Polycrystalline silicon (pc-Si, grain size > 1??m, no amorphous tissue) on glass is an interesting material for thin-film solar cells due to the low costs, the abundance and the non-toxic character of Si, and the properties of pc-Si like long-term stability and lateral conductance. Glass as supporting material significantly complicates the fabrication process as it limits the thermal budget and the maximum temperature. In this work, the feasibility of forming large-grained pc-Si thin-film solar cells on glass by ion-assisted deposition (IAD) on aluminium-induced crystallisation (AIC) seed layers (ALICIA solar cells) is investigated. IAD allows epitaxial growth at high rate, and being based on evaporation, is of low cost (high source material usage, no toxic gases involved). High-quality epitaxy on (100)-oriented Si wafer substrates is demonstrated in a non{UHV environment, to further increase its industrial appli- cability. High{rate growth and a sacrificial protective layer control contamination problems associated with the non-UHV environment. The process is then trans- ferred to AIC-seeded glass and optimised, with particular focus on the influence of the glass. Using high-temperature rapid thermal annealing and hydrogenation as post-deposition treatments, ALICIA solar cells with a 1-Sun open-circuit voltage of 420 mV are achieved. Moreover, two novel characterisation techniques are presented. One allows the fast and non-destructive assessment of the structural quality of pc-Si films using opti- cal measurements. Furthermore, `impedance analysis', a novel capacitance-voltage measurement technique based on impedance spectroscopy, is presented. It allows the reliable determination of the absorber layer doping density and the built{in potential of non-ideal p-n junction solar cells. The latter is used to investigate the influence of post{deposition treatments on the n-type absorber layer doping of ALICIA solar cells. It is found, using temperature dependent impedance analysis, that unintentional doping and defects have a strong influence on the absorber layer doping. A maximum in the short-circuit current density of ALICIA solar cells is found for phosphorus concentrations in the absorber of 1??1017 cm??3. For such ALI- CIA cells a base difusion length in the range 600 - 950nm, a short{circuit current density in the range 10 - 13.5 mA/cm2 and an energy conversion efficiency of 2.2% are obtained.

This thesis work demonstrates the feasibility to fabricate high-efficiency crystalline silicon solar cells by using metal stencil printing technique to replace screen printing or electroless plating techniques for implementing crystalline silicon solar cell front metallization. The developed laser-cut stainless steel stencils successfully challenge two of the cell performance limitations associated with commercial screen printing technology: the wide and non-uniform front gridline fingers and low height-to-width aspect ratio of the fingers. These limitations lower the short circuit current density, the fill factor and, in turn, the efficiency of a screen printed solar cell. Metal stencils are capable of printing fine, high and continuous features on the cell front that have a high aspect ratio. Both single-level and double-level structured stainless steel stencils for solar cell front metallization have been developed, with laser-cut double-level stainless steel stencils being demonstrated for the first time worldwide. Both of them are able to print fine, high and continuous gridline pattern to the front surfaces of solar cells in one step, with a certain number of special short bridges being put at the places where fingers meet busbar and along fingers and busbar. The deformation issue of the very thin stainless steel foils due to its thermal expansion in the process of laser cutting is solved by increasing the energy content in each laser pulse that impinges upon the stainless steel foil with changed Q-switch frequencies, while maintaining the laser average output energy in unit time to an optimum value. A chemical etching process has been developed to etch the dross that results from laser cutting, resulting in well formed metal stencils suitable for printing. By a comparison between the metal stencil printed and conventional mesh screen printed silicon solar cells, which are fabricated on similar Cz silicon wafers with a almost identical cell processing sequence except for using different front contact printing masks, the following conclusions are reached: Fired Ag finger lines with 75-??m width on finished solar cells, using a doublelevel stainless steel stencil can be achieved. In contrast, the fired Ag finger line on finished solar cells using a traditional mesh screen is 121-??m wide. The stencil printed finger is smoother and more uniform than by screen printing and the former has a 25-??m fired finger height with a 0.33 height-to-width aspect ratio, compared to a 10-??m fired finger height with a 0.08 height-to-width aspect ratio for the later. With these advantages, the 4-cm2 stencil-printed silicon solar cells has an averaged 1.28 mA/cm2 higher short circuit current and an averaged 5.9% higher efficiency than the 4-cm2 screen printed silicon solar cell, which identifies one of the key advantages of solar cell metallization schemes by using metal stencil printing in place of screen printing. Using a ???feedback alignment??? method for registration of the laser-formed metal stencil printed pattern and the laser-formed groove pattern, Ag paste can be printed and filled into wafer grooves by using a hand-operated without an optical vision system. The fired finger profile is 50-??m wide and 22-??m high. The best metal stencil printed, selective emitter silicon solar cell demonstrates a 34.2 mA/cm2 short circuit current density, 625 mV open circuit voltage, 0.77 fill factor and 16.4% efficiency, with an excellent spectral response at short wavelengths due to its selective emitter cell structure. It is believed that the performance of this type of solar cell can be enhanced with a screen printer that has an optical vision system and an automatic alignment device. The successful development of metal stencil printed silicon solar cells demonstrates the feasibility of the metal stencil printing as a beneficial technology for the PV industry.

