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Projeto de investigação
Photonic-enhanced Quantum Nano-structured Perovskite Solar Cells
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Understanding the Potential of Light Absorption in Dots-in-Host Semiconductors
Publication . Alexandre, Miguel; Águas, Hugo; Fortunato, Elvira; Martins, Rodrigo; Mendes, Manuel J.; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; ACS - American Chemical Society
The outstanding physical properties of dots-in-host (QD@Host) hetero semiconductors demand detailed methods to fundamentally understand the best routes to optimize their potentialities for different applications. In this work, a 4-band k.p-based method was developed for rock-salt quantum dots (QDs) that describes the complete optical properties of arbitrary QD@Host systems, trailblazing the way for the full optoelectronic analysis of quantum-structured solar cells. Starting with the determination of the QD bandgap and validation against well-established literature results, the electron transition rate is then computed and analyzed against the main system parameters. This is followed by a multiparameter optimization, considering intermediate band solar cells as a promising application, where the best QD configuration was determined, together with the corresponding QD@Host absorption spectrum, in view of attaining the theoretical maximum efficiency (∼50%) of this photovoltaic technology. The results show the creation of pronounced sub-bandgap absorption due to the electronic transitions from/to the quantum-confined states, which enables a much broader exploitation of the sunlight spectrum.
Soft-Microstructured Transparent Electrodes for Photonic-Enhanced Flexible Solar Cells
Publication . Boane, Jenny L. N.; Centeno, Pedro; Mouquinho, Ana; Alexandre, Miguel; Calmeiro, Tomás; Fortunato, Elvira; Martins, Rodrigo; Mendes, Manuel J.; Águas, Hugo; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias
Microstructured transparent conductive oxides (TCOs) have shown great potential as photonic electrodes in photovoltaic (PV) applications, providing both optical and electrical improvements in the solar cells’ performance due to: (1) strong light trapping effects that enhance broadband light absorption in PV material and (2) the reduced sheet resistance of the front illuminated contact. This work developed a method for the fabrication and optimization of wavelength-sized indium zinc oxide (IZO) microstructures, which were soft-patterned on flexible indium tin oxide (ITO)-coated poly(ethylene terephthalate) (PET) substrates via a simple, low-cost, versatile, and highly scalable colloidal lithography process. Using this method, the ITO-coated PET substrates patterned with IZO micro-meshes provided improved transparent electrodes endowed with strong light interaction effects—namely, a pronounced light scattering performance (diffuse transmittance up to ~50%). In addition, the photonic-structured IZO mesh allowed a higher volume of TCO material in the electrode while maintaining the desired transparency, which led to a sheet resistance reduction (by ~30%), thereby providing further electrical benefits due to the improvement of the contact conductance. The results reported herein pave the way for a new class of photonic transparent electrodes endowed with mechanical flexibility that offer strong potential not only as advanced front contacts for thin-film bendable solar cells but also for a much broader range of optoelectronic applications.
SCATMM
Publication . Alexandre, Miguel; Santos, Ivan M.; Martins, Rodrigo; Mendes, Manuel J.; Faculdade de Ciências e Tecnologia (FCT); Ubiquity Press
Ease-of-access to efficient and simple modelling software is fundamental for a broader adoption of these tools in academic, R&D or even industrial contexts. Here, we describe a user-friendly graphical user interface (GUI) termed SCATMM that effectively utilizes the well-known Scattering Matrix Method to determine the reflection, transmission, and absorption of arbitrarily thick stacks of planar layers. This capability connects with a wide range of applications, such as determining layer(s) thickness(es) by fitting with experimentally acquired spectra. This article describes the core development of the mathematical model, followed by a description of the main elements of the GUI. The model is validated through comparison with well-established FDTD simulations of a basic solar cell configuration, yielding a precise match between the resulting absorption spectra. For experimental comparison, the SCATMM tool was used to determine the thickness of a planar layer on a glass substrate, offering an additional example of the method’s application. Here, the determined thickness was paired to profilometry and SEM measurements, providing congruent values with less than 8% of discrepancy.
Photonic-Enhanced Perovskite Solar Cells
Publication . Almeida, Eva; Alexandre, Miguel; Santos, Ivan M.; Martins, Rodrigo; Águas, Hugo; Mendes, Manuel J.; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; ACS - American Chemical Society
The current exponential growth of solar electricity technologies toward consumer-oriented applications, as in building- or vehicle-integrated photovoltaics (B/VIPV), is calling for improved solar cells, not only in cost-effectiveness, but also with better adaptability and aesthetics. Here, using perovskite solar cells (PSCs) as test bed, we demonstrate an unprecedented photonic method to generate any color on a cell layout, while also increasing PV efficiency. To this end, photonic surface features were designed for PSCs, which filled the dual purpose of light-trapping (LT) and modulation of reflected light interference. A variety of geometries, from simple gratings to complex semispheroids, were optically optimized for two of the most challenging colors, magenta and green, while assuring the generation of their maximum feasible photocurrent. The best results corresponded to a current density of 22.07 mA/cm2, obtained for the magenta solar cell with top domes, exhibiting an increase of 6.68%, relative to an optimized planar reference cell. In turn, the same type of geometry was able to generate the leading green cell, with up to 21.40 mA/cm2 (a relative increase of 3.44%). Additionally, the uniformity of the optical output of the optimal solar cells was tested under a range of incident light angles, between 0◦ and 60◦, where the current density suffered relative losses only down to 6.65%.
Copper-Arsenic-Sulfide Thin-Films from Local Raw Materials Deposited via RF Co-Sputtering for Photovoltaics
Publication . Centeno, Pedro; Alexandre, Miguel; Neves, Filipe; Fortunato, Elvira; Martins, Rodrigo; Águas, Hugo; Mendes, Manuel J.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); MDPI AG
The inexorable increase of energy demand and the efficiency bottleneck of monocrystalline silicon solar cell technology is promoting the research and development of alternative photovoltaic materials. Copper-arsenic-sulfide (CAS) compounds are still rather unexplored in the literature, yet they have been regarded as promising candidates for use as p-type absorber in solar cells, owing to their broad raw material availability, suitable bandgap and high absorption coefficient. Here, a comprehensive study is presented on the structural and optoelectronic properties of CAS thin-films deposited via radio-frequency magnetron co-sputtering, using a commercial Cu target together with a Cu-As-S target with material obtained from local resources, specifically from mines in the Portuguese region of the Iberian Pyrite Belt. Raman and X-ray diffraction analysis confirm that the use of two targets results in films with pronounced stoichiometry gradients, suggesting a transition from amorphous CAS compounds to crystalline djurleite (Cu31S16), with the increasing proximity to the Cu target. Resistivity values from 4.7 mΩ·cm to 17.4 Ω·cm are obtained, being the lowest resistive films, those with pronounced sub-bandgap free-carrier absorption. The bandgap values range from 2.20 to 2.65 eV, indicating promising application as wide-bandgap semiconductors in third-generation (e.g., multi-junction) photovoltaic devices.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
OE
Número da atribuição
SFRH/BD/148078/2019