A two-dimensional finite-element model was developed to simulate the optoelectronic performance of thin-film, p-i-n junction solar cells. One or three p-i-n junctions filled the region between the front window and back reflector; semiconductor layers were made from mixtures of two different alloys of hydrogenated amorphous silicon; empirical relationships between the complex-valued relative optical permittivity and the bandgap were used; a transparent-conducting-oxide layer was attached to the front surface of the solar cell; and a metallic reflector, either flat or periodically corrugated, was attached to the back surface. First, frequency-domain Maxwell postulates were solved to determine the spatial absorption of photons and thus the generation of electron–hole pairs. The AM1.5G solar spectrum was taken to represent the incident solar flux. Second, drift-diffusion equations were solved for the steady-state electron and hole densities. Numerical results indicate that increasing the number of p-i-n junctions from one to three may increase the solar-cell efficiency by up to 14%. In the case of single p-i-n junction solar cells, our simulations indicate that efficiency may be increased by up to 17% by incorporating a periodically corrugated back reflector (as opposed to a flat back reflector) and by tailoring the bandgap profile in the i layer.
KEYWORDS: Solar cells, Reflectors, Photons, Thin film solar cells, Semiconductors, Doping, Optical simulations, Finite element methods, Absorption, Solids
A two-dimensional finite-element model was developed to simulate both the optical and electrical characteristics of thin-film, p-i-n junction, solar cells. For a preliminary assessment of the model’s capabilities, one or more p-i-n junctions were allowed to fill the region between the front and back surfaces; the semiconductor layers were taken to be made from mixtures of three different alloys of hydrogenated amorphous silicon; empirical relationships between the complex-valued relative optical permittivity and the bandgap were used; a transparent-conducting oxide layer was taken to be attached to the front surface of the solar cell; and a metallic reflector, which may be periodically corrugated, was supposed to be attached to the back surface. First the frequency-domain Maxwell postulates were solved in order to determine the absorption of solar photons and the subsequent generation of electron-hole pairs, with the AM1.5G solar spectrum taken to represent the incident solar flux. Next, the drift-diffusion equations were solved to track the evolution of electron and hole densities to a steady state. Preliminary numerical results from our model indicate that by increasing the number of p-i-n junctions from one to three, the solar-cell efficiency may be increased. The efficiency may be further increased by incorporating a periodically-corrugated back reflector, as opposed to a flat back reflector, in the case of a single p-i-n junction solar cell. We plan to apply the two-dimensional finite-element model for more complicated solar cells.
KEYWORDS: Solar energy, Solar cells, Manufacturing, Photovoltaics, Silicon, Wind energy, Systems modeling, Electronics, System integration, Data conversion
According to United Nation, world population may reach 10.1 billion by the year 2100. The fossil fuel based global economy is not sustainable. For sustainable global green energy scenario we must consider free fuel based energy conversion, environmental concerns and conservation of water. Photovoltaics (PV) offers a unique opportunity to solve the 21st century’s electricity generation because solar energy is essentially unlimited and PV systems provide electricity without any undesirable impact on the environment. Innovative paths for green energy conversion and storage are proposed in areas of R and D, manufacturing and system integration, energy policy and financing. With existing silicon PV system manufacturing, the implementation of new innovative energy policies and new innovative business model can provide immediately large capacity of electricity generation to developed, emerging and underdeveloped economies.
Integrated photonics has the potential of fabricating a diverse set of photonic systems on a single substrate. At
nanoscales (< 100 nm), the properties of material depend on quantum confinements. The challenge is to integrate these
unique properties of nanostructures into low-cost manufacturing. For material deposition, a photo-assisted monolayer
deposition technique can provide nanomaterials with an ultra-low defect density. Epitaxial dielectrics offer the
possibility of growing defect-free optical materials including compound semiconductors on silicon substrates. In this
paper, we have also provided manufacturing directions that must be incorporated for developing the next generation of
integrated photonics.
Rising demands of energy in emerging economies, coupled with the green house gas emissions related problems around the globe have provided a unique opportunity of exploiting the advantages offered by photovoltaic (PV) systems for green energy electricity generation. Similar to cell phones, power generated by PV systems can reach over two billion people worldwide who have no access to clean energy. Only silicon based PV devices meet the low-cost manufacturing criterion of clean energy conversion (abundance of raw material and no environmental health and safety issues). The use of larger size glass substrates and manufacturing techniques similar to the ones used by the liquid crystal display industry and the large scale manufacturing of amorphous silicon thin films based modules (~ GW per year manufacturing at a single location) can lead to installed PV system cost of $3/Wp. This will open a huge market for grid connected PV systems and related markets. With further research and development, this approach can provide $2/Wp installed PV system costs in the next few years. At this cost level, PV electricity generation is competitive with any other technology, and PV power generation can be a dominant electricity generation technology in the 21st century.
