Search

Single-crystal chemical vapour deposition (CVD) diamond samples with asymmetric Schottky contacts were used for the fabrication of vertical metal-semiconductor-metal detectors for deep ultraviolet (UV–C) radiation. Spectral photoconductivity measurements, performed in the 190 ÷ 1100 nm wavelength range, returned an ultraviolet-to-visible (UV/Vis) rejection ratio of 6.8 × 103 under photovoltaic operating conditions, ensuring solar blindness and zero power consumption at the same time. When applying bias, UV/Vis rejection ratio reached excellent values (>104) even at very low electric fields (0.01 V/μm), thanks to the excellent structural quality and the superior charge transport properties of the diamond bulk, as inferred from Raman analysis and spectral photoconductivity measurements. Mobility-lifetime (μτ) product of the photogenerated carriers was indeed measured to be about 5 × 10−3 cm2/V in the case of holes, which is the highest room-temperature μτ value ever reported for CVD diamond, enabling a response speed in the nanosecond range even at zero-bias operating conditions. [Display omitted] • The concept of asymmetric Schottky contacts was applied for the first time to diamond UV-Cdetectors. • Self-powered operation was successfully demonstrated even under a weak (3.7 μW/cm2) UV-C light. • Nanosecond-response speed and a linear dynamic range of 80 dB were obtained. • A mobility-lifetime product of 5 × 10−3 cm2/V was measured for holes at room temperature. [ABSTRACT FROM AUTHOR]

• LaB 6 ceramics are proposed as novel double-function solar absorber & thermionic emitter for high-temperature CSP/CST. • Femtosecond laser treatments are used to manipulate the optical properties of ceramic surfaces. • Depending on the laser accumulated fluence, Laser-Induced Periodic Surface Structures (LIPSS) are created. • Under optimal laser processing conditions, solar absorptance increases and at the same time thermal emittance decreases. • This boosts two of the FOMs used to evaluate solar absorbers: spectral selectivity and photothermal efficiency. Lanthanum hexaboride (LaB 6) single-crystals are known from a long time for their excellent thermionic and field-assisted electron-emitting properties. Recently, multi-crystalline ceramics, which offer several technological advantages over single-crystals, have been studied as well, proving a low work function and Richardson constant, in addition to favorable optical properties for high-temperature solar radiation absorbers. However, to fully disclose to LaB 6 ceramics the novel application of a double-function bulk thermionic emitter, enabled by the direct absorption of solar radiation, and, at the same time, thermodynamic solar absorber for Concentrating Solar Power (CSP), their optical properties should be further optimized. The ideal result, consisting in the selective increase of the solar absorptance and decrease of the thermal emittance, thus increasing both the spectral selectivity and the photothermal efficiency of the absorber, has been obtained in this work by realizing Laser-Induced Periodic Surface Structures (LIPSS) on the ceramic surface by means of femtosecond-laser treatments. LIPPS formation has been investigated as a function of the accumulated laser fluence. [ABSTRACT FROM AUTHOR]

Abstract Surface nanostructured diamond films by ultrashort pulse laser treatment, named black diamond, demonstrated a huge increase in the photogeneration capability for photons with sub-bandgap energy (<5.47 eV). Here we analyze in detail the transport properties of photogenerated charge carriers in several black diamond samples, in order to better understand the electronic behavior of defect levels introduced by the laser treatment. If compared with the pristine diamond films, the mean charge carriers' mobility-lifetime product, evaluated from the over bandgap photocurrent characteristics, remarkably increases in every black diamond set up to a defined absorbed accumulated laser fluence before decreasing at the highest fluence values. We attribute this effect to the laser-induced introduction of fast traps for one charge carrier type, that increases with fluence. At the same time, an increasing density of recombination centers, capturing permanently the charge carriers, is formed. A trade-off treatment condition can be found in order to maximize the sensitivity to sub-bandgap photons and the mean mobility-lifetime product as well as to limit the effect of recombination centers. [ABSTRACT FROM AUTHOR]