Polycrystalline silicon (pc-Si, grain size > 1??m, no amorphous tissue) on glass is an interesting material for thin-film solar cells due to the low costs, the abundance and the non-toxic character of Si, and the properties of pc-Si like long-term stability and lateral conductance. Glass as supporting material significantly complicates the fabrication process as it limits the thermal budget and the maximum temperature. In this work, the feasibility of forming large-grained pc-Si thin-film solar cells on glass by ion-assisted deposition (IAD) on aluminium-induced crystallisation (AIC) seed layers (ALICIA solar cells) is investigated. IAD allows epitaxial growth at high rate, and being based on evaporation, is of low cost (high source material usage, no toxic gases involved). High-quality epitaxy on (100)-oriented Si wafer substrates is demonstrated in a non{UHV environment, to further increase its industrial appli- cability. High{rate growth and a sacrificial protective layer control contamination problems associated with the non-UHV environment. The process is then trans- ferred to AIC-seeded glass and optimised, with particular focus on the influence of the glass. Using high-temperature rapid thermal annealing and hydrogenation as post-deposition treatments, ALICIA solar cells with a 1-Sun open-circuit voltage of 420 mV are achieved. Moreover, two novel characterisation techniques are presented. One allows the fast and non-destructive assessment of the structural quality of pc-Si films using opti- cal measurements. Furthermore, `impedance analysis', a novel capacitance-voltage measurement technique based on impedance spectroscopy, is presented. It allows the reliable determination of the absorber layer doping density and the built{in potential of non-ideal p-n junction solar cells. The latter is used to investigate the influence of post{deposition treatments on the n-type absorber layer doping of ALICIA solar cells. It is found, using temperature dependent impedance analysis, that unintentional doping and defects have a strong influence on the absorber layer doping. A maximum in the short-circuit current density of ALICIA solar cells is found for phosphorus concentrations in the absorber of 1??1017 cm??3. For such ALI- CIA cells a base difusion length in the range 600 - 950nm, a short{circuit current density in the range 10 - 13.5 mA/cm2 and an energy conversion efficiency of 2.2% are obtained.

Polycrystalline silicon (pc-Si, grain size > 1??m, no amorphous tissue) on glass is an interesting material for thin-film solar cells due to the low costs, the abundance and the non-toxic character of Si, and the properties of pc-Si like long-term stability and lateral conductance. Glass as supporting material significantly complicates the fabrication process as it limits the thermal budget and the maximum temperature. In this work, the feasibility of forming large-grained pc-Si thin-film solar cells on glass by ion-assisted deposition (IAD) on aluminium-induced crystallisation (AIC) seed layers (ALICIA solar cells) is investigated. IAD allows epitaxial growth at high rate, and being based on evaporation, is of low cost (high source material usage, no toxic gases involved). High-quality epitaxy on (100)-oriented Si wafer substrates is demonstrated in a non{UHV environment, to further increase its industrial appli- cability. High{rate growth and a sacrificial protective layer control contamination problems associated with the non-UHV environment. The process is then trans- ferred to AIC-seeded glass and optimised, with particular focus on the influence of the glass. Using high-temperature rapid thermal annealing and hydrogenation as post-deposition treatments, ALICIA solar cells with a 1-Sun open-circuit voltage of 420 mV are achieved. Moreover, two novel characterisation techniques are presented. One allows the fast and non-destructive assessment of the structural quality of pc-Si films using opti- cal measurements. Furthermore, `impedance analysis', a novel capacitance-voltage measurement technique based on impedance spectroscopy, is presented. It allows the reliable determination of the absorber layer doping density and the built{in potential of non-ideal p-n junction solar cells. The latter is used to investigate the influence of post{deposition treatments on the n-type absorber layer doping of ALICIA solar cells. It is found, using temperature dependent impedance analysis, that unintentional doping and defects have a strong influence on the absorber layer doping. A maximum in the short-circuit current density of ALICIA solar cells is found for phosphorus concentrations in the absorber of 1??1017 cm??3. For such ALI- CIA cells a base difusion length in the range 600 - 950nm, a short{circuit current density in the range 10 - 13.5 mA/cm2 and an energy conversion efficiency of 2.2% are obtained.

