Cheng, Ka Wing = 聚合物太陽能電池的研究 / 鄭家榮. / "December 2010." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 93-96). / Abstracts in English and Chinese. / Cheng, Ka Wing = Ju he wu tai yang neng dian chi de yan jiu / Zheng Jiarong. / Abstract --- p.i / 概要 --- p.iii / Acknowledgements --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- The Rise of Organic Photovoltaics --- p.1 / Chapter 1.2 --- General Review on Organic Photovoltaics --- p.3 / Chapter 1.2.1 --- Physics of Organic Photovoltaics --- p.4 / Chapter 1.2.2 --- Performance Analysis --- p.10 / Chapter 1.2.3 --- Calibration --- p.11 / Chapter 1.2.4 --- Device Architectures --- p.14 / Chapter 1.3 --- Morphology and Performance of Bulk Heterojunction Polymeric Solar Cells --- p.17 / Chapter 1.3.1 --- Choice of Solvent --- p.17 / Chapter 1.3.2 --- Effect of Annealing --- p.18 / Chapter 1.4 --- The Quest of Higher Efficiency --- p.18 / Chapter 1.5 --- Structure of This Thesis --- p.19 / Chapter 2 --- Optical Properties in a Multilayered Solar Cell --- p.21 / Chapter 2.1 --- Introduction --- p.21 / Chapter 2.2 --- Electromagnetic Waves in a Multilayered Thin Film --- p.22 / Chapter 2.3 --- Microcavity Effect --- p.33 / Chapter 2.4 --- Conclusion --- p.34 / Chapter 3 --- Improvement of Solar Cell Efficiency: Result of Simulation --- p.36 / Chapter 3.1 --- Introduction --- p.36 / Chapter 3.2 --- P3HT:PCBM Bulk Heterojunction Solar Cells --- p.36 / Chapter 3.2.1 --- Standard Devices --- p.37 / Chapter 3.2.2 --- Standard Devices with Inserted Silver Layer --- p.39 / Chapter 3.2.3 --- Silver Layer Inserted Devices Without PEDOT:PSS ... --- p.44 / Chapter 3.3 --- MEH-PPV:PCBM Bulk Heterojunction Solar Cells --- p.46 / Chapter 3.3.1 --- Standard Devices --- p.46 / Chapter 3.3.2 --- Standard Devices with Inserted Silver Layer --- p.50 / Chapter 3.3.3 --- Silver Layer Inserted Devices Without PEDOTiPSS . . --- p.52 / Chapter 3.4 --- Discussion --- p.54 / Chapter 3.5 --- Conclusion --- p.56 / Chapter 4 --- Experimental Results --- p.57 / Chapter 4.1 --- Introduction --- p.57 / Chapter 4.2 --- A General Study on Traditionally Structured Solar cell --- p.58 / Chapter 4.2.1 --- Standard Bulk Heterojunction Devices --- p.58 / Chapter 4.2.2 --- Effects of the Metal Electrodes --- p.59 / Chapter 4.2.3 --- Effects of Annealing Time --- p.60 / Chapter 4.3 --- Modified P3HT:PCBM Bulk Heterojunction Solar Cells --- p.61 / Chapter 4.3.1 --- Optimized Standard Devices --- p.61 / Chapter 4.3.2 --- Standard Devices with Inserted Silver Layer --- p.63 / Chapter 4.3.3 --- Silver Inserted Devices Without PEDOTiPSS --- p.64 / Chapter 4.4 --- Discussion --- p.68 / Chapter 4.5 --- Conclusion --- p.71 / Chapter 5 --- Conclusion --- p.73 / Chapter 5.1 --- Suggestion of Future Works --- p.75 / Chapter A --- Simulation Codes --- p.77 / Chapter A.1 --- P3HT:PCBM (1:1) Standard Device --- p.77 / Chapter B --- Instrumentation --- p.87 / Chapter C --- Sample Preparation --- p.90 / Bibliography --- p.93

Zheng, Shizhao = 聚合物太陽能電池的研究 / 鄭世昭. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references. / Abstracts in English and Chinese. / Zheng, Shizhao = Ju he wu tai yang neng dian chi de yan jiu / Zheng Shizhao. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgements --- p.iv / Publications --- p.v / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Overview of solar cells --- p.1 / Chapter 1.2 --- Organic solar cells --- p.5 / Chapter 1.3 --- Device structure and working principles --- p.8 / Chapter 1.4 --- Device fabrication and characterizations --- p.13 / Chapter 1.5 --- Summary of chapter 1 --- p.22 / Chapter Chapter 2 --- Instrumentations and Experimental Procedures / Chapter 2.1 --- Introduction --- p.27 / Chapter 2.2 --- Instrumentations --- p.27 / Chapter 2.3 --- Experimental procedures --- p.33 / Chapter 2.4 --- Summary of chapter 2 --- p.38 / Chapter Chapter 3 --- Study of polymer solar cells device based on P3HT:PCBM / Chapter 3.1 --- Introduction --- p.39 / Chapter 3.2 --- Effects of the choice of solvents and blending ratios --- p.42 / Chapter 3.3 --- Thermal annealing effect --- p.44 / Chapter 3.4 --- Effect of molecule weight and polydispersity --- p.48 / Chapter 3.5 --- Solvent soaking effect --- p.52 / Chapter 3.6 --- Summary of chapter 3 --- p.61 / Chapter Chapter 4 --- Study of polymer solar cell device based on new acceptor and new donor materials / Chapter 4.1 --- New acceptor material --- p.66 / Chapter 4.2 --- New donor materials --- p.73 / Chapter 4.3 --- Summary of chapter 4 --- p.81 / Chapter Chapter 5 --- Conclusions and future works / Chapter 5.1 --- Conclusions --- p.84 / Chapter 5.2 --- Future works --- p.86