In this paper, we have shown that superconducting electronics can provide a complementary role to microelectronics and optoelectronics. High temperature superconductors can be used in the fabrication of ultra fast three terminal devices as well as for chip-to-chip interconnections. If the next generations of DRAMs require cooling at 77 K, high temperature superconductors offer several advantages over metals as the interconnect material. A new photoeffect reported in this paper can give rise to new devices and can be used to couple microwave and optoelectronic technology. Major challenge is to develop a low temperature processing technology that is compatible to semiconductor industry. Experimental results are presented indicating the potential of rapid isothermal processing assisted metalorganic chemical vapor deposition (MOCVD) method as a technique suitable for manufacturing.
Rapid isothermal processing (RIP) based on incoherent sources of light is emerging as a reduced thermal budget (product of processing time and temperature) processing technique. As compared to a stand-alone annealing unit, the integration of RIP with other processing units leading to integrated RIP systems is very attractive for the next generation of devices and circuits. From cost and performance point of view, the integrated rapid isothermal processing of these devices offers several advantages compared to their ex-situ rapid isothermal annealed and furnace annealed counterparts. The authors have used an integrated RIP system for the in- situ rapid isothermal surface cleaning of InP and GaAs substrates and in-situ metallization of InP and GaAs Schottky diodes. As compared to ex-situ annealing, in-situ rapid isothermal cleaning of InP and GaAs surfaces prior to metallization followed by in-situ annealing results in improved electrical characteristics. In addition to the well established short time processing feature of RIP, the dominance of radiation spectrum from vacuum ultraviolet (VUV) region to visible region can provide lower temperature processing compared to furnace processing.
Rapid isothermal processing (RIP) based on incoherent sources of light is emerging as a reduced thermal budget (product of processing time and temperature) processing technique. As compared to a stand alone annealing unit the integration of RIP with other processing units leading to integrated RIP systems is very attractive for the next generation of devices and circuits. From cost and performance point of view the integrated rapid isothermal processing of these devices offers several advantages compared to their exsitu rapid isothermal annealed and furnace annealed counterparts. We have used an integrated RIP system for the insitu rapid isothermal surface cleaning of InP and GaAs substrates and insitu metallization of InP and GaAs Schottky diodes. As compared to exsitu annealing insitu rapid isothermal cleaning of InP and GaAs surfaces prior to metallization followed by insitu annealing results in improved electrical characteristics. We have also integrated a plasma source with a RIP system and studied the thermal oxidation of Si at 300C followed by an insitu rapid isothermal anneal. In this paper we also show that photo effects play a significant part in RIP. I.
Metal organic chemical vapor deposition (MOCVD) has the potential of emerging as
a viable technique to fabricate ribbons, tapes, coated wires, and the deposition of films of
high temperature superconductors, and related materials. As a reduced thermal budget
processing technique, rapid isothermal processing (RIP) based on incoherent radiation as
the source of energy can be usefully coupled to conventional MOCVD. In this paper we
report on the deposition and characterization of high quality superconducting thin films
of Y-Ba-Cu-O (YBCO) on MgO, SrTiO3, and YSZ substrates by RIP assisted MOCVD.
Some preliminary results are also presented for the deposition of BaF2, Y203 and MgO
on silicon substrates. It is envisaged that high energy photons from the incoherent light
source and the use of a mixture of N2O and 02 as the oxygen source, assist chemical
reactions and lower the overall thermal budget for processing of YBCO films.
This paper discusses established electronics technology with prospects for incorporation
of high critical temperature (Ta) superconductors, the projected results of introducing
superconductors into conventional semiconductor electronics, and processing issues in the
construction of hybrid devices.
Rapid isothermal processing and microwave-excited gases (N2O + O2 + He) have been used to deposit YBCO films on YSZ substrates. The thermal cycle represents the lowest thermal budget used by any other researcher. A Tc of 75 K was observed. These results coupled with the capability of depositing YBCO on BaF2/Si substrate indicate the usefulness of MOCVD for the practical realization of superconductor/semiconductor hybrid devices.
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