Polycrystalline silicon (poly-Si) thin-film solar cells are receiving attention by many researchers in recent times. The focus of this thesis is the evaporated ALICE solar cell, a thin-film poly-Si solar cell fabricated on a glass superstrate by e-beam evaporation. The acronymn ALICE comes from - ALuminium Induced Crystallization Solid Phase Epitaxy. The concept is first to form a high-quality crystalline silicon layer on glass by Aluminium Induced Crystallization (AIC). The AIC seed layer (grain size>20 ??m) acts as the template from which the crystalline information is transferred into the silicon over-layer by solid-phase epitaxy (SPE). As a result, the ALICE solar cells have much larger grain size compared to the poly-Si thin-film solar cell (2~3 ??m) by random nucleation and growth (RNG). This leads to the minimized grain boundary recombination and hence potential improved conversion efficiency. The temperature of 200??C is found to be optimal for the deposition of amorphous Si (a-Si) precursor thin films. The epitaxy process of the ALICE cell is successful, proving the feasibility and reliability of the deposition and post-treatment processes. The ALICE cell is successfully metallized using a bifacial interdigitated scheme. Wet etching using KOH is introduced to realize the uniform Si etching, and phosphoric acid etching is introduced to remove the local shunts in the ALICE cell. The results show that the material quality of ALICE solar cells are much worse than that of the AIC seed layer, which is related to the poor epitaxy quality on (111) planes grown from the AIC seed layer. Additional experiments show that the fraction of (100) oriented grains in AIC is the main factor in determining the material quality and the resulting solar cell performance, rather than grain size. Therefore, both a high fraction of (100) oriented grains and large grain size are required for AIC seed layers to achieve the ALICE solar cells with superior performance. Comparison of the ALICE cells prepared at different base pressures and deposition rates show that the base pressure is much less important than the deposition rate. Therefore, the capital cost of the evaporator system can be reduced and hence potentially the manufacturing cost of solar cells. The densification anneal was introduced to improve the crystal quality of poly-Si thin films by SPE. It is shown that the cause is the structural relaxation induced into the a-Si film, instead of the prevention of the oxygen percolation. The crystal quality of c-Si films obtained from low-rate (50 nm/min) evaporated a-Si is considerably improved by densification anneal, whereas densification has no beneficial effect on c-Si films obtained from high-rate (300 nm/min) evaporated a-Si. However, the densification anneal has no improvement on the electrical performance of ALICE solar cell. The ALICE solar cell performances are strongly related to the doping level in the absorber layer. The optimal doping density needs to be determined to achieve the best performance. The highest Voc and Jsc are simultaneously achieved when the minimum phosphorous doping density of ~5.5??1015 cm-3 (unintentionally doped) is applied for the evaporated ALICE solar cells. Since silicon is a weak absorber and ALICE solar cell has only ~1.5 ??m thickness, light trapping is applied to enhance the light absorption of the visible and the red light. Three different approaches are applied: ALICE cells on textured glass sheet, back surface reflector and thicker Si film. The ALICE cells on textured glass suffer from a significant loss of performance. The only successful approach to improve the light trapping in this thesis is to apply white paint as back surface reflector, which increases the Jsc drastically (~60%) compared to a planar sample. Analysis of the optical properties of poly-Si thin films is important as it assists the design of the thin-film solar cells. It is found that there is enhanced absorption in the visible wavelengths. This is mainly attributed to defected a-Si material at the grain boundaries. The hydrogenation process does not affect this enhanced absorption. The optical analysis proves that large grain size is desired to obtain high performance poly-Si thin-film solar cell, e.g. ALICE solar cell. At the end of this research, ALICE cells with η~3.83%, Voc~485 mV, Jsc~17.75 mA/cm2 have been achieved.

Thesis (Ph. D.)--Virginia Polytechnic Institute, 1964. / Vita. Abstract. Includes bibliographical references (leaves 43-44). Also available via the Internet.

Thesis (Ph. D.)--George Mason University, 2007. / Title from PDF t.p. (viewed Jan. 21, 2008). Thesis director: Mulpuri V. Rao. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering. Vita: p. 128. Includes bibliographical references (p. 122-127). Also available in print.

Thesis ( Ph.D.) -- McMaster University, 1997. / Computer disk in pocket. Includes bibliographical references. Also available via World Wide Web.

Thesis (M.S.) in Physics--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 82-87).

Thesis (M.S.) in Mechanical Engineering--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 121-124).