Graphite conductive vertical microchannels, fabricated by femtosecond laser treatment, are proposed as distributed electrodes in defect-engineered (“black”) single-crystal diamond cathodes for innovative solar cells. Energy conversion is based on photon-enhanced thermionic emission, where the reduction of the cathode series resistance is crucial to preserve conversion efficiency. Process yield higher than 80% and resistivity as low as 0.75 ± 0.15 Ω cm were achieved by the optimization of laser parameters and the use of a multi-pass writing technique. A 100 × 100 array of graphite electrodes was integrated in a diamond-based cathode prototype, reducing the series resistance of more than 10 orders of magnitude with respect to bulk diamond. [ABSTRACT FROM AUTHOR]

Black diamond is obtained by a controlled nanoscale periodic texturing of CVD diamond surface, able to drastically modify the interaction with solar radiation from optical transparency up to solar absorptance values even >90%. Surface texturing, performed by the use of an ultra-short pulse laser, is demonstrated to induce an intermediate band within the diamond bandgap supporting an efficient photoelectronic conversion of sub-bandgap photons (<5.5 eV). The intermediate band introduction results in an external quantum efficiency enhanced up to 800 nm wavelengths (and up two orders of magnitude larger than the starting transparent diamond film), without affecting the film transport capabilities. The optical and photoelectronic outstanding results open the path for future application of black diamond as a photon-enhanced thermionic emission cathode for solar concentrating systems, with advantages of excellent electronic properties combined with a potentially very low work function and high thermal stability. [ABSTRACT FROM AUTHOR]

• Development of a one-dimensional code for the simulation of thermophotovoltaics. • The code can reveal the optimal characteristic parameters of such systems. • Parametric analysis of various operating conditions and semiconductor materials. • An interpolation algorithm of the calculated efficiencies has been built. • This algorithm can be coupled with a CFD model to evaluate the device performance. During the last years, innovative concepts of solid-state devices, such as multi-junction solar cells and thermophotovoltaic converters, have emerged as efficient means of direct electricity production. The accurate estimation of the conversion efficiency of such devices using simple yet effective numerical tools is a necessity to optimize their performance. This work presents an in-house code, which is based on the Drift Diffusion Model to simulate p-n junction diodes, under equilibrium (bias voltage application) and non-equilibrium (bias voltage and device illumination) conditions. Under non-equilibrium, illumination can originate from either solar radiation (conventional photovoltaic cell) or a thermally heated emitter (thermophotovoltaic operation). The drift-diffusion and Poisson's equations are solved using a one-dimensional (1D) finite element Petrov-Galerkin method based on piecewise nonlinear interpolants of second-order accuracy, while the total current is evaluated in a post-process manner using the Scharfetter-Gummel scheme. Initially, the model is verified against the freeware SimWindows. Later on, a parametric analysis on the photovoltaic cell design and operating conditions reveals that its efficiency is highly affected by its total length, the n-type sub-region width, the doping levels of both p and n regions, the semiconductor material type, and, the device's operating temperature. In contrast to other solvers, this one takes into account the model parameters' dependence on temperature and electromagnetic spectrum, while it can be extended to incorporate the thermally stimulated electron emission in thermionic-based devices and 2D spatial effects. Finally, the calculated conversion efficiencies can be used to build a Reduced Order Model that can be further coupled with a computational fluid dynamics model to evaluate the overall thermo-electric performance of a solid-state device. [ABSTRACT FROM AUTHOR]

• We studied air exposed hydrogenated diamond. • We performed conductance measurements as a function of time and temperature. • We carried out density functional theory calculations. • We estimated the desorption energy per water molecule. • We estimated the interface charge transfer. The air-exposed hydrogenated diamond surface has been studied by carrier transport measurements and density functional theory. Our results have allowed us to understand the close relationship between the physisorbed water molecules and the electrical resistance. We have therefore been able to show that the evolution of the resistance over time and temperature can be related to the extent of the hole accumulation layer originating at the surface of the hydrogenated diamond. The method has allowed us to estimate the desorption energy of a single water molecule by means of resistance measurements alone. [ABSTRACT FROM AUTHOR]