Planar Thermoelectric Microgenerators Based on Silicon Nanowires

Silicon nanowires have been implemented in microfabricated structures to develop planar thermoelectric microgenerators (??TEGs) monolithically integrated in silicon to convert heat flow from thermal gradients naturally present in the environment into electrical energy. The compatibility of typical microfabrication technologies and the vapor?Cliquid?Csolid (VLS) mechanism employed for silicon nanowire growth has been evaluated. Low-thermal-mass suspended structures have been designed, simulated, and microfabricated on silicon-on-insulator substrates to passively generate thermal gradients and operate as microgenerators using silicon nanowires as thermoelectric material. Both electrical measurements to evaluate the connectivity of the nanowires and thermoreflectance imaging to determine the heat transfer along the device have been employed.     

Charge Generation and Photovoltaic Operation of Solid‐State Dye‐Sensitized Solar Cells Incorporating a High Extinction Coefficient Indolene‐Based Sensitizer

An investigation of the function of an indolene‐based organic dye, termed D149, incorporated in to solid‐state dye‐sensitized solar cells using 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxypheny‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) as the hole transport material is reported. Solar cell performance characteristics are unprecedented under low light levels, with the solar cells delivering up to 70% incident photon‐to‐current efficiency (IPCE) and over 6% power conversion efficiency, as measured under simulated air mass (AM) 1.5 sun light at 1 and 10 mW cm^?2. However, a considerable nonlinearity in the photocurrent as intensities approach “full sun” conditions is observed and the devices deliver up to 4.2% power conversion efficiency under simulated sun light of 100 mW cm^?2. The influence of dye‐loading upon solar cell operation is investigated and the thin films are probed via photoinduced absorption (PIA) spectroscopy, time‐correlated single‐photon counting (TCSPC), and photoluminescence quantum efficiency (PLQE) measurements in order to deduce the cause for the non ideal solar cell performance. The data suggest that electron transfer from the photoexcited sensitizer into the TiO₂ is only between 10 to 50% efficient and that ionization of the photo excited dye via hole transfer directly to spiro‐OMeTAD dominates the charge generation process. A persistent dye bleaching signal is also observed, and assigned to a remarkably high density of electrons “trapped” within the dye phase, equivalent to 1.8 × 10¹⁷ cm^?3 under full sun illumination. it is believed that this localized space charge build‐up upon the sensitizer is responsible for the non‐linearity of photocurrent with intensity and nonoptimum solar cell performance under full sun conditions.     

Analysis of Optical Losses in a Photoelectrochemical Cell: A Tool for Precise Absorptance Estimation

Optical losses in a photoelectrochemical (PEC) cell account for a substantial part of solar‐to‐hydrogen conversion losses, but limited attention is paid to the detailed investigation of optical losses in PEC cells. In this work, an optical model of combined coherent and incoherent light propagation in all layers of the PEC cell based on spectroscopic measurements is presented. Specifically, photoelectrodes using transparent conductive substrates such as F:SnO₂ coated with thin absorber films are focused. The optical model is verified for hematite photoanodes fabricated by atomic layer deposition and successfully used to determine wavelength‐dependent reflection, transmission, layer absorptances, and charge generation rates. Furthermore, the calculated absorptances enable 20–30% more accurate calculations of the absorbed photon‐to‐current efficiency of PEC cells. Our optical model is a powerful tool for the optimization of the optical performance of PEC cells focusing on single absorber or tandem configurations and represents a cornerstone of a complete (optical and electrical) model for PEC water splitting cells.     

Evaluation of registration methods on thoracic CT: the EMPIRE10 challenge

EMPIRE10 (Evaluation of Methods for Pulmonary Image REgistration 2010) is a public platform for fair and meaningful comparison of registration algorithms which are applied to a database of intrapatient thoracic CT image pairs. Evaluation of nonrigid registration techniques is a nontrivial task. This is compounded by the fact that researchers typically test only on their own data, which varies widely. For this reason, reliable assessment and comparison of different registration algorithms has been virtually impossible in the past. In this work we present the results of the launch phase of EMPIRE10, which comprised the comprehensive evaluation and comparison of 20 individual algorithms from leading academic and industrial research groups. All algorithms are applied to the same set of 30 thoracic CT pairs. Algorithm settings and parameters are chosen by researchers expert in the configuration of their own method and the evaluation is independent, using the same criteria for all participants. All results are published on the EMPIRE10 website (http://empire10.isi.uu.nl). The challenge remains ongoing and open to new participants. Full results from 24 algorithms have been published at the time of writing. This paper details the organization of the challenge, the data and evaluation methods and the outcome of the initial launch with 20 algorithms. The gain in knowledge and future work are discussed.     

A Jini service to reconstruct tomographic data

Distributed computing that uses dynamic networks will change the way we work and communicate thanks to the interaction of devices and services, that are automatically added and removed from the network as needed. The Jini technology, which is built atop the Java programming language, provides a homogenous view of the network and extends the ability of code to migrate in Java. This software design model simplifies the configuration and access to hardware devices and software services in a network. Thus, it becomes possible to execute new services without pre-installing software on client machines. This new programming paradigm is especially important in medical applications, where the reliable transmission of information is essential. This paper demonstrates how single photon emission computerized tomography data can be iteratively reconstructed using a Jini service.     

