Assessment of thermal instabilities and oscillations in multifinger heterojunction bipolar transistors through a harmonic-balance-based CAD-oriented dynamic stability analysis technique

We present a novel analysis of thermal instabilities and oscillations in multifinger heterojunction bipolar transistors (HBTs), based on a harmonic-balance computer-aided-design (CAD)-oriented approach to the dynamic stability assessment. The stability analysis is carried out in time-periodic dynamic conditions by calculating the Floquet multipliers of the limit cycle representing the HBT working point. Such a computation is performed directly in the frequency domain, on the basis of the Jacobian of the harmonic-balance problem yielding the limit cycle. The corresponding stability assessment is rigorous, and the efficient calculation method makes it readily implementable in CAD tools, thus allowing for circuit and device optimization. Results on three- and four-finger layouts are presented, including closed-form oscillation criteria for two-finger device

Physical simulation of perovskite/silicon three-terminal tandems based on bipolar transistor structure

Tandem solar cells made of organometal halide perovskite and crystalline silicon cells are one of the most promising routes towards high eciency low cost photovoltaics. Among the possible architectures, monolithic three-terminal tandems hold the promise of the highest energy/cost gure of merit, by combining the advantage of two- and four-terminal approaches. Recently, three-terminal perovskite/silicon tandems have been reported, based on interdigitated back contact heterojunction silicon cells. Alternative solutions that can be integrated with double-sided contact silicon cells are worth to be investigated in view of their higher compatibility with industrial mass production. In this work, we present a simulation-based proof-of-concept of PVK/Si threeterminal tandem cells that use a heterostructure bipolar transistor structure. The extra terminal is implemented at the common selective layer between the perovskite and silicon subcells, avoiding the use of any recombination layer or tunneling junction. We demonstrate promising device performance through physics-based simulations preliminarily validated against experimental data of other perovskite/silicon tandem technologies reported in literature

Database of optical parameters for the simulation of perovskite/silicon solar cells

This dataset contains a set of representative optical parameters, i.e. the wavelength dependent complex refractive index (n+ik), for common materials used in perovskite-silicon tandems. In particular: SnO2, Spiro-MEOTAD, CH3NH3PbI2, a-Si:H, undoped c-Si, MgF. The data are stored in the ASCII file “nk_MaterialParameters.txt”, where for each material, we report three data columns: wavelength (in µm), refractive index n and extinction coefficient k

Co-creating FAIR data standards with professional associations in Engineering disciplines: Can it accelerate FAIR awareness and adoption in engineering disciplines?

Paper associated with the lightning talk of the title above during the "FAIR and metadata" parallel session during IDCC202

Impact of doping on InAs/GaAs quantum-dot solar cells: A numerical study on photovoltaic and photoluminescence behavior

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

Open Circuit Voltage Recovery in Quantum Dot Solar Cells: a Numerical Study on the Impact of Wetting Layer and Doping

The authors present a numerical study on the influence of wetting layer states and doping on the photovoltage loss of InAs/GaAs quantum dot solar cells. Quantum-mechanical simulations are used to analyse how the reduction of wetting layer by Al(Ga)As overgrowth changes the quantum dot electronic states. Device-level simulations allow to correlate such changes with the achievable open circuit voltage. Almost full open circuit voltage recovery is predicted by combining wetting layer reduction, to realise thermal decoupling of barrier and quantum dot confined states, and doping to suppress radiative recombination through the quantum dot confined states

Guided-mode resonance gratings for enhanced mid-infrared absorption in quantum dot intermediate-band solar cells

Achieving strong absorption of low-energy photons is one of the key issues to demonstrate quantum dot solar cells working in the intermediate band regime at practical concentration factors and operating temperatures. Guided-mode resonance effects may enable large enhancement of quantum dot intraband optical transitions. We propose quantum dot thin-film cells designed to have significant field waveguiding in the quantum dot stack region and patterned at the rear-side with a sub-wavelength diffraction grating. Remarkable increase of the optical path length at mid-infrared wavelengths is shown owing to guided-mode resonances. Design guidelines are presented for energy and strength of the second-photon absorption for III-V quantum dots, such as InAs/GaAs and GaSb/GaAs, whose intraband and intersubband transitions roughly extends over the 2 − 8 µm range. The proposed design can also be applied to quantum dot infrared detectors. Angle-selectivity is discussed in view of applications in concentrator photovoltaic systems and infrared imaging systems