Material requirements for the adoption of unconventional silicon crystal and wafer growth techniques for high-efficiency solar cells

Silicon wafers comprise approximately 40% of crystalline silicon module cost, and represent an area of great technological innovation potential. Paradoxically, unconventional wafer-growth techniques have thus far failed to displace multicrystalline and Czochralski silicon, despite four decades of innovation. One of the shortcomings of most unconventional materials has been a persistent carrier lifetime deficit in comparison to established wafer technologies, which limits the device efficiency potential. In this perspective article, we review a defect-management framework that has proven successful in enabling millisecond lifetimes in kerfless and cast materials. Control of dislocations and slowly diffusing metal point defects during growth, coupled to effective control of fast-diffusing species during cell processing, is critical to enable high cell efficiencies. To accelerate the pace of novel wafer development, we discuss approaches to rapidly evaluate the device efficiency potential of unconventional wafers from injection-dependent lifetime measurements

The integration of knowledge management in the operations of Malaysian banks

The globalization of financial markets forced bankers to be knowledge-based and be more efficient in managing knowledge in their banking operations. The importance of this function is accentuated further by the call from the Central Bank of Malaysia (Bank Negara Malaysia) to integrate the concepts of knowledge management in banking operations. In this paper, we discuss a research model called: Banking Knowledge Management Model (BKMM),which encompasses knowledge creation, knowledge retention and knowledge sharing and more importantly, how each of these elements can be integrated to enhance the quality of banking operations. The various components of BKMM are explained and we illustrate the application of BKMM in two Malaysian commercial banks. We find that the two banks apply the concept of knowledge management in line with BKMM but differ in their knowledge management approach. Despite different approach, both banks derive many benefits from applying knowledge management in their operations. We expect a wider application of BKMM by other banks in Malaysia would create a culture that promote and enhance knowledge management in the banking sector

ADVANCED STUDIES ON TRANSFER IMPEDANCE WITH APPLICATION TO AFTER-TREATMENT DEVICES AND MICRO-PERFORATED PANEL ABSORBERS

This work is primarily comprised of five self-contained papers. Three papers are applications oriented. A common element in the first three papers is that micro-perforated panels (MPP), the permeable membranes in diesel particulate filters, and a source impedance are all modeled as a transfer impedance. The first paper deals with enhancing the performance of micro-perforated panels by partitioning the backing cavity. Several different backing schemes are considered which enhance the performance without increasing the total volume of the MPP and backing. In the second paper, a finite element modeling approach is used to model diesel particulate filters below and above the plane wave cutoff frequency. The filter itself is modeled using a symmetric finite element model and results are compared to plane wave theory. After the transfer matrix of the filters is known, it is used in three-dimensional finite and boundary element models. The third paper is a tutorial that shows how a source impedance can be modeled using transfer impedance approaches in finite element analysis. The approach used is useful for better understanding the resonance effects caused by pipes upstream and downstream of the exhaust. The fourth paper examines the best practice for the two-load transmission loss measurement. This method was integral to obtaining the measurements for validating the diesel particulate filter models. The fifth paper proposes transmission and insertion loss metrics for multi-inlet mufflers. It is shown that the transmission loss depends on the amplitude and phase relationship between sources (at the inlets) whereas insertion loss depends on both the source strength and impedance for each inlet

Reliability Enhancement of Perovskite Solar Cells: Role of Low-Dimensional Materials for Interfacial Modifications

239 p.Perovskite solar cells (PSCs) have drawn a great deal of attention in the photovoltaic community owing to their excellent power conversion efficiency and low-cost production. Interfaces remain the weakest part of the complete device, holding their further improvement towards commercialization. This thesis focuses on a comprehensive understanding of the photo-induced charge transfer dynamics and the reliability enhancement of PSCs based on interfacial modification through low-dimensional semiconductor materials. It is found that the two-dimensional (2D) transition metal dichalcogenides (TMDs)-based interfacial layer minimizes the energy barrier and charge accumulation at the interface of the perovskite/charge-transport-layer while prompting extraction of photo-induced charges in the device. The reduction of interface recombination and the enhancement of charge transfer dynamics at the NiOx nanocrystal/perovskite interface were further constructed by the application of a molecularly engineered dithieno thiophene-based thin organic semiconductor layer on NiOx. The developed strategy is further extended with the implementation of a 2D-C3N4 polymeric network, which enables greater PCE byreducing non-radiative losses and faulty charge build-up at the NiOx/perovskite interface. The greater stability of perovskite is established owing to the strong coordination of MA+ cations with unbound nitrogen electron pairs in the C3N4. A thorough grasp of the perovskite/electron transport layer interface was further studied, and it is found that 2D-TiS2 had a greater effect on PV performance when paired with PC60BM under ideal addition. The results presented in this thesis offer unique insight into the interfacial modification using low-dimensional materials to achieve simultaneous high efficiency and stability in PSCs.BCMaterials: Basque Center for Materials Applications & Nanostructure

