Synergy study on charge transport dynamics in hybrid organic solar cell: photocurrent mapping and performance analysis under local spectrum

Charge transport dynamics in ZnO based inverted organic solar cell (IOSC) has been characterized with transient photocurrent spectroscopy and localised photocurrent mapping-atomic force microscopy. The value of maximum exciton generation rate was found to vary from 2.6 × 1027 m−3s−1 (Jsat = 79.7 A m−2) to 2.9 × 1027 m−3s−1 (Jsat = 90.8 A m−2) for devices with power conversion efficiency ranging from 2.03 to 2.51%. These results suggest that nanorods served as an excellent electron transporting layer that provides efficient charge transport and enhances IOSC device performance. The photovoltaic performance of OSCs with various growth times of ZnO nanorods have been analysed for a comparison between AM1.5G spectrum and local solar spectrum. The simulated PCE of all devices operating under local spectrum exhibited extensive improvement with the gain of 13.3–13.7% in which the ZnO nanorods grown at 15 min possess the highest PCE under local solar with the value of 2.82%

Silver nanowires as flexible transparent electrode: role of PVP chain length

In this project, crystalline silver nanowires (AgNWs) are successfully grown using a continuous segmented flow process. The robust relationship among the structural, electrical and optical properties of the AgNWs in the function of the polyvinylpyrrolidone (PVP) chain length is elaborated. A concise carrier transport and a density mechanism are also discussed using a localized conductive atomic force microscopy analysis. The obtained results proved that the AgNWs synthesized using PVP with a chain length of 1.3 M exhibit excellent electrical and optical properties in the form of flexible transparent film with a sheet resistance of 90% at various bending angles. These findings present an alternative approach for production of AgNWs and fabrication of a high flexible transparent electrode

High-resolution X-ray Diffraction Study of Phase and Domain Structures and Thermally-Induced Phase Transformations in PZN-(4.5-9)%PT

Ph.DDOCTOR OF PHILOSOPH

Probing the charge state of threading dislocations in indium nitride through advanced atomic force microscopy

Indium nitride (InN) plays an imperative role in continuing the success of III-nitride technology and extending its footprint into new application fields. However, the development of InN-based devices is hindered by the unusually high residual electron concentration in unintentionally-doped InN, whose origin remains unresolved. In this work, pits are observed at regions around the InN island boundaries, which are assigned to threading dislocations (TDs). Since the surface band bending of InN is found to be intrinsically downward, the positive currents detected exclusively at the InN island boundary regions upon applying positive sample bias are leakage currents. This further points to the presence of TDs in these regions, which can act as localized conductive leakage paths. Interestingly, the surface potentials at the InN island boundary regions are found to be 35–45 mV more positive compared to the InN islands. This can be attributed to the presence of positively charged TDs due to the formation of donor-type point defects along their dislocation cores. Hence, TDs in InN can donate electrons and serve as one of the factors contributing to its high n-type conductivity.</p

Fractal grid-induced turbulence strength characterization via piezoelectric thin-film flapping velocimetry

The centerline streamwise and cross-sectional (x/D(h) = 0.425) turbulence characteristics of a 2D planar space-filling square-fractal-grid (SFG) composed of self-similar patterns superimposed at multiple length-scales is experimentally unveiled via piezoelectric thin-film flapping velocimetry (PTFV). The fluid–structure-interaction between a flexible piezoelectric thin-film and SFG-generated turbulent flow at Re(Dh) = 4.1 × 10(4) is investigated by analysis of the thin-film’s mechanical response. Measurements of the thin-film-tip deflection δ and induced voltage V demonstrate increasing flow fluctuation strength in the turbulence generation region, followed by rapid decay further downstream of the SFG. Interestingly, SFG-induced turbulence enables the generation of maximum centerline thin-film’s response (V(rms), δ(rms)) and millinewton turbulence-forcing (turbulence-induced excitation force acting on the thin-film) F(rms) which are respectively, 7× and 2× larger than the classical square-regular-grid of similar blockage ratio. The low frequency, large-scale energy-containing eddies at SFG’s central opening plays a critical role in driving the thin-film vibration. Most importantly, the SFG-generated turbulence at (y/T = 0.106, z/T = 0.125) away from the centerline allows equivalent mechanical characteristics of turbulence generation and decay, with peak of 1.9× nearer from grid. In short, PTFV provides a unique expression of the SFG-generated turbulence, of which, the equivalent turbulence length-scale and induced-forcing deduced could aid in deciphering the flow dynamics for effective turbulence management

