material dis- persion properties of GaAs can be obtained from the study of Levinshtein et al. . By applying periodic boundary conditions in the x and y directions, the simu- lations are carried out within this unit cell to model the periodic NWA structure. The simulation domain is closed at the top and bottom with a perfectly matched layer, allowing reflected light and transmission light to escape the simulation volume. The incident light from the top is set in parallel to the NW axis as indicated in Fig. 1a, and we use a plane wave defined with power intensity and wavelength values from a discretized AM 1.5G solar spectrum with a wavelength ranging from 290 to 900 nm (typical absorption region of GaAs) to model the sunlight. The reflection monitor is located at above the top surface of the NWA, and the transmission monitor is located at the bottom surface of substrate to calculate the light absorbed. The amount of power trans- mitted through the power monitors is normalized to the source power at each wavelength. The reflectance R (λ) and transmission T (λ) are calculated by the equation
Hybrid holographic solar concentrator operates in the following manner. Solar radiation of various wave- lengths runs through the upper plate 1 and then the layer 2 of the dye in the immersion liquid. Dye partially re-emits shorter wavelengths into the spectral region of absorption of the solar cells. When sunlight falls on the holographic grating, decomposed spectrum appears as a result of Bragg diffraction :
1=2 ; (3) where and are two free parameters and V cell is the unit cell volume. Minimization of the mean absolute relative error for the band gap of the solids listed in Table I leads to ¼ 0:012 (dimensionless) and ¼ 1:023 bohr 1=2 . Equation (1) was chosen such that the LDA exchange potential v LDA x; ¼ ð3=Þ 1=3 ð2 Þ 1=3 is approximately re-
Straightforward fix antennas can be coordinated with surface-mounted solar boards of little satellites  or window glass of structures or autos . These applications require high optical straightforwardness just as great radiation properties of the antenna. Fix antennas produced using straightforward conductive film, for example, silver covered polyester and indium tin oxides (ITO) films, were accounted for [1, 5]. Be that as it may, the straightforwardness of these antennas isn't sufficiently high for viable applications. Reports on coincided fix antennas recommended an unpredictable exchange off between the antenna's properties: the transfer speed and cross-polarization level can be improved by sacriﬁcing the increase ; a low radar cross segment (RCS) can be accomplished if the addition and transmission capacity are undermined .
A solarcell, which also known as photovoltaic cell is one of the promising options of renewable energy. A solarcell is a photonic device that converts photons with specific wavelengths to electricity. Solarcell is divided into two groups which are the crystalline silicon and thin film. The first and second generation of photovoltaic cells are mainly constructed from semiconductors including crystalline silicon, III-V compounds, cadmium telluride and copper indium selenide/sulfide . Th. dye-sensitized solar cells
Many solarcell technologies exist for the direct conversion of light into electricity, each with its own advantages and disadvantages. One of the most important metrics for determining the competitiveness of different solarcell technologies is the expected cost per watt produced. There are many strategies being pursued to achieve cost efficiency such as improving efficiency of standard silicon cells, reducing the amount of expensive raw materials with thin films, developing low cost manufacturing methods, and designing high-efficiency devices with small areas. Organic solar cells are a newer technology in this field and have the potential for low manufacturing and material costs. Many challenges still remain for moving organic solar cells from the laboratory into high-volume commercial applications. In particular, some of the needs in organics are a clearer understanding of the device physics, refinement of high- volume fabrication techniques, improvements in overall
Dr. Eman M. Nasir. Assistant Professor in Physics .She was born in Baghdad, Iraq. She had Ph.D in Thin Films Physics from University of Baghdad, College of Science in 2005. She published more than forty papers in the field of thin films, solar cells, Solid state physics ,Semiconductor detectors and characterization of optoelectronic devices.
