This research is to synthesize polyaniline (PANI) thin film for polymer solar cells as a hole transport layer by using potentiostatic deposition of electrochemical method. In our previous studies, we have shown that the power conversion efficiencies of the solar cell device were improved for the slow polymerization rate. We choose the potentiostatic deposition method to improve the polymerization rate of PANI for the application in industry. In this study, we investigated optical transmittance, absorption spectrum, Highest Occupied Molecular Orbital (HOMO), surface roughness, and surface morphology of the PANI thin film by changing voltages and to discuss the factors on device efficiency. Then, we compared the device structures with hole transport layer PEDOT: PSS by spin-coating process. We found PANI thin films synthesized from different voltages, and the transmittance measurement results were similar. In addition, we found HOMO, surface roughness, and surface morphology of PANI thin film that varies with different voltages. The power conversion efficiencies of the device mainly were affected by the surface roughness and morphology of PANI thin film surface. Comparing to other parameters, PANI thin film polymerized at 0.8V owns the most appropriate surface roughness and surface morphology. The power conversion efficiency was up to 1.52% under AM 1.5G illumination based on ITO (150 nm) / PANI (75 nm) / P3HT: PCBM (100 nm) / Al (200 nm), and the device area of 0.16 cm2.

Data centres lie at the heart of almost every service on the Internet. Data centres are used to provide search results, to power social media, to store and index email, to host “cloud” applications, for online retail and to provide a myriad of other web services. Consequently the more efficient they can be made the better for all of us. The power of modern data centres is in combining commodity off-the-shelf server hardware and network equipment to provide what Google’s Barrosso and Ho ̈lzle describe as “warehouse scale” computers. Data centres rely on TCP, a transport protocol that was originally designed for use in the Internet. Like other such protocols, TCP has been optimised to maximise throughput, usually by filling up queues at the bottleneck. However, for most applications within a data centre network latency is more critical than throughput. Consequently the choice of transport protocol becomes a bottleneck for performance. My thesis is that the solution to this is to move away from the use of one-size-fits-all transport protocols towards ones that have been designed to reduce latency across the data centre and which can dynamically respond to the needs of the applications. This dissertation focuses on optimising the transport layer in data centre networks. In particular I address the question of whether any single transport mechanism can be flexible enough to cater to the needs of all data centre traffic. I show that one leading protocol (DCTCP) has been heavily optimised for certain network conditions. I then explore approaches that seek to minimise latency for applications that care about it while still allowing throughput-intensive applications to receive a good level of service. My key contributions to this are Silo and Trevi. Trevi is a novel transport system for storage traffic that utilises fountain coding to max- imise throughput and minimise latency while being agnostic to drop, thus allowing storage traffic to be pushed out of the way when latency sensitive traffic is present in the network. Silo is an admission control system that is designed to give tenants of a multi-tenant data centre guaranteed low latency network performance. Both of these were developed in collaboration with others.

>Magister Scientiae - MSc / TiO2 nanoparticle films are important electron transport layers (ETLs) in photovoltaics such as dye-sensitised, perovskite and polymer hetero-junction solar cells. These films, however, have significant electron trap-sites as a result of the large density of oxygen vacancies present in nanosized TiO2. These trap-sites cause electron-hole recombination and ultimately lower photon-tocurrent conversion efficiency of the underlying cell during operation. Doping the TiO2 lattice with low atomic number elements such as nitrogen is a proven method to overcoming the charge transport inefficiency of TiO2 ETLs; another is the use of one-dimensional (1D) nanowires (NWs), instead of nanoparticles. Modification of TiO2 with non-metals leads to optical bandgap narrowing, improvement in electron conductivity and increased electron lifetime in the ETL layer. However, a lot of scope exists in understanding and fully quantifying the relationship between optical property, for example light transmission and bandgap modification, versus the doping concentration and type. Most doping approaches are in-situ and involve the addition of a dopant precursor (usually a salt) during the synthesis of TiO2 nanostructures – this invariably leads to uncontrolled doping levels, anion contamination and poor-quality materials – a need thus exists to develop simple, controllable doping approaches. One such approach, which forms the basis of this study, is ex-situ doping by means of plasma generated species in a controlled environment. This field of study is fairly novel and not widely studied, requiring more research to understand the doping mechanisms and influence on the optical and electronic properties of the underlying nanomaterials. In particular, controlled doping of TiO2 with nitrogen using radio-frequency generated (RF) plasma requires vigorous experimentation and characterisation. Inaccuracy of the deposition parameters during exposure remains a common drawback for this approach in addition to a lack of understanding of the surface interaction between the N2 species and specimen during irradiation.