The sun is a bountiful source of energy for our planet. .With the advent of photovoltaic cells, man has begun harnessing the sun's radiant energy, turning it into a form more directly useful: electricity. Commercially available solar cells currently operate at about 13% efficiency, sufficiently high to make them a viable source of electrical energy. It is of great interest, however, to improve their conversion efficiency, and to lower the cost of production so as to make them more economical, and thereby reduce our dependence upon traditional "dirty" sources of energy such as coal and oil. It has been found that an electrode coated with a thin film of nanocrystalline titanium dioxide, a very inexpensive and commonly available semiconductor, can be sensitized with a strong light-absorbing dye which can absorb the energy of sunlight and then transfer this energy as electronic charge into the electrode. A cell containing such an electrode is capable of producing a photocurrent at an appreciable voltage. The search is on to find the best sensitizing dye. It must absorb as much of the incident sunlight as possible, be capable of strong adsorption onto Ti02 so as to promote electron injection into the semiconductor, be relatively cheap and easy to synthesize, and be photochemically stable. It was the intent of this research to synthesize and test such a dye, a porphyrin dyad. The dyad was to be made from an electron donating moiety, meso-tetrakis(4-aminophenyl)porphyrin (TAPP), linked by an amide bond to an electron acceptor, meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP). This material eluded attempts at synthesis, due to the poor reactivity of the aminoporphyrin and to the difficulty in ensuring that only one amide bond formed. Characterization of the monomers was carried out, and conditions for their chromatographic separation were determined. Recommendations for successful synthesis of the dyad are given.

Many current technologies used in solar cell fabrication have been successfully adapted from the integrated circuits industry. The success of laser processing applications in this industry indicates that such techniques should be considered to reduce manufacturing costs and to improve electrical efficiency of solar cells. This thesis examines the application of advanced laser processing to improve the electrical performance and reduce manufacturing costs of solar cells. It focuses on several different aspects of laser processing; (1) understanding and characterising the effect of laser pulses on silicon, (2) developing new fabrication technologies and (3) integrating laser processes with working solar cell devices. The thesis begins with an overview of existing solar cell structures that incorporate laser processing. A study is then presented that explores the detrimental effects of laser processing, how it can be avoided and how to characterise its influence on solar cell electrical properties. Experimental results combine Yang defect etching, photoconductance decay measurements and a new technique of photoluminescence imaging to isolate the influence of laser ablation and laser melting on silicon wafers. This understanding is used in the development of several laser processes. A laser texturing technique is developed to texture the surface of multicrystalline wafers that cannot be effectively textured with the alkaline etches used on single crystal material. Three advanced laser contacting schemes; laser micro contacts, laser defined aluminium electrodes and laser doping, are assessed as techniques to improve cell efficiency and to reduce fabrication costs. In the final chapter the integration of laser processing with solar cell devices is demonstrated through the fabrication and characterisation of n-type double-sided solar cells with laser doped contacts. Efficiencies of up to 17.4% with an open circuit voltage of 672 mV are reported. This thesis also presents the application of a new characterisation technique, based on photoluminescence, to aid in improving both new and existing fabrication technologies. The work presented in this thesis demonstrates the applicability of advanced laser processing to solar cell fabrication and shows how laser processes can be used in a variety of ways to improve the electrical performance and reduce the fabrication complexity of solar cell devices.

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.

Photovoltaics is currently the fastest growing energy source in the world. Increasing the conversion efficiency towards the thermodynamic limits is the trend in research development. ???Third generation??? photovoltaics involves the investigation of ideas that may achieve this goal. Among the third generation concepts, the tandem cell structure has experimentally proven to have conversion efficiencies higher than a standard p-n junction solar cell. The alternative hot carrier solar cell design is one of the most elegant approaches. Energy selective contacts are crucial elements for the operation of hot carrier solar cells. Besides the carrier cooling problem within the absorber, carrier extraction has to be done through a narrow range of energy to minimise the interaction between the hot carriers in the absorber and the cooler carriers in the contacts. Resonant tunnelling through localised states, such as associated with atomic defects or with quantum dots in a dielectric matrix, may provide the required energy selectivity. A new model in studying the properties of resonant tunnelling through defects in an insulator is proposed and investigated. The resulting calculations are simple and useful in obtaining physical insight into the underlying tunneling processes. It is found that defects having a normal distribution along the tunnelling direction do not reduce the transmission coefficient dramatically, which increases the engineering prospects for fabrication. Silicon quantum dots embedded in an oxide provide the required deep energy confinement for room temperature resonant tunnelling operation. A single layer of silicon quantum dots in the centre of an oxide matrix are prepared by RF magnetron sputtering. The method has the advantage of controlling the dot size and the dot spatial position along the tunnelling direction. The presence of these crystalline silicon dots in the oxide is confirmed by high resolution transmission electron microscopy (HRTEM). A negative-differential resistance characteristic has been measured at room temperature on such structures fabricated on an N-type degenerated silicon wafer, a feature that can be explained by the desired resonant tunnelling process. A silicon quantum dot superlattice can be made by stacking multiple layers of silicon quantum dots. A model is proposed for calculating the band structure of such a silicon quantum dot superlattice, with the anisotropic silicon effective mass being taken into account. It suggests a high density of silicon quantum dots in a carbide matrix may provide the bandgap and required mobility for the top cell in the stacks for the recently proposed all-silicon tandem solar cell. The resonant tunnelling modeling and silicon quantum dot experiments developed have demonstrated new results relevant to energy selective contacts for hot carrier solar cells. Building on this work, the modeling study on silicon quantum dots may provide the theoretical basis for bandgap engineering of all-silicon tandem cells.

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.

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.

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