With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.

With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis deals with three phase inverters and the different control strategies that can be associated with an inverter being used together. The first part of this thesis discusses the present research in the fields of PV panels, motor drive systems and three phase inverters along with their control. This control includes various strategies like MPPT, Volts-Hertz and modulation index compensation. Incorporating these techniques together is the goal of this thesis. A new topology for operating an open end motor drive system has also been discusses, where a boost converter and a flyback converter have been used in cascade to run a three phase motor. The main advantage of this is increasing the number of levels and improving the quality of the output voltage, not to mention a few other benefits of having the proposed circuit. A new algorithm has also been designed for starting and stopping the motor, which controls the current drawn from the power source during starting.

A research report submitted in partial fulfilment to the degree of Master of Science in the School of Physics, University of the Witwatersrand, 2018 / With the global energy consumption at an all-time high and the demand for energy estimated to triple by 2050, renewable energy sources such as solar are pivotal in an addressing this global energy demand. Solar power generation by photovoltaic cells enjoys several advantages compared to other forms of electricity generation such as a reduced fossil fuel dependence, modularity, easy and flexible installation, and scalability. The development of novel solar cells that offer increased efficiencies is an integral component of the process of addressing the global energy needs. Solar cell device simulations offer a cost-effective means to explore the impact of different material properties on the overall efficiency of the solar cell. The use of ab initio calculated material properties that serve as an import for the device simulations offers a means to easily study and estimate the typical solar cell efficiencies of different types of solar cells. The implementation of new light harnessing features, like frequency conversion layers or plasmonic nanoparticles, and the integration of these futures into existing device simulation codes serves as a useful tool that aids solar cell development. This work explores the theoretical and numerical background for the simulation of solar cell devices. A brief explanation of how ab initio calculated parameters can be used, together with the implementation of frequency conversion techniques in existing simulation codes is given. It is shown that the solar cell performance parameters can be well approximated using ab intio parameters. Also, the positive effect of frequency conversion techniques is demonstrated with examples of how this tool can be implemented in existing solar cell device simulation codes. The approaches discussed in this work can serve as a good framework for the modeling of novel solar cell devices / MT 2019

No description available.

PV Inverters have the task of tracking the maximum power point (MPP), and regulating the solar energy generation to this optimal operation point. The second task is the conversion of direct current produced by the solar modules into alternating current compatible with the grid. A new inverter approach such as a single phase micro inverter is emerging aimed to overcome some of the challenges of centralized inverters. As a counterpart to the central inverter, a micro inverter is a small compact module attached directly to each solar panel. To provide for the constantly increasing demand for a small size, light weight and high efficiency micro inverter, soft switching power conversion technologies have been employed. The switching stress can be minimized by turning on/off each switch when the voltage across it or the current through it is zero at the switching transition. With the addition of auxiliary circuits such as auxiliary switches and LC resonant components the so called soft switching condition can be achieved for semiconductor devices. Four main purposes to investigate the soft switching technologies for singlephase micro-inverter are: (1) to improve overall efficiency by creating the favorable operating conditions for power devices using soft-switching techniques; iv (2) to shrink the reactive components by pushing the switching frequency to a higher range with decent efficiency. (3) to ensure soft switching does not exacerbate inverter performance, meaning all conventional PWM algorithms can be applied in order to meet IEEE standards. (4) to investigate which soft switching techniques offer the cheapest topology and control strategy as cost and simple control are crucial for low power inverter applications. An overview on the existing soft-switching inverter topologies for single phase inverter technology is summarized. A new quasi resonant DC link that allows for pulse- width- modulation (PWM) is presented in this thesis. The proposed quasi resonant DC link provides zero-voltage switching (ZVS) condition for the main devices by resonating the DC-link voltage to zero via three auxiliary switches and LC components. The operating principle and mode analysis are given. The simulation was carried out to verify the proposed soft switching technique. A 150W 120VAC single-phase prototype was built. The experimental results show that the soft switching for four main switches can be realized under different load conditions and the peak efficiency can reach 95.6%. The proposed quasi DC link can be applied to both single-phase and three-phase DC/AC micro inverter. In order to boost efficiency and increase power density it is important to evaluate the power loss mechanism in each stage of operation of the micro inverter. Using the datasheet parameters of the commercially available semiconductor switches, conduction and switching losses were estimated. This thesis presents a method to analyze power losses of the new resonant DC link inverter which alleviates topology v optimization and MOSFET selection. An analytical, yet simple model for calculating the conduction and switching losses was developed. With this model a rough calculation of efficiency can be done, which helps to speed up the design process and to increase efficiency.

