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The highest efficiencies in single-junction solar cells are obtained with devices based on GaAs. As this material is reaching the limit in material quality, the optimization of the design of the cell becomes more important. In this study we implement a patterning technique to the bottom contact layer of thin-film GaAs solar cells that increases the reflectance of photons to the active layers. Both shallow junction and deep junction devices were evaluated, and for deep junction cells, both the short circuit current and the open circuit voltage increase with the reflectance. The radiative saturation current density also decreases, indicating increased photon recycling. Detailed model simulations are performed to further evaluate the mechanisms leading to the improved performance of the deep junction design. Based on the same model, the possibilities for further improvements utilizing the deep junction are also identified.

We report thin-film InAs/GaAs quantum dot (QD) solar cells with n − i − p + deep junction structure and planar back reflector fabricated by epitaxial lift-off (ELO) of full 3-in wafers. External quantum efficiency measurements demonstrate twofold enhancement of the QD photocurrent in the ELO QD cell compared to the wafer-based QD cell. In the GaAs wavelength range, the ELO QD cell perfectly preserves the current collection efficiency of the baseline single-junction ELO cell. We demonstrate by full-wave optical simulations that integrating a micro-patterned diffraction grating in the ELO cell rearside provides more than tenfold enhancement of the near-infrared light harvesting by QDs. Experimental results are thoroughly discussed with the help of physics-based simulations to single out the impact of QD dynamics and defects on the cell photovoltaic behavior. It is demonstrated that non radiative recombination in the QD stack is the bottleneck for the open circuit voltage ( V oc ) of the reported devices. More important, our theoretical calculations demonstrate that the V oc offset of 0.3 V from the QD ground state identified by Tanabe et al., 2012, from a collection of experimental data of high quality III-V QD solar cells is a reliable – albeit conservative – metric to gauge the attainable V oc and to quantify the scope for improvement by reducing non radiative recombination. Provided that material quality issues are solved, we demonstrate – by transport and rigorous electromagnetic simulations – that light-trapping enhanced thin-film cells with twenty InAs/GaAs QD layers reach efficiency higher than 28% under unconcentrated light, ambient temperature. If photon recycling can be fully exploited, 30% efficiency is deemed to be feasible.

This paper presents an experimental and theoretical study on the impact of doping and recombination mechanisms on quantum dot solar cells based on the InAs/GaAs system. Numerical simulations are built on a hybrid approach that includes the quantum features of the charge transfer processes between the nanostructured material and the bulk host material in a classical transport model of the macroscopic continuum. This allows gaining a detailed understanding of the several physical mechanisms affecting the photovoltaic conversion efficiency and provides a quantitatively accurate picture of real devices at a reasonable computational cost. Experimental results demonstrate that QD doping provides a remarkable increase of the solar cell open-circuit voltage, which is explained by the numerical simulations as the result of reduced recombination loss through quantum dots and defects.

The study presents a theoretical investigation of the impact of individual electron and hole dynamics on the photovoltaic characteristics of InAs/GaAs quantum dot solar cells. The analysis is carried out by exploiting a model which includes a detailed description of quantum dots (QD) kinetics within a drift-diffusion formalism. Steady-state and transient simulations show that hole thermal spreading across the closely spaced QD valence band states allows to extract the maximum achievable photocurrent from the QDs; on the other hand, slow hole dynamics turns QDs into efficient traps, impairing the short circuit current despite the extended light harvesting provided by the QDs.

We report thin-film InAs/GaAs QD solar cells fabricated by epitaxial lift-off of 3-inch wafers containing QD epi-structures with high in-plane QD density. External quantum efficiency measurements demonstrate enhanced QD harvesting in the thin-film configuration. Numerical simulations show that remarkably high increase of the QD photocurrent may be achieved by replacing the planar rear mirror with micro-structured photonic gratings. Measurements of diffraction efficiency of grating prototypes realized on GaAs wafers by nanoimprint lithography are presented.

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 a theoretical study of the effect of the nature of the carrier escape from quantum dots (QDs) on the performance of InAs/GaAs QD solar cells (QDSCs), based on numerical simulations. Excitonic and non-excitonic dynamics of electrons and holes are considered in the modeling, by assuming identical or separate time constants for the intersubband carrier transfer processes in the ground and excited states. It is shown that the excitonic capture and escape allow us to explain the non-additive characteristic of the QD photocurrent, observed when the total photocurrent of the cell is much lower than the sum of the photocurrents contributed separately by the barrier and the nanostructures. This behavior is practically eliminated in the non-excitonic case. The correlated dynamics under the non-excitonic scenario is analyzed by calculating the device sensitivity to small changes introduced in the escape time of electrons. It is stated that the non-variation of the QD photocurrent with this parameter could be interpreted as a consequence of either a correlated electron-hole escape from QDs, or a dominant recombination over the other involved processes. The ideality factor of the different QDSCs studied is also calculated from simulations under both concentrated sunlight and dark conditions. The obtained results are in line with experimental measurements published in the literature.

An iterative method based on numerical simulations was developed to enhance the proton radiation tolerance and the responsivity of Si PIN photodiodes. The method allows to calculate the optimal values of the intrinsic layer thickness and the incident light wavelength, in function of the light intensity and the maximum proton fluence to be supported by the device. These results minimize the effects of radiation on the total reverse current of the photodiode and maximize its response to light. The implementation of the method is useful in the design of devices whose operation point should not suffer variations due to radiation.

