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Projeto de investigação
Tandem Solar Cells Improved Optically
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Optimization of Self-Assembled Particle Deposition for Colloidal Lithography Nano/Micro-Patterning
Publication . Oliveira, Rui Daniel de; Mendes, Manuel; Águas, Hugo
Colloidal lithography (CL) is nowadays considered a preferential nano/micro-patterning
method for photovoltaic structuring, as it is an inexpensive and highly scalable soft-lithography
technique allowing nanoscale precision over indefinitely large areas. Photonic wavelength-sized
structures are on the top of the list of solutions that can boost photovoltaic performance
without significantly increasing cost, as they enable pronounced broadband anti-reflection, LT
effects, and even self-cleaning functionality. In particular, recent research suggested that these
micro-structures can boost not only the efficiency but also the stability of the emergent
perovskite solar cell technology.
CL methods critically depend on the long-range ordered self-assembly that can be
attained upon deposition of the particles’ array used as a mask, which is performed via the
Langmuir-Blodgett method. However, it is still challenging to achieve the desired deposition
quality particularly with the preferential polystyrene colloids with wavelength-scale dimensions.
This thesis is focused on tackling this challenge and in the optimization of the self-assembly
deposition of polystyrene nanospheres monolayers onto flexible substrates, as a part of a full
CL method for photonic-enhancement purposes in thin-film solar cells.
In this work, we report a breakthrough in our Langmuir-Blodgett (LB) method which
prevents wavelength-sized particles from sinking into the aqueous sub-phase and spontaneously
form the desired close-packed hexagonal monolayer. This was attained by using sodium dodecyl
sulfate (SDS) to reduce the aqueous sub-phase surface tension and hence improve the air-water
interface stability of polystyrene spheres of various diameters. The addition of SDS, with best
results at 4.5 mg/l concentration, showed remarkable improvement on the self-assembly step,
by avoiding the nanospheres sinking and by producing uniform high-quality monolayer films.
The quality of the deposition was also improved by controlling the LB barrier closing rate and
increasing the self-assembly work area, which resulted in fully patterned flexible substrates.
High-performance wide bandgap perovskite solar cells fabricated in ambient high-humidity conditions
Publication . Menda, Ugur Deneb; Ribeiro, Guilherme; Nunes, Daniela; Calmeiro, Tomás; Águas, Hugo; Fortunato, Elvira; Martins, Rodrigo; Mendes, Manuel J.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; RSC - Royal Society of Chemistry
Lead-halide perovskite solar cells (PSCs) are currently the most promising emergent thin-film photovoltaic technology, having already reached power conversion efficiency (PCE) levels of state-of-the-art wafer-based silicon cells. The class of wide bandgap PSCs has also demonstrated high PCE values, thus becoming highly attractive for top sub-cells in tandem devices constructed with silicon or other types of bottom sub-cells. In this study, wide bandgap double-halide (Cs0.17FA0.83PbI3-xBrx) perovskite absorbers were developed with different bromine content, aiming to obtain bandgap values between 1.66 to 1.74 eV, by a glovebox-free (ambient) procedure. Low-cost inorganic materials, i.e. TiO2 and CuSCN, were used for the electron and hole transport layers, respectively. The 1.70 eV bandgap perovskite resulted in the highest reproducibility and stability (>80% initial PCE after 3500 hours) properties of the PSCs, remarkably attaining 16.4% PCE even with ambient and high humidity (∼70%) fabrication conditions. This journal is
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.
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
3599-PPCDT
Número da atribuição
PTDC/NAN-OPT/28837/2017