MPPT battery charge controller with lorawan communication interface

Mestrado de dupla diplomação com Tunisia Private University (ULT Tunisie)Renewable sources, such as Photovoltaic Systems (PV), have been employed for decades to focus on cleaner types of electricity generation. Today, it is a subject of worry as to how to cut costs and enhance efficiency in order to harness and utilise these natural resources in the best way possible. As a result, the concept of Maximum Power Point Tracking Technique (MPPT) evolved, which is essentially a system used by charge controllers for wind turbines and Photovoltaic Systems to use and also give a maximised power output. This thesis is primarily focused with the application of such a system in order to achieve controlled photovoltaic power using the MPPT mechanism. The main goal is to add LoRaWAN capability such as to be able to transmit information regarding the solar charge battery controller internal state A micro-controller, which is part of a larger circuit, such as a solar charge controller, is required for MPPT hardware implementation. The heart of the hardware circuit is the solar charge controller. Furthermore, the system was integrated with a dashboard to provide easier access to data for analysis from anywhere, eliminating the physical work of data collecting.Fontes de energia renovável, como é o caso dos sistemas fotovoltaicos, têm sido vindo a ser cada vez mais utilizadas como alternativas menos impactantes do ponto de vista ambiental. Atualmente, é motivo de preocupação o recurso a métodos e tecnologias que permitam aproveitar os recursos naturais sustentáveis e, ao mesmo tempo, reduzir os custos e aumentar a sua eficiência. Neste contexto, é importante o recurso a técnicas de seguimento de ponto de potência máximo (MPPT), usado por controladores de carga para turbinas eólicas e sistemas fotovoltaicos, de modo a extrair a máxima potência do sistema elétrico de produção de energia. Esta tese assenta no desenvolvimento de um sistema fotovoltaico capaz de regular o processo de carga para baterias de gel, dotada de mecanismo MPPT integrado e com a capacidade de transmitir toda a telemetria associada à operação do regulador usando o protocolo LoRaWAN. Este sistema de controlo de carga é baseado num microcontrolador que implementa o algoritmo MQTT e os dados enviados, via LoRaWAN, são apresentados numa interface gráfica

Opto-Electro-Thermal Approach to Modeling Photovoltaic Performance and Reliability from Cell to Module

Thanks to technology advancement in recent decades, the levelized cost of electricity (LCOE) of solar photovoltaics (PV) has finally been driven down close to that of traditional fossil fuels. Still, PV only provides approximately 0.5% of the total electricity consumption in the United States. To make PV more competitive with other energy resources, we must continuously reduce the LCOE of PV through improving their performance and reliability. As PV efficiencies approach the theoretical limit, however, further improvements are difficult. Meanwhile, solar modules in the field regularly fail prematurely before the manufacturers 25-year warranty. Therefore, future PV research needs innovative approaches and inventive solutions to continuously drive LCOE down. In this work, we present a novel approach to PV system design and analysis. The approach, comprised of three components: multiscale, multiphysics, and time, aims at systemically and collaboratively improving the performance and reliability of PV. First, we establish a simulation framework for translating the cell-level characteristics to the module level (multiscale). This framework has been demonstrated to reduce the cell-to-module efficiency gap. The framework also enables the investigation of module-level reliability. Physics-based compact models -the building blocks for this multiscale framework are, however, still missing or underdeveloped for promising materials such as perovskites and CIGS. Hence, we have developed compact models for these two technologies, which analytically describe salient features of their operation as a function of illumination and temperature. The models are also suitable for integration into a large-scale circuit network to simulate a solar module. In the second aspect of the approach, we study the fundamental physics underlying the notorious self-heating effects for PV and examine their detrimental influence on the electrical performance (multiphysics). After ascertaining the sources of self-heating, we propose novel optics-based self-cooling methodologies to reduce the operating temperature. The cooling technique developed in this work has been predicted to substantially enhance the efficiency and durability of commercial Si solar modules. In the third and last aspect of the approach, we have established a simulation framework that can forward predict the future energy yield for PV systems for financial scrutiny and inversely mine the historical field data to diagnose the pathology of degraded solar modules (time). The framework, which physically accounts for environmental factors (e.g., irradiance, temperature), can generate accurate projection and insightful analysis of the geographic-and technology-specific performance and reliability of solar modules. For the forward modeling, we simulate the optimization and predict the performance of bifacial solar modules to rigorously evaluate this emerging technology in a global context. For the inverse modeling, we apply this framework to physically mine the 20-year field data for a nearly worn-out silicon PV system and successfully pin down the primary degradation pathways, something that is beyond the capability of conventional methods. This framework can be applied to solar farms installed globally (an abundant yet unexploited testbed) to establish a rich database of these geographic-and technology-dependent degradation processes, a knowledge prerequisite for the next-generation reliability-aware design of PV systems. Finally, we note that the research paradigm for PV developed in this work can also be applied to other applications, e.g., battery and electronics, which share similar technical challenges for performance and reliability

