Engineering the reciprocal space for ultrathin GaAs solar cells

III-V solar cells dominate the high efficiency charts, but with significantly higher cost than other solar cells. Ultrathin III-V solar cells can exhibit lower production costs and immunity to short carrier diffusion lengths caused by radiation damage, dislocations, or native defects. Nevertheless, solving the incomplete optical absorption of sub-micron layers presents a challenge for light-trapping structures. Simple photonic crystals have high diffractive efficiencies, which are excellent for narrow-band applications. Random structures a broadband response instead but suffer from low diffraction efficiencies. Quasirandom (hyperuniform) structures lie in between providing high diffractive efficiency over a target wavelength range, broader than simple photonic crystals, but narrower than a random structure. In this work, we present a design method to evolve a simple photonic crystal into a quasirandom structure by modifying the spatial-Fourier space in a controlled manner. We apply these structures to an ultrathin GaAs solar cell of only 100 nm. We predict a photocurrent for the tested quasirandom structure of 25.3 mA/cm$^2$, while a planar structure would be limited to 16.1 mA/cm$^2$. The modified spatial-Fourier space in the quasirandom structure increases the amount of resonances, with a progression from discrete number of peaks to a continuum in the absorption. The enhancement in photocurrent is stable under angle variations because of this continuum. We also explore the robustness against changes in the real-space distribution of the quasirandom structures using different numerical seeds, simulating variations in a self-assembly method

Stress compensation by gap monolayers for stacked InAs/GaAs quantum dots solar cells

In this work we report the stacking of 10 and 50 InAs quantum dots layers using 2 monolayers of GaP for stress compensation and a stack period of 18 nm on GaAs (001) substrates. Very good structural and optical quality is found in both samples. Vertical alignment of the dots is observed by transmission electron microscopy suggesting the existence of residual stress around them. Photocurrent measurements show light absorption up to 1.2 μm in the nanostructures together with a reduction in the blue response of the device. As a result of the phosphorus incorporation in the barriers, a very high thermal activation energy (431 meV) has also been obtained for the quantum dot emission

Strain balanced quantum posts for intermediate band solar cells

In this work we present strain balanced InAs quantum post of exceptional length in the context of photovoltaics. We discuss the general properties of these nanostructures and their impact in the practical implementation of an intermediate band solar cell. We have studied the photocurrent generated by strain balanced quantum posts embedded in a GaAs single crystal, and compared our results with quantum dot based devices. The incorporation of phosphorous in the matrix to partially compensate the accumulated stress enables a significant increase of the quantum post maximum length. The relative importance of tunneling and thermal escape processes is found to depend strongly on the geometry of the nanostructures. tunneling and thermal escape processes is found to depend strongly on the geometry of the nanostructures

Solar cell designs by maximizing energy production based on machine learning clustering of spectral variations

Due to spectral sensitivity effects, using a single standard spectrum leads to a large uncertainty when estimating the yearly averaged photovoltaic efficiency or energy yield. Here we demonstrate how machine learning techniques can reduce the yearly spectral sets by three orders of magnitude to sets of a few characteristic spectra, and use the resulting proxy spectra to find the optimal solar cell designs maximizing the yearly energy production. When using standard conditions, our calculated efficiency limits show good agreement with current photovoltaic efficiency records, but solar cells designed for record efficiency under the current standard spectra are not optimal for maximizing the yearly energy yield. Our results show that more than 1 MWh m−2 year−1 can realistically be obtained from advanced multijunction systems making use of the direct, diffuse, and back-side albedo components of the irradiance.Funding was provided by MINECO (TEC2015-64189-C3-2-R) and Comunidad de Madrid (S2013/MAE-2780). I.G. is funded by Ministerio de Economía y Competitividad (RYC-2014-15621).Peer reviewe

Ether cleavage and chemical removal of SU-8

The high chemical stability of SU-8 makes it irreplaceable for a wide range of applica- tions, most notably as a lithography photoresist for micro and nanotechnology. This advantage becomes a problem when there is a need to remove SU-8 from the fabricated devices. Researchers have been struggling for two decades with this problem, and al- though a number of partial solutions have been found, this difficulty has limited the applications of SU-8. Here we demonstrate a fast, reproducible, and comparatively gen- tle method to chemically remove SU-8 photoresist. An ether cleavage mechanism for the observed reaction is proposed, and the hypothesis is tested with ab initio quantum chem- ical calculations. Also described are a polymer-metal adhesion treatment, and a comple- mentary removal method, based on atomic hydrogen inductively coupled plasma

Structural Origin of Enhanced Luminescence Efficiency of Antimony Irradiated InAs Quantum Dots

We report that Sb irradiation combined with the presence of a GaAs intermediate layer previous to the deposition of a GaSb layer over InAs quantum dots grown by molecular beam epitaxy improves the crystalline quality of these nanostructures. Moreover, this approach to develop III-V-Sb nanostructures causes the formation of quantum dots buried by a confining GaSb layer and, in this way, achieving a type II band alignment. Both phenomena, studied by Conventional transmission electron microscopy (CTEM) and scanning-transmission electron microscope (STEM) techniques are keys to achieve the best room temperature photoluminescence results from InAs/GaAs (001) quantum dots. The Sb flux contributes to the preservation of the quantum dots size and at the same time reduces In diffusion from the wetting layer

Seminario Hegel Complutense 2023-2024. Lectura de "Líneas fundamentales de la filosofía del derecho"

Este proyecto Innova-Docencia pretende consolidar la actividad del Seminario Hegel Complutense para contribuir a la mejora de la calidad de la enseñanza y el aprendizaje universitarios de la filosofía. El proyecto cuenta con 26 docentes provenientes de dos facultades de la UCM (Filosofía y Filología), ocho universidades nacionales (UAM, UNED, UC3M, IE, UFV, UV, UNED, UB) y siete extranjeras de Chile, Holanda, Italia y Macedonia del Norte (UC, PUCV, ISSHS, UniFi, UDP, RUG, UniMi), así como con estudiantes de Grado, Máster y Doctorado de varias facultades de la UCM (Filosofía, Filología, Bellas Artes, Derecho e Historia) y profesores de IES de la Comunidad de Madrid. El seminario nace en junio de 2022 a petición de un grupo de estudiantes de Grado y Máster a la investigadora principal de este proyecto dada la saturación, la fragmentación y los tiempos en ocasiones limitados de los planes de estudios oficiales. El presente proyecto pretende consolidar el Seminario Hegel Complutense para el curso 2023-2024 y siguientes, ofreciendo este curso una lectura de la obra de Hegel Líneas fundamentales de la filosofía del derecho, con la vocación de fundar un punto de encuentro y colaboración entre estudiantes, investigadores y docentes, fortaleciendo competencias relacionadas con el aprendizaje y la investigación, difundiendo sus resultados en colaboración con otros espacios de investigación y/o transferencia del conocimiento y complementando los contenidos de los planes de estudio oficiales (Grado, dobles Grados, Master y Doctorado). La naturaleza participativa del seminario con lectura por grupos y la discusión colectiva ofrece la oportunidad de ensayar metodologías novedosas y enfocadas al alumno. El seminario se enfoca al trabajo con nuevas herramientas digitales y elaboración de materiales en vídeo.Depto. de Filosofía y SociedadDepto. de Lógica y Filosofía TeóricaFac. de FilosofíaFac. de FilologíaFac. de DerechoFac. de Geografía e HistoriaFALSEsubmitte