MBE ( Molecular Beam Epitaxy ) technique can obtain high quality of GaSb/GaAs hetero-junction structure and control epilayers precisely.It has 7¢Mlattice mismatch between GaAs ( substrate ) and GaSb ( thin film ), but if we control beam flux ratio (V/III) and substrate temperature exactly, we can obtain high quality of epilayer. The growth mechanisms related to the major factors of (1) Beam flux ratio (V/III)¡B(2) Substrate temperature. The properties of GaSb epilayers are characterized by different methods such as the X-ray diffraction. The optimum growth conditions 500¢J of substrate temperature and the V/III flux ratio about 2.5 have been obtained. On the basis of this condition, We use simulation program for solar cell ( Scaps ), to simulate GaSb/GaAs hetero-junction solar cell structure, to try the possibility of the GaSb/GaAs hetero-junction structure in solar cells. From the simulation result, we know if the doped concentration in the two semiconductor materials and thickness are suitability, and if we can control the concentration of interface states under a suitable value, the efficiency of the solar cell can well. On the basis of this result, the same for thermo-photovoltaic (TPV), its' efficiency will also well.

In this research, CuInSe2 thin film is grown at 350¢J low temperature by photo-assisted co-evaporation system to fabricate PI (polyimide) substrate flexible thin film solar cells. The low temperature growing CuInSe2 is analyzed by raman spectroscopy. Besides, sputtering Mo thin film on PI and CIS/Mo/PI contact properties are also researched for device fabrication. By studying the Ar pressure and Mo internal stress relationship during the deposition, the Mo layer has been fabricated with both low resistivity and good adhesion. The sheet resistance of Mo layer is 1.95 £[/¡¼ and shows ohmic contact with CuInSe2 at temperature below 350¢J. Raman spectroscopy shows that photo-assisted CuInSe2 has stronger and thinner A1 peak than which without light. Two-stage growing can help eliminating Cu2Se and background signals further. CA structure vibration modes are involved in the asymmetric A1 peak broadening. The SLG/Mo/CIS/CdS/ZnO:Al/Al structured device has open voltage, Voc = 0.320 V, short cut current, Isc = 3.61 mA, and solar cell fill factor, FF = 49.8 %. On the other hand, PI/Mo/CIS/CdS/ZnO:Al/Al structured device has open voltage, Voc = 0.318 V, short cut current, Isc = 2.71 mA, and solar cell fill factor, FF = 39.0 %¡C

Semiconductors absorb photos with energy greater than their band gap energy may induce electron-hole pairs. In semiconductor physics, increasing charge carrier improves the electric conductivity of semiconductor. The following methodology was taken to investigate the electric conductivity and the electron hole pairs affected performance of a dye sensitized solar cell. I applied 3 specific monochromatic light (365nm, 405nm and 437nm, respectively.) mixed with xenon light and normal xenon light separately illuminating on dye sensitized solar cells. At the assumption of the normalized photon to current conversion efficiency of solar cell illuminated by 437nm monochromatic light is 100%, the normalized photon to current conversion efficiency of the solar cell illuminated by 365nm monochromatic light was only 28%, however, that illuminated by 365nm monochromatic light mixed xenon light raised to 58%. The more intense mixed light produced more excited electrons than only 365nm monochromatic light. The holes generated by 365nm monochromatic light is easier to be captured by the electrons in the more intense mixed xenon light irradiation results in higher photon to current conversion efficiency. The output of photocurrent of the dye sensitized solar cell irradiated by 365nm ultraviolet light mixed xenon light was enhanced most significantly by 6.53% compared with that by normal xenon light irradiation.

In my research, I use sucrose to modify TiO2 nanoparticles to study the influence of sucrose modification in the performance of dye-sensitized solar cell. Two types of TiO2 are used in the experiments, one is P-25 (80% anatase, Degussa, Germany) and the other is ST-21 (100% anatase, Ishihara Sangyo, Japan). The results shows that the solar cells with TiO2 photoanode sintered in N2 has better conversion efficiency than that sintered in air. On the other hand, the TiO2 with 0.08 g/mL sucrose modification and sintered in N2 has the best conversion efficiency than the others with different sucrose concentration modifications and the highest conversion efficiency reaches 5.55 %. The performance of P-25 with 0.08 g/mL sucrose made solar cell is 10.9% higher than that without sucrose modification TiO2 photoanode made solar cell and the performance of ST-21 with 0.08 g/mL sucrose made solar cell is 5.4% higher than that without sucrose modification.