>Magister Scientiae - MSc / TiO2 nanoparticle films are important electron transport layers (ETLs) in photovoltaics such as dye-sensitised, perovskite and polymer hetero-junction solar cells. These films, however, have significant electron trap-sites as a result of the large density of oxygen vacancies present in nano-sized TiO2. These trap-sites cause electron-hole recombination and ultimately lower photon-to-current conversion efficiency of the underlying cell during operation. Doping the TiO2 lattice with low atomic number elements such as nitrogen is a proven method to overcoming the charge transport inefficiency of TiO2 ETLs; another is the use of one-dimensional (1D) nanowires (NWs), instead of nanoparticles.

>Magister Scientiae - MSc / Perovskite solar cells have attracted a tremendous amount of research interest in the scientific community recently, owing to their remarkable performance reaching up to 22% power conversion efficiency (PCE) in merely 6 to 7 years of development. Numerous advantages such as reduced price of raw materials, ease of fabrication and so on, have contributed to their increased popularity.

The world is becoming strongly dependent on computers, and on distributed communication between computers. As a result of this, communication security is important, sometimes critically so, to many day-to-day activities. Finding strategies for discovering attacks against security protocols and for proving security protocols correct is an important area of research. An increasingly popular technique that is used to simplify the design of security protocols is to rely on a secure transport layer to protect messages on the network, and to provide protection against attackers. In order to make the right decision about which secure transport layer protocols to use, and to compare and contrast different secure transport protocols, it is important that we have a good understanding of the properties that they can provide. To do this, we require a means to specify these properties precisely. The aim of this thesis is to improve our understanding of the security guarantees that can be provided by secure transport protocols. We define a framework in which one can capture security properties. We describe a simulation relation over specifications based on the events performed by honest agents. This simulation relation allows us to compare channels; it also allows us to specify the same property in different ways, and to conclude that the specifications are equivalent. We describe a hierarchy of confidentiality, authentication, session and stream properties. We present example protocols that we believe satisfy these specifications, and we describe which properties we believe that the various modes of TLS satisfy. We investigate the effects of chaining our channel properties through a trusted third party, and we prove an invariance theorem for the secure channel properties. We describe how one can build abstract CSP models of the secure transport protocol properties. We use these models to analyse two single sign-on protocols for the internet that rely on SSL and TLS connections to function securely. We present a new methodology for designing security protocols which is based on our secure channel properties. This new approach to protocol design simplifies the design process and results in a simpler protocol.

Voice over IP and video applications continue to increase the amount of traffic over the Internet. These applications utilize the UDP protocol because TCP is not suitable for streaming applications. The flow and congestion control mechanisms of TCP can change the connection transmission rate too drastically, affecting the user-perceived quality of the transmission. Also, the TCP protocol provides a level of reliability that may waste network resources, retransmitting packets that have no value. On the other hand, the use of end-to-end flow and congestion control mechanisms for streaming applications has been acknowledged as an important measure to ease or eliminate the unfairness problem that exist when TCP and UDP share the same congested bottleneck link. Actually, router-based and end-to-end solutions have been proposed to solve this problem. This thesis introduces a new end-to-end protocol based on TCP SACK called SF-SACK that promises to be smooth enough for streaming applications while implementing the known flow and congestion control mechanisms available in TCP. Through simulations, it is shown that in terms of smoothness the SF-SACK protocol is considerably better than TCP SACK and only slightly worse than TFRC. Regarding friendliness, SF-SACK is not completely fair to TCP but considerably fairer than UDP. Furthermore, if SF-SACK is used by both streaming and data-oriented applications, complete fairness is achieved. In addition, SF-SACK only needs sender side modifcations and it is simpler than TFRC.