This dissertation introduces a new planning and operational tool to integrate photovoltaic (PV) systems into the utility's generation mix. It is recognized that much of the existing research concentrated on the central PV system, its operations, and long-term planning with PV system and concluded that technical problems in PV_ operation. will _power was subtracted from the utility load with the expectation that conventional generation would meet the load. This approach is valid for small penetration levels and for PV facilities connected near the load centers. Second, PV system was studied on a case-by-case basis. This made the interactions between the PV systems and conventional power systems not well known to the operator in the dispatch center on one hand, and to the PV system manufacturer, on the other hand. In addition, several constraints such as thermal generation ramping capabilities, energy costs, tie-line interchange, spinning reserve requirements, hydro availability and generating capacity, and pumped-storage scheduling are not adequately represented in this process. These are real problems and their solutions are sought in this dissertation. Finally, the value of PV systems does not lie only in serving load, but also in reducing problems associated with emissions. It is felt that a comprehensive methodology that would take into account the PV system characteristics and the forth mentioned constraints, as well as more global penetration is developed. The proposed methodology is designed to handle load dynamics and PV fluctuations, so as to minimize operational problems. The objective of this study is to determine the economic and operational impacts when large photovoltaic systems are incorporated into the electric utility generation mix. The proposed methodology handles combustion turbines, hydro and pumped-storage hydro power systems. Performance analysis shows that hydro availability, generation mix and characteristics, PV power output dynamics and performance, time of the year, and energy costs influence the economic and operational impacts of large-scale PV generation. Results show that while hydro dispatching increases acceptable PV penetration levels, generation mix and energy costs influence the breakeven capital cost. According to this study, for a 10 percent PV penetration level (1200 MW) and high energy costs, the breakeven capital cost is $968/kW and $1200/kW for Richmond (Virginia) and Raleigh (North Carolina), respectively. This corresponds to an energy cost of 3.20 and 3.00 ¢/kWh for Richmond and Raleigh. / Ph. D.

In this thesis, the structural, optical and electrical properties of crystalline silicon quantum dots (SiQDs) are examined for application to silicon based tandem cells. The approach has been to concentrate on all silicon devices by taking advantage of quantum confinement in low-dimensional Si. RF magnetron co-sputtering provided the capability of creating superlattice structures in conjunction with high temperature annealing, to form Si nanocrystals in an oxide matrix. Structural techniques, including Fourier transform infrared spectroscopy (FTIR), micro-Raman spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Secondary ion mass spectroscopy (SIM) were employed to gather structural information about the SiQD/SiO2 SLs. The result combine presents that the packing density of Si QDs, correlated to the oxygen content of the silicon rich oxide layer can be control independently. The effect of Si nanocrystallite density on Raman scattering is investigated. The preliminary results present that a decrease in the oxygen content (x) results in an increased sharpness of the Strokes-mode peak of nanocrystalline Si, attributed to an increase in the proportion of crystalline Si because of the increased number of SiQDs. However the influence of the surface region on the crystallite core intensity scattering becomes dominant, when SiQD size diameter is very small (less than 3 nm). The present work shows that a decrease in x-content leading to an increase of the SiQD concentration, initially results in the enhancement of the lateral conductivity in the SiQD superlattice material. In this work, the Al contacting scheme, using a prolonged heat treatment technique at elevated temperature less than the eutectic point of Al and Si (577C) has been successfully applied to making Ohmic contacts on both SiQD SLs in oxide and nitride matrices. Activation energy (Ea) of SiQDs, extracted from a linear Arrhenius plot is investigated in the present work in order to expand the understanding of engineering electrical injection in laterally active paths. It is found that a lower barrier height of dielectric matrix influences to the lateral electron transport of the SiQDs in such dielectric matrix. PL results confirm that the band gap of surface oxidized SiQDs widens due to quantum confinement. The present results reveal that the strong peak (Q-peak) due to quantum confinement is more effective in the emission with increasing SiQD concentration. The surface oxide is believed to play an important role in the reduction of SiQD luminescence due to a trapped exiciton. It is concluded that SiQDs surface oxide accompanied by a SiO2 matrix may not provide a good passivation in very small SiQD size. However the energy band gap and conductivity of the SiQDs are tunablity, in the optimum range of SiQD size and concentration. This observation may be important for future nanoelectronics applications.