Photocatalytic hydrogen evolution from artificial seawater splitting over amorphous carbon nitride:Optimization and process parameters study via response surface modeling

Photocatalytic water splitting has garnered tremendous attention for its capability to produce clean and renewable H(2) fuel from inexhaustible solar energy. Until now, most research has focused on scarce pure water as the source of H(2), which is not consistent with the concept of sustainable energy. Hence, the importance of photocatalytic splitting of abundant seawater in alleviating the issue of pure water shortages. However, seawater contains a wide variety of ionic components which have unknown effects on photocatalytic H(2) production. This work investigates photocatalytic seawater splitting conditions using environmentally friendly amorphous carbon nitride (ACN) as the photocatalyst. The individual effects of catalyst loading (X(1)), sacrificial reagent concentration (X(2)), salinity (X(3)), and their interactive effects were studied via the Box–Behnken design in response surface modeling towards the H(2) evolution reaction (HER) from photocatalytic artificial seawater splitting. A second-order polynomial regression model is predicted from experimental data where the variance analysis of the regressions shows that the linear term (X(1), X(2)), the two-way interaction term X(1)X(2), and all the quadratic terms (X(12), X(22), X(23)) pose significant effects towards the response of the HER rate. Numerical optimization suggests that the highest HER rate is 7.16 µmol/h, achievable by dosing 2.55 g/L of ACN in 45.06 g sea salt/L aqueous solution containing 17.46 vol% of triethanolamine. Based on the outcome of our findings, an apparent effect of salt ions on the adsorption behavior of the photocatalyst in seawater splitting with a sacrificial reagent has been postulated

Advanced Undersea Warfare Systems

Includes supplementary materialOver the next twenty years, the proliferation of threats in the undersea environment will likely challenge the platform-centric model that the United States Navy uses to maintain dominance in Undersea Warfare (USW). Meanwhile, rapidly maturing technologies offer greater capabilities to potential adversaries around the world. Such a paradigm creates an imperative for the Navy to harness emerging technologies to maintain USW dominance amid a dynamic threat environment, while balancing cost, risk, and required performance. This systems engineering analysis develops Advanced Undersea Warfare Systems (AUWS) that provide a technological and tactical advantage based on the needs of the war-fighter. Following critical analysis of the numerous possible alternatives for performing the necessary Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance (C4ISR) and prosecution and an objective screening process, four system architectures, and associated operational concepts, are selected for detailed analysis. From cost, risk, and performance analyses, superior AUWS concepts are shown to be flexible, scalable, and tailorable systems that balance critical need areas. This analysis highlights the need for new warfare systems that can meet future challenges to the traditional platform-centric model for USW dominance. Using the results and recommendations in this analysis will allow the Navy to deploy capabilities that effectively and efficiently meet future operational needs.http://archive.org/details/advancedundersew109456959Approved for public release; distribution is unlimited

Self-Assembled Heteroepitaxial AuNPs/SrTiO₃: Influence of AuNPs Size on SrTiO₃ Band Gap Tuning for Visible Light-Driven Photocatalyst

Self-assembled heteroepitaxial offers tremendous opportunity to tailor optical and charge transport properties in noble metal–semiconductor interface. Here, we incorporated gold nanoparticles (AuNPs) onto the {001} facets of semiconductor strontium titanate, SrTiO₃ (STO), by means of heteroepitaxial approach to investigate the band gap tuning and its effect of photoresponse. We demonstrate that the Fermi energy level of the system can be tuned by controlling the AuNPs size. X-ray photoelectron spectroscopy (XPS) shows that the energy difference between Sr_3d and Au_4f core levels measured in the AuNPs/STO (100) heterojunction increases from 47.90 to 49.26 eV with decreasing AuNPs size from 65 to 16 nm, respectively. Hence, the Fermi energy level was shifted toward the conductive band of STO (100), and the system charge transfer efficiency was improved. It was also found that smaller AuNPs sizes exhibited a higher photoactivity as the result of the band gap narrowing effect. Photoactivity was improved by broadening the catalyst absorption spectrum to the visible light region. This study provides a basic understanding of the photoelectrochemistry of metal–semiconductor heterostructure for visible light-energy conversion