The objective of this research is to achieve high-efficiency, low-cost, commercial-ready, screen-printed Silicon (Si) solar cells by reducing material costs and raising cell efficiencies. Two specific solutions to material cost reduction are implemented in this thesis. The first one is low to medium concentrator (2-20 suns) Si solar cells. By using some optics to concentrate sunlight, the same amount of output power can be achieved with cell area reduced by a factor equal to the concentration ratio. Since the cost of optics is less than the semiconductor material, electricity price from the concentrator photovoltaics (PV) system is therefore reduced. The second solution is the use of epitaxially grown Si (epi-Si) wafers. This epi-Si technology bypasses three costly process steps (the need for polycrystalline silicon feedstock, ingot growth, and wafer slicing) compared to the traditional Si wafer technology and therefore reduces the material cost by up to 50% in a finished PV module. In addition, high efficiency Si solar cells with reduced metal contact recombination are studied and modeled by implementation of passivated contacts composed of tunnel oxide, n+ polycrystalline Si and metal on top of n-type Si absorber to reduce the cost ($/Wp) of PV module.

The buffer layer in Cu(In,Ga)Se2 solar cells can improve cell performance. In this work we make CdS buffer layer by chemical bath deposition (CBD) without ammonia. CBD without ammonia were sought out since ammonia is a volatile compound. Different recipes for making CdS were tested; only one of the tested recipes actually produced something that is worth further investigating. This recipe used sodium citrate, an innocuous compound instead of ammonia. The best performance was 0.15 % off from the reference.This is almost as good as the used baseline process. However the worst almost completely killed the solar cells. Cell performance dropped by more than absolute 10 %. This demonstrates that chemical bath deposition can have profound effects on the solar cell performance. When trying to improve the best cells only detrimental effects showed up. This might show that, a part in the recipe used, NaOH has detrimental effects on solar cells. Ammonia free chemical bath deposition is possible, however so far it has not produced as good results as the reference. The difference is however very small, which makes it worth further investigating with moreand better solar cell material.

The production of an efficient and low cost device has been the ultimate goal in the photovoltaic cell development. The fabrication and application of nanostructured materials in the field of energy conversion has been attracting a lot of attention. In this work, applications of surface plasmons (SPs) and photonic nanostructures to the field of energy conversion, specifically in the area of silicon solar cells and lanthanide energy upconversion (UC) luminescence applications were studied. Enhanced power conversion efficiency in bulk (single crystalline) silicon solar cells was demonstrated using an optimized mixture of the silver and gold nanoparticles (NPs) on the front of the cell to tackle the negative effect in the Au NPs plasmonic application. Then, a comparison of identically shaped metallic (Al, Au and Ag) and nonmetallic (SiO2) NPs integrated to the back contact of amorphous thin film silicon solar cells were investigated to solve a controversy issue in literature. The result indicates that parasitic absorption from metallic NPs might be a drawback to the SPs enhancement. A cost-effective fabrication of large area (5x5 cm2) honeycomb patterned transparent electrode for “folded” thin film solar cell application by combining the nanosphere lithography and electrodeposition were realized. Furthermore, the SPs enhanced tunable energy upconversion from NaYF4:Yb3+/Er3+ NPs in nanoslits were also demonstrated, our results shows that the relative red/green emission can be controlled by different plasmonic mode coupling. / Graduate / phwang@uvic.ca

This thesis studies p-i-n GaAs solar cells with self-assembled InAs quantum dots (QDs) inserted. The values of this work lie in three aspects. First, by comparing the cell performance with QDs in the i-region and the n-region, the photocurrent (PC) production from QDs by thermal activation and/or intermediate band (IB) absorption is proved to be much lower in efficiency than tunneling. Second, the efficiency of PC production from QDs, characterized by PC spectrum, is helpful to design QD-based photodetectors. Third, closely spaced InAs QD layers allow a strong inter-layer tunneling, leading to an effective PC production from QD deep states, potential for solar cell application. Fourth, from the temperature-dependent PC spectra the minority photohole thermal escape is found to be dominant on PC production from QDs in the n-region. The thermal activation energy reflects the potential variations formed by electron filling in QDs. Apart from InAs QDs, this thesis also explores the blinking correlation between two colloidal CdSe QDs. For QD distance of 1 µm or less, there is a bunched correlation at delay τ = 0, meaning that the two QDs blink synchronously. Such correlation disappears gradually as QD distance increases. The correlation is possibly caused by the stimulated emission between the two nearby QDs. / QC 20120507

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.