In this work, an electronic gas company was chosen as a research objective to understand how to execute the strategic planning and competition in an emerging market such as solar cell industry. First, individual industrial analysis was carried out for both electronic gas industry and solar cell industry, which provide the connections and characteristics between these two industrial segments. A project was selected as an example for detail explanation. It covers the initial competition attitudes of individual competitors; the crisis of silane shortage during the new industry segment emerging; how our company deals with the shortage crisis; how to identify the penetration strategies through a series of sales tactics and to confine the competitor advantages in order to obtain the maximum profit. In the conclusions, the track of competition planning was reviewed and the characteristics of gas industry were categorized for future research interests. Meanwhile, related theories were used to compared and contrasted in order to support the business case from the academic approach. At the end, a summary of competition review was included to outline how the organization rigidity causing an near-miss crisis to the overall strategic planning; why the early engagements to the emerging industrial segment is extremely critical to the electronic gas company; how the front line sales and marketing personnel to identify the business opportunities; also how to obtain the necessary resources in an internal competition.

The objective of the research in this thesis was to develop high-efficiency n-type silicon solar cells at low-cost to reach grid parity. This was accomplished by reducing the electrical and optical losses in solar cells through understanding of fundamental physics and loss mechanisms, development of process technologies, cell design, and modeling. All these technology enhancements provided a 3.44% absolute increase in efficiency over the 17.4% efficient n-type PERT solar cell. Finally, 20.84% efficient n-type PERT (passivated emitter and rear totally diffused) solar cells were achieved on commercial grade 239cm2 n-type Cz silicon wafers with optimized front boron emitter without boron-rich layer and phosphorus back surface field, silicon dioxide/silicon nitride stack for surface passivation, optimized front grid pattern with screen printed 5 busbars and 100 gridlines, and improved rear contact with laser opening and physical vapor deposition aluminum. This thesis also suggested research directions to improve cell efficiency further and attain ≥21% efficient n-type solar cells which involves three additional technology developments including the use of floating busbars, selective emitters, and negatively charged aluminum oxide (Al2O3) film for boron emitter surface passivation.

The commercially available solar cells suffer from low efficiency and high cost. This would avoid presence of solar cells as a secure energy resource in the market. Problems stem from two facts. Firstly, band gap of materials deployed for cell fabrication do not match the solar spectrum. Secondly, harvesting all the generated electrons is imperfect due to presence of many non-radiative recombination processes and, thermalization of electrons. To transcend these deficiencies, third generation of solar has been introduced. This new generation renders a whole new concept both in design and materials of solar cells scope. One of new introduction to solar cell field is Quantum Dot (QD). QD offers a broad range of tunability. The optical and electrical properties of QDs can be altered by choice of material, size and shape; therefore; they have great potential for high efficiency cell fabrication. QDs are mainly grown via MBE or synthesized via Colloidal solutions. QDs could be integrated as a part of one of new and promising third generation cells, named Intermediate Band Solar Cells. QDs could be employed as the intermediate level. If MBE is the selected method for cell fabrication, QDs would grow in a matrix of barrier material accompanied with a wetting layer. Wetting layer would disturb the ideal condition predicted in theory for gaining the high efficiency. To study how wetting layer would affect IB performance two sets of simulations have been carried out. One part is done with COSMOL. In this part different number of QDs layers have been simulated with and without wetting layer. The result showed that parasitic effect of wetting layer could not be eliminated large stacks of QD are stacked together, to achieve the promised efficient wetting layer should be eliminated from the system. In MATLAB part QDs have been approximated with simple cuboid. The main aim in this part was to compare how the result of taking into the account the real shape differs from a simple approach which has been the most reported the most in literature. If all the restrains on achieving high efficiency of IBSC are met, still one major draw- back remains and, that is high cost of MBE process. This would hinder mass production of IB cell. One possible potential method to gradually replace MBE can be Colloidal QDs. Colloidal QDs are fairly low cost and easy to fabricate. In this work, colloidal crystal growth was examined. The best condition for monolayer deposition was obtained and, the feasibility of crystal growth was demonstrated. additionally, There was an attempt to grow more than one layer and investigate result of embedding QDs in a barrier of another material.