In this thesis, the structural, optical and electrical properties of crystalline silicon quantum dots (SiQDs) are examined for application to silicon based tandem cells. The approach has been to concentrate on all silicon devices by taking advantage of quantum confinement in low-dimensional Si. RF magnetron co-sputtering provided the capability of creating superlattice structures in conjunction with high temperature annealing, to form Si nanocrystals in an oxide matrix. Structural techniques, including Fourier transform infrared spectroscopy (FTIR), micro-Raman spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Secondary ion mass spectroscopy (SIM) were employed to gather structural information about the SiQD/SiO2 SLs. The result combine presents that the packing density of Si QDs, correlated to the oxygen content of the silicon rich oxide layer can be control independently. The effect of Si nanocrystallite density on Raman scattering is investigated. The preliminary results present that a decrease in the oxygen content (x) results in an increased sharpness of the Strokes-mode peak of nanocrystalline Si, attributed to an increase in the proportion of crystalline Si because of the increased number of SiQDs. However the influence of the surface region on the crystallite core intensity scattering becomes dominant, when SiQD size diameter is very small (less than 3 nm). The present work shows that a decrease in x-content leading to an increase of the SiQD concentration, initially results in the enhancement of the lateral conductivity in the SiQD superlattice material. In this work, the Al contacting scheme, using a prolonged heat treatment technique at elevated temperature less than the eutectic point of Al and Si (577C) has been successfully applied to making Ohmic contacts on both SiQD SLs in oxide and nitride matrices. Activation energy (Ea) of SiQDs, extracted from a linear Arrhenius plot is investigated in the present work in order to expand the understanding of engineering electrical injection in laterally active paths. It is found that a lower barrier height of dielectric matrix influences to the lateral electron transport of the SiQDs in such dielectric matrix. PL results confirm that the band gap of surface oxidized SiQDs widens due to quantum confinement. The present results reveal that the strong peak (Q-peak) due to quantum confinement is more effective in the emission with increasing SiQD concentration. The surface oxide is believed to play an important role in the reduction of SiQD luminescence due to a trapped exiciton. It is concluded that SiQDs surface oxide accompanied by a SiO2 matrix may not provide a good passivation in very small SiQD size. However the energy band gap and conductivity of the SiQDs are tunablity, in the optimum range of SiQD size and concentration. This observation may be important for future nanoelectronics applications.