No description available.

Over the past 15 years, the Internet has proven itself to be one of the most influential inventions that humankind has ever conceived. The success of the Internet can be largely attributed to its stability and ease of access. Among the various pieces of technologies that constitute the Internet, TCP/IP can be regarded as the cornerstone to the Internet’s impressive scalability and stability. Many researchers have been and are currently actively engaged in the studies on the optimization of TCP’s performance in various network environments. This thesis presents an alternative transport layer protocol called RRTP, which is designed to provide reliable transport layer services to software applications. The motivation for this work comes from the fact that the most commonly used versions of TCP perform unsatisfactorily when they are deployed over non-conventional network platforms such as cellular/wireless, satellite, and long fat pipe networks. These non-conventional networks usually have higher network latency and link failure rate as compared with the conventional wired networks and the classic versions of TCP are unable to adapt to these characteristics. This thesis attempts to address this problem by introducing a user-level, reliable, and reconfigurable transport layer protocol that runs on top of UDP and appropriately tends to the characteristics of non-conventional networks that TCP by default ignores. A novel aspect of RRTP lies in identifying three key characteristic parameters of a network to optimize its performance. The single most important contribution of this work is its empirical demonstration of the fact that parameter-based, user-configurable, flow-control and congestion-control algorithms are highly effective at adapting to and fully utilizing various networks. This fact is demonstrated through experiments designed to benchmark the performance of RRTP against that of TCP on simulated as well as real-life networks. The experimental results indicate that the performance of RRTP consistently match and exceed TCP’s performance on all major network platforms. This leads to the conclusion that a user-level, reliable, and reconfigurable transport-layer protocol, which possesses the essential characteristics of RRTP, would serve as a viable replacement for TCP over today’s heterogeneous network platforms.

Over the past 15 years, the Internet has proven itself to be one of the most influential inventions that humankind has ever conceived. The success of the Internet can be largely attributed to its stability and ease of access. Among the various pieces of technologies that constitute the Internet, TCP/IP can be regarded as the cornerstone to the Internet’s impressive scalability and stability. Many researchers have been and are currently actively engaged in the studies on the optimization of TCP’s performance in various network environments. This thesis presents an alternative transport layer protocol called RRTP, which is designed to provide reliable transport layer services to software applications. The motivation for this work comes from the fact that the most commonly used versions of TCP perform unsatisfactorily when they are deployed over non-conventional network platforms such as cellular/wireless, satellite, and long fat pipe networks. These non-conventional networks usually have higher network latency and link failure rate as compared with the conventional wired networks and the classic versions of TCP are unable to adapt to these characteristics. This thesis attempts to address this problem by introducing a user-level, reliable, and reconfigurable transport layer protocol that runs on top of UDP and appropriately tends to the characteristics of non-conventional networks that TCP by default ignores. A novel aspect of RRTP lies in identifying three key characteristic parameters of a network to optimize its performance. The single most important contribution of this work is its empirical demonstration of the fact that parameter-based, user-configurable, flow-control and congestion-control algorithms are highly effective at adapting to and fully utilizing various networks. This fact is demonstrated through experiments designed to benchmark the performance of RRTP against that of TCP on simulated as well as real-life networks. The experimental results indicate that the performance of RRTP consistently match and exceed TCP’s performance on all major network platforms. This leads to the conclusion that a user-level, reliable, and reconfigurable transport-layer protocol, which possesses the essential characteristics of RRTP, would serve as a viable replacement for TCP over today’s heterogeneous network platforms.