This paper presents a theoretical study about quantum dot solar cells by means of numerical simulations, considering different doping levels in the intrinsic region of the cells, with the aim of evaluating the effect on the device's power conversion efficiency. Results of simulations performed over GaAs solar cells with InAs quantum dots, based on two different fabrication processes, are reported. The donor doping density in the intrinsic region was ranged from 1013 to 1017 cm-3. It is shown that, for a doping level of 7×1015 cm-3, the contribution of larger sized quantum dots to the photocurrent is increased by 50%, a very promising result in the search for new designs with higher efficiencies. Fil: Cedola, Ariel Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ingeniería. Departamento de Electrotecnia. Grupo de Est.s/materiales y Disposit.electronicos; Argentina Fil: Gioannini, Mariangela. Politecnico di Torino; Italia Fil: Cappelluti, Federica. Politecnico di Torino; Italia Fil: Cappelletti, Marcelo Ángel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ingeniería. Departamento de Electrotecnia. Grupo de Est.s/materiales y Disposit.electronicos; Argentina Fil: Peltzer y Blanca, Eitel Leopoldo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ingeniería. Departamento de Electrotecnia. Grupo de Est.s/materiales y Disposit.electronicos; Argentina

The radiation resistance in InGaP/GaAs/Ge triple-junction solar cells is limited by that of the middle GaAs sub-cell. In this work, the electrical performance degradation of different GaAs sub-cells under 1 MeV electron irradiation at fluences below 4 × 1015 cm−2 has been analyzed by means of a computer simulation. The numerical simulations have been carried out using the onedimensional device modeling program PC1D. The effects of the base and emitter carrier concentrations of the p- and n-type GaAs structures on the maximum power point have been researched using a radiative recombination lifetime, a damage constant for the minority carrier lifetime and carrier removal rate models. An analytical model has been proposed, which is useful to either determine the maximum exposure time or select the appropriate device in order to ensure that the electrical parameters of different GaAs sub-cells will have a satisfactory response to radiation since they will be kept above 80% with respect to the non-irradiated values. Fil: Cappelletti, Marcelo Ángel. Universidad Nacional Arturo Jauretche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ingeniería. Departamento de Electrotecnia; Argentina Fil: Cedola, Ariel Pablo. Universidad Nacional de La Plata. Facultad de Ingeniería. Departamento de Electrotecnia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina Fil: Peltzer y Blanca, Eitel Leopoldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ingeniería. Departamento de Electrotecnia; Argentina

A theoretical study of the electrical performance of p-on-n GaAs sub-cells under AM0, irradiated with 1 MeV electrons, has been carried out by means of computer simulation. Effects of both base and emitter carrier concentration upon radiation resistance of these devices have been researched. From analysis it is possible to determine the highest electron fluence to which the electrical parameters of the solar cell, with well-known base and emitter carrier concentrations, are reduced simultaneously in less than 20% from their non-irradiated values. Results presented in this paper are important in order to contribute to the design of radiation-hardened devices.

In this paper, we present a study about Si and GaAs space solar cells by means of numerical simulations. We have investigated the variations of the short-circuit current, open circuit voltage and maximum power point, before and after the devices were irradiated with 10 MeV protons and fluences between 109 and 1013 p+ /cm2. The simulation results allow to obtain the optimum solar cell with specific requirements for space applications. Fil: Cappelletti, Marcelo Ángel. Universidad Nacional de La Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Casas, Guillermo. Universidad Nacional de La Plata; Argentina. Universidad Nacional de Quilmes; Argentina Fil: Cedola, Ariel Pablo. Universidad Nacional de La Plata; Argentina Fil: Peltzer y Blanca, Eitel Leopoldo. Universidad Nacional de La Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

An iterative method applied to enhance the proton radiation tolerance and the responsivity of PIN photodiodes was developed. The method allows to calculate optimal values of the intrinsic layer thickness and the incident light wavelength, in function of the light intensity and the maximum proton fluence to be supported by the device. These results minimize the effects of radiation on the total reverse current of the photodiode and maximize its response to light. The implementation of the method is useful in the design of devices that will not suffer variations from its operation point due to radiation.

In the present work, a complete numerical analysis of the influence of deep-trap levels on the dark current of silicon PIN photodiodes under 1 MeV neutron radiation was done. Results corroborate that energy levels near the mid-gap affect to a great extent the dark current. Radiation tolerances of undoped and gold-doped devices were compared through simulations. It has been concluded that gold in silicon reduces the neutron-induced damage. Finally, a model to calculate the dark current of irradiated devices doped with deep-impurities is presented.

This work focuses on study of radiation induced displacement damage effects on silicon PIN photodiodes at both, dark and illumination conditions, by mean of numerical simulations. For fluences greater than a certain limiting value, relation between photocurrent and dark current decreases below ten, leading to an undesirable device operation. An iterative method is proposed for design optimization of PIN photodiodes to be used under irradiation, that minimize radiation effects on total reverse current and maximize device response to incident light.

The experimental evolution of the threshold voltage of MOS devices during irradiation at changing bias voltages, exhibiting charging and neutralization of the oxide traps, was well fitted by a two-traps dynamic balance model. The values and field dependence of the extracted physical parameters are in close agreement with previously reported ones.

A computer program for the simulation of semiconductor devices has been developed and applied to the analysis of radiation effects on Si PIN photodiodes. The study has allowed the authors to propose useful analytical models related to such optical and electrical device parameters as peak spectral response and dark current. Peak spectral response has shown a marked dependence on device layers dimensions. Dark current has demonstrated linear increase with intrinsic layer length and proton-radiation fluence. But the most important obtained result has been the determination of a particular set of semiconductor P-, I- and N-layer thicknesses, for given values of total device length and incident light intensity, that minimize radiation effects during photodiode operation in space environments up to high particle fluences.