Dye-sensitized solarcell (DSSC) is a new type of solarcell that attracted the attention from the researchers in all the world due to their low cost of production and environmental friendliness. DSSC was first developed by O’regan and Gratzel . Like other solar cells, the DSSCs are used for converting light energy into useable electricity. The first efficiency of DSSC reported is 7.1% . then efficiency of the DSSC has been improved to 11.5% .
ABSTRACT: -Solar energy is considered as the most promising alternative energy source to replace environmentally distractive fossil fuel. A solarcell, often called a photovoltaic (PV) cell, converts the energy in sunlight directly into electricity.. Photovoltaic, or PV, refers to the conversion of light energy into electricity using electronic devices called solar cells. Solarcell is Unlike silicon-wafer cells, which have light-absorbing layers that are traditionally 350 microns thick, thin-film solar cells have light-absorbing layers that are just one micron thick. A micron, for reference, is one-millionth of a meter (1/1,000,000 m or 1 µm). The most common thin-film semiconductor materials are cadmium telluride (CdTe), amorphous silicon (a-Si), and alloys of copper indium gallium diselenide (CIGS). The semiconductor layer is typically deposited on a substrate or superstrate inside a vacuum chamber. A number of companies are pursuing lower-cost, non-vacuum approaches for manufacturing thin-film materials. This paper analysis both the features of CIGS and CdTe base on long-term stable performance and potential for low-cost production.
A CdO/Si solarcell was fabricated via deposition of a CdO thin film on p-type silicon substrate at room temperature by thermal evaporation technique for CdO powder in a vacuum (2.2 10 5 mbar). The synthesized thin film has a thickness of approximately 346 nm. Scanning electron microscopy revealed that the thin film had a good quality structure. X-ray diffraction and energy dispersive X-ray analysis were used to characterize the structural properties of the solarcell. The CdO thin film had a grain size of 34 nm. The solarcell yielded a minimum effective reflectance that exhibited excellent light-trapping at wavelengths ranging from 400 nm to 1000 nm. Photoluminescence spectroscopy was conducted to investigate the optical properties. The direct band gap energy of the CdO thin film was 2.46 eV. The photovoltaic properties of the CdO/Si solarcell were examined under 100 mW/cm 2 solar radiation. The cell had an open circuit voltage (V oc ) of 460 mV, a short-circuit current density (J sc ) of
obtained so far are in the range of many reasons have been advanced for this low performance. Barrier height measurements in various Schottky barrier solar cells have shown that values are always in the range 0.7-0.9 eV regardless of the metal except for the case of gold and silver which form ohmic contacts with. This apparent plateau for the value of barrier heights is believed to be the principal cause of the low performance of the Schottky barrier solar cells. Studies on Schottky barrier solarcell indicate that there always exist copper rich regions at the interface between metal and regardless of the choice of the metal used. All Schottky type cells are therefore essentially solar cells and hence the constancy of the value of barrier height and the low electrical power conversion efficiency.
As it was said before, due to its low carrier density, a-Si layers behave like insulator layers, so fabricated structures exhibit a similar behavior to MIS capacitors. Therefore, their study was carried out by using the electrical characterization techniques developed for MIS structures. Electrical measurements were carried out putting the sample in a light-tight, electrically shielded box. In order to record electrical parameters at temperatures from liquid nitrogen temperature (≈77 K), samples were cooled in an Oxford DM1710 cryostat. An Oxford ITC 502 temperature controller was used to keep the temperature constant while the electrical measurements are carried out. Current-voltage (I-V) curves were mea- sured using the HP-4155B semiconductor parameter analyzer. Capacitance-voltage (C-V) and conductance- voltage (G-V) measurement setups involved a Keithley 4200SCS semiconductor analyzer. The experimental setup of the conductance transient technique consisted of an HP 3310A function generator to apply the bias pulses, an EG&G 5206 two-phase lock-in analyzer to measure the conductance, and an HP 54501A digital oscilloscope to record the complete conductance transients. Interface trap density (D it ) was measured by deep-level transient spec-