Layer-by-Layer Construction Strategies Towards Efficient CZTS Solar Cells

Solar energy has very high potential for ensuring the world’s energy requirements for the long-term future. Earth-abundant materials like Cu2ZnSnS4 (CZTS) are especially desirable, with a non-toxic, low-cost nature, though the quaternary nature allows for a lot of crystal structure variability, and thus underwhelming performance. This Ph.D. thesis is devoted to deepening the understanding of the CZTS material formation, and the processes that can be used to control it, to construct a low-cost, high efficiency CZTS-based solar cell. The layer-by-layer approach presented within this thesis shows great potential for rectifying the problem. CZTS nanocrystal (NC) stoichiometric control was achieved, and led to reproducible structure formation within the films (Chapter 2). Structural correlations to photoresponse for these films were established by means of synchrotron spectroscopies, and increased charge-carrier flux out of the NC film (Chapter 3). Refinement of the NC stoichiometry (Chapter 4) enhanced these results, and extended the structural correlations. CdS addition to the CZTS film to form the p-n junction was investigated, and confirmed water intercalations in the film arising during CdS deposition. Mild thermal treatments were found to purify the films, and lead to further amplification of the charge-carrier flux (Chapter 5). The CZTS/CdS films were found to not have the desired enhancement to the overall photoresponse due to surface oxides, and poor alignment in the valence/conduction bands of the materials interface. It was discovered that acetic acid etching of the CZTS layer prior to CdS addition removed the oxides, and drastically improved the charge-carrier flux (Chapter 6). In fact, the band structure was aligned favorably to create an ideal p-n junction. The band structure diagram was well established, and the electron flow in the conduction band overlap was confirmed to be favored. The full device was built by combining all refinement processes, and adding ZnO and Al-doped ZnO window layers with atomic layer deposition (Chapter 7). A high open-circuit potential of 0.85 V, and competitive device efficiency of 8.5% were achieved. The layer-by-layer approach is thus proven throughout this thesis to be a highly effective strategy and anticipated to guide intelligent solar cell designs and fabrications

A Kinetic Monte Carlo Study of Mesoscopic Perovskite Solar Cell Performance Behavior

Perovskite solar cells have received considerable attention in recent years due to their low processing cost and high energy conversion efficiency. However, the mechanisms of perovskite solar cell performance are not fully understood. Models based on probabilistic and statistical approaches can be used to simulate, optimize, and predict perovskite solar cell photovoltaic performance, and they can also guide experimental processing and fabrication conditions to achieve higher photovoltaic efficiency. This work developed a 3D model based on the kinetic Monte Carlo (KMC) approach to simulate 3D morphology of perovskite-based solar cells and predict their photovoltaic performance. The model incorporated the physical behavior of perovskite cells with respect to their charge generation, transport, and recombination characteristics. KMC simulation results showed that perovskite films with the pin holes-free and a homogenous perovskite capping layer of 400 nm thickness produced a maximum photovoltaic efficiency of 20.85%, resulting in minimal charge transport time (τt) and maximum charge carrier recombination lifetime (τr). Photovoltaic performance from the fabricated device has been used to validate this simulation model. This model provides significant conceptual advances in identifying current performance constraints and guiding novel device designs that enhance overall perovskite photovoltaic performance