The electricity generation using photovoltaic (PV) solar cells is the most viable and promising alternative to the fossil-fuel based technologies which are threatening world&rsquo / s climate. PV cells directly convert solar energy into electrical power through an absorption process that takes place in a solid state device which is commonly fabricated using semiconductors. These devices can be employed for many years with almost no degradation and maintenance. PV technologies have been diversified in different directions in recent years. Many technologies with different advantages have been developed. However, with more than %85 percent market share, Si wafer based solar cells have been the most widely used solar cell type. This is partly due to the fact that Si technology is well known from the microelectronic industry. This thesis is concerned with the production of single crystalline silicon solar cells and optimization of process parameters through the characterization of each processing step. Process steps of solar cell fabrications, namely, the light trapping by texturing, cleaning, solid state diffusion, lithography, annealing, anti reflective coating, edge isolation have all been studied with a systematic approach. Each sample set has been characterized by measuring I-V characteristics, quantum efficiencies and reflectance characteristics. The best efficiency that we reached during this study is 10.37% under AM1.5G illumination. This is below the efficiency values of the commercially available solar cells. The most apparent reason for the low efficiency value is the series resistance caused by the thin metal contacts. It is observed that the efficiency upon the reduction of series resistance effect is reduced. We have shown that the texturing and anti-reflective coating have a critically important effect for light management for better efficiency values. Finally we have investigated the fabrication of metal nanoparticles on the Si wafer for possible utilization of plasmonic oscillation in them for light trapping. The self assembly formation of gold nanoparticles on silicon surface has been successfully demonstrated. The optical properties of the nanoparticles have been studied / however, further and more detailed analysis is required.

abstract: To date, the most popular and dominant material for commercial solar cells is crystalline silicon (or wafer-Si). It has the highest cell efficiency and cell lifetime out of all commercial solar cells. Although the potential of crystalline-Si solar cells in supplying energy demands is enormous, their future growth will likely be constrained by two major bottlenecks. The first is the high electricity input to produce crystalline-Si solar cells and modules, and the second is the limited supply of silver (Ag) reserves. These bottlenecks prevent crystalline-Si solar cells from reaching terawatt-scale deployment, which means the electricity produced by crystalline-Si solar cells would never fulfill a noticeable portion of our energy demands in the future. In order to solve the issue of Ag limitation for the front metal grid, aluminum (Al) electroplating has been developed as an alternative metallization technique in the fabrication of crystalline-Si solar cells. The plating is carried out in a near-room-temperature ionic liquid by means of galvanostatic electrolysis. It has been found that dense, adherent Al deposits with resistivity in the high 10^–6 ohm-cm range can be reproducibly obtained directly on Si substrates and nickel seed layers. An all-Al Si solar cell, with an electroplated Al front electrode and a screen-printed Al back electrode, has been successfully demonstrated based on commercial p-type monocrystalline-Si solar cells, and its efficiency is approaching 15%. Further optimization of the cell fabrication process, in particular a suitable patterning technique for the front silicon nitride layer, is expected to increase the efficiency of the cell to ~18%. This shows the potential of Al electroplating in cell metallization is promising and replacing Ag with Al as the front finger electrode is feasible. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016

Our reliance on semiconductors is on the rise with the ever growing use of electronics in our daily life. Organic-inorganic hybrid lead halide perovskites have emerged as a prime alternative to current standard and expensive semiconductors because of its use of abundant elements and the ease of solution processing. This thesis has shed light on the ink-to-solid conversion during the one-step solution process of hybrid perovskite formulations from DMF. We utilize a suite of in situ diagnostic probes including high speed optical microscopy, optical reflectance and absorbance, and grazing incidence wide angle x-ray scattering (GIWAXS), all performed during spin coating, to monitor the solution thinning behavior, changes in optical absorbance, and nucleation and growth of crystalline phases of the precursor and perovskite. The starting formulation experiences solvent-solute interactions within seconds of casting, leading to the formation of a wet gel with nanoscale features visible by in situ GIWAXS. The wet gel subsequently gives way to the formation of ordered precursor solvates (equimolar iodide and chloride solutions) or disordered precursor solvates (equimolar bromide or 3:1 chloride), depending upon the halide and MAI content. The ordered precursor solute phases are stable and retain the solvent for long durations, resulting in consistent conversion behavior to the perovskite phase and solar-cell performance. In this thesis, we develop a firm understanding of the solvent engineering process in which an anti-solvent is used during the coating process through the solvent mixture of GBL and DMSO in different ratios. It has been shown that solvent engineering produce pin hole-free films, justifying its wide adoption across the field. We then translate our learnings from the lab scale spin coating process to the industrial friendly blade coating process. Here we compare the ink solidification and film formation mechanisms of CH3NH3PbI3 in solutions we used to understand the key scientific insights through spin coating. We observe high-quality film formation for T > 100oC, namely in conditions which inhibit the formation of the crystalline intermediate complex phases. In doing so, we achieve fast and direct formation of the perovskite phase with solar cells yielding PCE > 17%.