Sponge-like nanostructured ZnO layers were successfully employed as photoanodes for the fabrication of highly efficient dye-sensitized solar cells. The sponge-like ZnO layers were obtained by room temperature radio-frequency magnetron sputtering deposition of metallic zinc, followed by thermal oxidation treatment in an ambient atmosphere. The porous films show a 3D branched nanomorphology, with a feature similar to natural coral. The morphological and optical properties of these layers were studied through field emission scanning electron microscopy, specific surface area measurements, ultraviolet–visible transmittance and absorption spectroscopy. The sponge-like ZnO film presents a high density of branches, with a relatively high specific surface area value, and fine optical transmittance. The morphology of the porous structure provides a high number of adsorption sites for the anchoring of sensitizer molecules, making it suitable for the fabrication of ZnO-based photoanodes for dye-sensitized solar cells. The light harvesting performance of the sensitized semiconductor was evaluated by current density vs. voltage measurements, incident photon-to-electron conversion efficiency, open circuit voltage decay and impedance spectroscopy. The modelling of the electrical characteristics evidences a higher electron lifetime and a longer charge diffusion length, if compared to standard TiO₂ nanoparticle based photoanodes. For ZnO films with a thickness up to 18 μm, a photoconversion efficiency as high as 6.67% and a maximum value of the incident photon-to-electron collection efficiency equal to 87% at 530 nm were demonstrated.

TiO₂ nanotube (NT) arrays with different lengths were fabricated by anodic oxidation of Ti foil and free-standing NT membranes were detached by the metal substrate and bonded on the fluorine-doped tin oxide surface implementing an easy procedure. Morphology of the as-grown material and of the prepared photoanode was investigated by means of electron microscopy, deepening the investigation on the thermal treatment effect. Crystalline orientation and exposed surface area were studied by X-ray diffraction and Brunauer–Emmett–Teller measurements, showing suitable characteristics for the application in dye-sensitized solar cells (DSCs). DSCs were assembled employing a microfluidic housing system. The cell performances and the electron transport properties as a function of the tube length, before and after a TiCl₄ treatment, were characterized by I–V electrical measurements, incident photon-to-electron conversion efficiency, electrochemical impedance spectroscopy and open circuit voltage decay. Fitting the impedance spectra with an equivalent circuit, it was possible to obtain information on the electron diffusion properties into the TiO₂ nanotubes. A comparison with the charge transport properties evaluated in nanoparticle-based photoanodes witnesses a noteworthy increase of electron lifetime and diffusion length, yielding an overall power conversion efficiency up to 7.56%.

This paper presents a device-level model of quantum dot (QD) solar cells, coupling the classical drift-diffusion equations for transport of bulk carriers with a set of rate equations describing the QD carrier dynamics. The model is applied to carry out a detailed study of the impact of thermal-assisted processes on the electrical performance of InAs/GaAs QD solar cells (QDSCs), by exploiting experimentally determined parameters for QD photogeneration and carrier kinetics. Special emphasis is given on the analysis of the open circuit voltage degradation, as well as its dependence on QD size and carrier lifetime. The modeling approach is validated by comparing simulated trends against experimental data in the literature.

This paper presents an accurate and flexible approach to the self-consistent electrothermal modeling of III-N-based HEMTs, combining a temperature-dependent electrical compact model with a novel behavioral nonlinear dynamic thermal model, suitable for circuit-level simulations. The behavioral thermal model is extracted, according to a Wiener-like approach, from a full-scale, finite-element-method-based time-domain 3-D solution of the heat equation. The electrothermal model, validated against dc, pulsed dc, -parameter and large-signal nonlinear measurements, is exploited to assess the impact of thermal memory effects on the device RF performances. In particular, the model allows for a detailed analysis and interpretation of the thermal memory effects on intermodulation distortion. Finally, the proposed approach enables to analyze such features for different thermal mountings, thus providing useful indications for technology assessment.

We investigate the effect of doping on quantum dot (QD) solar cells by analysing their behavior in terms of photovoltaic characteristic, external quantum efficiency, and photoluminescence (PL) at room temperature. The analysis addresses the two most widespread methods for QD selective doping, namely modulation and direct doping, to gain a comprehensive device-level assessment of the impact of doping profile and density on the solar cell behavior. Devices are simulated using a physics-based model that accurately describes QD carrier dynamics within a semi-classical drift-diffusion-Poisson model. Different scenarios in terms of crystal quality are considered: in the high-quality material, close to radiative limit, large open circuit voltage recovery is predicted, due to the suppression of radiative recombination through QD ground state. In the defective material, significant photovoltage recovery is also attained owing to the suppression of both nonradiative and QD ground state radiative recombination. In both cases, PL emission from extended wetting layer states becomes dominant at high doping density. The interplay between nonradiative and QD radiative recombination channels, and how their interaction is modified by doping, are analyzed in detail. Strong influence on the cell behavior of unintentional background doping of interdot layers and markedly nonlinear behavior of open circuit PL with respect to excitation intensity are demonstrated. The resulting picture provides new insight on the experimental results in literature

The effects of electron irradiation on the performance of GaAs solar cells with a range of architectures is studied. Solar cells with shallow and deep junction designs processed on the native wafer as well as into a thin‐film were irradiated by 1‐MeV electrons with fluence up to 1×10¹⁵ e⁻/cm². The degradation of the cell performance due to irradiation was studied experimentally and theoretically using model simulations, and a coherent set of minority carriers' lifetime damage constants was derived. The solar cell performance degradation primarily depends on the junction depth and the thickness of the active layers, whereas the material damage shows to be insensitive to the cell architecture and fabrication steps. The modeling study has pointed out that besides the reduction of carriers lifetime, the electron irradiation strongly affects the quality of hetero‐interfaces, an effect scarcely addressed in the literature. It is demonstrated that linear increase with the electron fluence of the surface recombination velocity at the front and rear hetero‐interfaces of the solar cell accurately describes the degradation of the spectral response and of the dark current characteristic upon irradiation. A shallow junction solar cell processed into a thin‐film device has the lowest sensitivity to electron radiation, showing an efficiency at the end of life equivalent to 82% of the beginning‐of‐life efficiency.