CAPES / A preocupação em alcançar o desenvolvimento sustentável está cada vez mais presente na construção civil, sendo este o setor que mais contribui com os maiores níveis de emissões de gases de efeito estufa, devido ao grande consumo de energia e recursos naturais. Adicionalmente, os edifícios despendem de uma grande quantidade energética para aplicações cotidianas e em muitos países, as fontes são provenientes de fontes não-renováveis, causando dependência de combustíveis fósseis e consequentemente elevação nos índices de emissões de CO2. Portanto, as “transições de sustentabilidade” mediante a aplicação de novos sistemas de energia renováveis, os quais apresentam emissões reduzidas, como por exemplo, a energia solar fotovoltaica, viabilizam essa mudança. Essa fonte de energia está cada vez mais presente na matriz energética mundial, seja pela aplicação de usinas fotovoltaicas de grande porte ou por meio de usinas geradoras de mini e microgeração incorporada às edificações, atuando como geração distribuída inserida no meio urbano. Neste sentido, este trabalho tem por objetivo contribuir com redução da demanda, com a eficiência energética e a quantificação das emissões de CO2 equivalente que podem ser evitadas com a energia gerada, por meio da utilização da energia fotovoltaica na UTFPR – câmpus Curitiba. A metodologia consiste na análise dos parâmetros de irradiação local horizontal e inclinada coletados por meio do portal do INMET, do Atlas Brasileiro de Energia Solar e do Piranômetro da UTFPR para aplicação do software Radiasol. Por sua vez, efetuouse o estudo do perfil de cargas da instituição, a fim de identificar os momentos de maiores consumo e demanda por energia elétrica, através da seleção de dias típicos elencados no decorrer do ano. A análise das coberturas possibilitou o levantamento de áreas disponíveis e análise de sombreamento, e através dos dados gerados pelos Sistemas Fotovoltaicos Conectados à Rede existentes foram elaborados cenários, objetivando a contribuição energética do câmpus. Por fim, foram calculados os níveis de penetração energéticos, bem como o fator efetivo de capacidade de carga, quantificando o aumento da capacidade disponível da rede elétrica atribuída à geração fotovoltaica e as respectivas emissões evitadas. Os resultados obtidos mostram que a UTFPR - câmpus Curitiba apresenta um vasto potencial para a geração de energia fotovoltaica, sendo que a instituição poderia alocar um sistema com potência instalada total de 3,25 MW, e gerar um total anual de energia de 4,37 GWh. Com relação ao nível de penetração energético total calculado, obteve-se 489,97%, o que significa a ocorrência de injeção do excedente de energia fotogerada no sistema elétrico. Pode-se concluir que além da possibilidade de redução de custos com energia elétrica, existiria uma redução significativa nas emissões de GEE’s referentes ao cálculo de CO2 podendo evitar a emissão de 284,43 tCO2 ao ano. / The concern of achieving sustainable development is increasingly present in civil construction, which is the sector that shows the highest levels of greenhouse gas emissions due to its high consumption of energy and natural resources. Buildings use a large amount of energy in their day-to-day use, and in many countries this energy comes from non-renewable sources, causing dependence on fossil fuels and consequently increasing CO2 emissions."Sustainable transitions" make change possible through the application of new renewable energy systems, which present reduced emissions, e.g. solar photovoltaic energy. This energy source is increasingly present in the global energy matrix, both in large-scale photovoltaic plants and smalland micro-generation incorporated into buildings, acting as distributed generation in urban environments. The objective of this thesis is to contribute to a reduction in demand, with energy efficiency and to the quantification of equivalent CO2 emissions that could be avoided with energy generated through the use of photovoltaic energy at UTFPR’s Curitiba campus. The methodology consists of the analysis of horizontal and inclined local irradiation parameters collected through the INMET portal, the Brazilian Solar Energy Atlas and the piranometer at UTFPR, and in the application of the software Radiasol. The study of the load profile of the institution was carried out in order to identify periods of greater consumption and demand for electric energy, through the selection of typical days during the year. The analysis of the coverages allowed the survey of available areas and a shading analysis. Through the data generated by the existing grid-connected photovoltaic system, scenarios were elaborated to model the energy contribution of the three campus. Finally, the energy penetration levels and the effectiveness factor of the load capacity were calculated quantifying the increase of the available capacity of the electricity grid, attributed to the photovoltaic generation, as well as the respective emissions avoided. The results show that the Curitiba campus of UTFPR have a vast potential for the generation of photovoltaic energy, and the institution could allocate a system with a total installed power of 3.25 MW, generating an annual total of 4.37 GWh of energy. The calculated total energy penetration level of 489.97% was obtained, which implies the injection of a surplus of photo-generated energy into the electric system. It can be concluded that besides the possibility of reducing electricity costs, there would be a significant reduction in GHG emissions calculated at 284.43 tCO2 per year.