PbS and CdS Quantum Dot‐Sensitized Solid‐State Solar Cells: “Old Concepts,New Results”

Lead sulfide (PbS) and cadmium sulfide (CdS) quantum dots (QDs) are prepared over mesoporous TiO₂ films by a successive ionic layer adsorption and reaction (SILAR) process. These QDs are exploited as a sensitizer in solid‐state solar cells with 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) as a hole conductor. High‐resolution transmission electron microscopy (TEM) images reveal that PbS QDs of around 3 nm in size are distributed homogeneously over the TiO₂ surface and are well separated from each other if prepared under common SILAR deposition conditions. The pore size of the TiO₂ films and the deposition medium are found to be very critical in determining the overall performance of the solid‐state QD cells. By incorporating promising inorganic QDs (PbS) and an organic hole conductor spiro‐OMeTAD into the solid‐state cells, it is possible to attain an efficiency of over 1% for PbS‐sensitized solid‐state cells after some optimizations. The optimized deposition cycle of the SILAR process for PbS QDs has also been confirmed by transient spectroscopic studies on the hole generation of spiro‐OMeTAD. In addition, it is established that the PbS QD layer plays a role in mediating the interfacial recombination between the spiro‐OMeTAD⁺ cation and the TiO₂ conduction band electron, and that the lifetime of these species can change by around 2 orders of magnitude by varying the number of SILAR cycles used. When a near infrared (NIR)‐absorbing zinc carboxyphthalocyanine dye (TT1) is added on top of the PbS‐sensitized electrode to obtain a panchromatic response, two signals from each component are observed, which results in an improved efficiency. In particular, when a CdS‐sensitized electrode is first prepared, and then co‐sensitized with a squarine dye (SQ1), the resulting color change is clearly an addition of each component and the overall efficiencies are also added in a more synergistic way than those in PbS/TT1‐modified cells because of favorable charge‐transfer energetics.     

A New View of Microcrystalline Silicon: The Role of Plasma Processing in Achieving a Dense and Stable Absorber Material for Photovoltaic Applications

To further lower production costs and increase conversion efficiency of thin‐film silicon solar modules, challenges are the deposition of high‐quality microcrystalline silicon (μc‐Si:H) at an increased rate and on textured substrates that guarantee efficient light trapping. A qualitative model that explains how plasma processes act on the properties of μc‐Si:H and on the related solar cell performance is presented, evidencing the growth of two different material phases. The first phase, which gives signature for bulk defect density, can be obtained at high quality over a wide range of plasma process parameters and dominates cell performance on flat substrates. The second phase, which consists of nanoporous 2D regions, typically appears when the material is grown on substrates with inappropriate roughness, and alters or even dominates the electrical performance of the device. The formation of this second material phase is shown to be highly sensitive to deposition conditions and substrate geometry, especially at high deposition rates. This porous material phase is more prone to the incorporation of contaminants present in the plasma during film deposition and is reported to lead to solar cells with instabilities with respect to humidity exposure and post‐deposition oxidation. It is demonstrated how defective zones influence can be mitigated by the choice of suitable plasma processes and silicon sub‐oxide doped layers, for reaching high efficiency stable thin film silicon solar cells.     

Bondability analysis of bond pads by thermoelectric temperature measurements

To reduce cost and enhance reliability for microelectronics applications, a complete understanding of the thermosonic bonding process is required. In particular, the question of whether melting, diffusion, or significant heating occurs along the interface during friction has often been raised. We present results obtained with a new device based on thermoelectric temperature measurements to determine the temperature at the bond interface. In addition to the temperature information, the data characterizes the bonding process in real time on a micrometer scale. The basic principle of the developed apparatus is temperature measurement by an Au-Ni thermocouple fixed within the inside chamfer of a bonding capillary. Different bond substrates with high and low bond contact quality have been investigated. The thermoelectric temperature measurements very precisely determines the bonding behavior of the bond pads. A few nanometers surface contamination on a bond pad significantly reduces the temperature rise at the bond interface and therefore impairs bondability of the substrate. These results demonstrate the sensitivity and accuracy of the measurement principle. The apparatus is a powerful tool to measure the tribology of the bond system and to characterize the bondability of different bond pads.     

Surface Reconstruction Engineering with Synergistic Effect of Mixed-Salt Passivation Treatment toward Efficient and Stable Perovskite Solar Cells

Surface passivation treatment is a widely used strategy to resolve trap-mediated nonradiative recombination toward high-efficiency metal-halide perovskite photovoltaics. However, a lack of passivation with mixture treatment has been investigated, as well as an in-depth understanding of its passivation mechanism. Here, a systematic study on a mixed-salt passivation strategy of formamidinium bromide (FABr) coupled with different F-substituted alkyl lengths of ammonium iodide is demonstrated. It is obtained better device performance with decreasing chain length of the F-substituted alkyl ammonium iodide in the presence of FABr. Moreover, they unraveled a synergistic passivation mechanism of the mixed-salt treatment through surface reconstruction engineering, where FABr dominates the reformation of the perovskite surface via reacting with the excess PbI₂. Meanwhile, ammonium iodide passivates the perovskite grain boundaries both on the surface and top perovskite bulk through penetration. This synergistic passivation engineer results in a high-quality perovskite surface with fewer defects and suppressed ion migration, leading to a champion efficiency of 23.5% with mixed-salt treatment. In addition, the introduction of the moisture resisted F-substituted groups presents a more hydrophobic perovskite surface, thus enabling the decorated devices with excellent long-term stability under a high humid atmosphere as well as operational conditions.