For the shortage of energy and the environmental issues, the development of solar cells has become an important technology. However, solar cells have low efficiency of energy conversion due to their high surface reflection on a flat Si substrate which is 38 %. To decrease the surface reflectance of the silicon solar cells, anti-reflection coatings (ARCs) are proposed on the solar cells. We use Lighttools software to investigate several kinds of ARCs to decrease the surface reflectance. We first consider the reflectance of the single-layer ARC with quarter wavelength. It can effectively decrease about 30 % surface reflection as compared with a flat Si substrate. The half-cylinder texture and the wave texture are designed on a PMMA single-layer coating. It is found that the half-cylinder ARC and the wave ARC can usefully diminish the surface reflectance for perpendicular light. Low reflectance can be achieved in the hemispherical microlens ARCs over an extended spectral region for omnidirectional incident light. The impact of the microlens sizes, periods, and arrangements are investigated. The lowest normal reflectance of the closely-packed triangular-lattice hemispherical microlens ARC is 4.8%. By adding smaller hemispherical microlenses, the surface reflectance of the hemispherical microlens ARC can be as low as 1.86 %. To obtain the lowest average surface reflectance, both-sided patterned surface texture ARCs are designed. Their lowest average surface reflectance is 2.24%. Finally, we simulate the reflectance of the nanowire ARCs. The influence of the wire length and the angle of inclination are discussed for high-efficiency and low-cost solar cells.

In this study, two kinds of homopolymers (PPDOT, and P3HT), and three different proportions of copolymers (PPDOT-co-P3HT=1:1, PPDOT-co-P3HT=3:1, and PPDOT-co-P3HT=1:3) have been synthesized successfully by Grignard metathesis. PDOT and 3HT, which are both of monomers, are electron-donating. Due to the fact that PDOT was caused larger than 3HT by pushing effect, it can change the conjugation length to be much longer, resulting in lower energy level of HOMO, and thus reduce energy gap of high molecular. These polymers possess optical bandgaps in the range of 1.908 to 1.922 eV. The desirable absorption attributes of these materials make them to be the excellent candidates for use in organic solar cells. In this study, the analysis and discussion of these polymers were measured by TGA, DSC, XRD, GPC, NMR, UV, PL, and AC-2 for thermal stability, crystallinity, structure and optical properties. From the XRD, materials of main chain ordered are well crystalline, which can increase the absorption of thiophene ring. By UV, we could find absorption region of infrared light increase that is beneficial to enhance ISC, but led to lower HOMO, and thus reduced VOC. However, the overall device power conversion efficiencies indicate that increasing ISC is much greater than decreasing VOC. Hence, power conversion efficiency increased. However, in PL, intensity of the emission is large, and it will cause components to quenching that lead to reduce its efficiency. We knew HOMO-LUMO energy level matching relations of polymer materials which were mixed with PCBM as the active layer of organic solar cells by UV-VIS and AC-2. From the instructions of device power conversion efficiency, because efficiency is not high, it causes the short circuit. The reason is (1) energy level can not match (2) the solubility of PPDOT is not very good, hence the film is not easy even. The way to improve is to identify a better solvent to increase its solubility.

In my study, I attempted to use the high electrical conductivity of graphite modified TiO2 nanoparticles to study the effect of graphite modification to the performance of dye-sensitized solar cell. Graphite oxide (GO) was successfully prepared by the improved Hummer¡¦s method. Graphenes that from the as-prepared GO reduced with hydrazine hydrate and sodium borohydride were characterized by Fourier transform infrared spectroscopy (FT-IR) and UV-visible spectroscopy. The performance of TiO2 based DSSC revealed a short-circuit photocurrent density of 11.24 mA/cm2, an open-circuit voltage of 0.66 V, and a fill factor of 0.48, yielding an overall conversion efficiency of 4.50%. The TiO2 / r-GO composite based DSSC showed higher efficiency than those standard DSSC, revealed a short-circuit photocurrent density of 18.48 mA/cm2, an open-circuit voltage of 0.68 V, and a fill factor of 0.51, yielding an overall conversion efficiency of 7.83%. On the other hand, we found the DSSC that treated with small amount of alcohol in making the TiO2 paste showed superior performance to that with untreated photoanode, the ratio of energy conversion efficiency being 7.11% to 4.50%.

Low-cost and high-efficiency are of continuous interest for the fabrication of solar cells. I-III-VI compound semiconductors Cu(In,Ga)Se2 (CIGS) are the most important absorber materials in developing thin film solar cells. The bandgap of CIGS varies from about 1.1 to 1.7 eV, which is within the maximum solar absorption region. This is very important for the optimum conversion efficiency. The extraordinarily high absorption coefficient from direct bandgap leads to thinner thickness and lower fabrication cost for its use in thin film solar cells. In this experiment, we deposit CuInGa alloy layer on Mo-coated soda-lime glass by RF sputtering and then use selenization process to form Cu(In,Ga)Se2. We study the characterization of sputtered CIG alloy layer and selenized CIGS thin film.

We use molecular beam deposition (MBD) system to grow CuAlSe2 thin film. The films have been characterized by electrical measurements but also by X-ray diffraction, electron probe microanalysis, optical measurements, scanning electron microscopy and photoluminescence. It is shown that CuAlSe2 thin film is chalcopyrite structure with a band gap of 2.65eV, p-type conductivity and the smallest resistivity is 1.26¡Ñ102(