Browsing by Author "Cunha, José M. V."
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- Characterization of the Interfacial Defect Layer in Chalcopyrite Solar Cells by Depth‐Resolved Muon Spin SpectroscopyPublication . Alberto, Helena V.; Vilão, Rui C.; Ribeiro, Eduardo F. M.; Gil, João M.; Curado, Marco A.; Teixeira, Jennifer P.; Fernandes, Paulo A.; Cunha, José M. V.; Salomé, Pedro M. P.; Edoff, Marika; Martins, Maria I.; Prokscha, Thomas; Salman, Zaher; Weidinger, AloisAs devices become smaller and more complex, the interfaces between adjacent materials become increasingly important and are often critical to device performance. An important research goal is to improve the interface between the absorber and the window layer by inserting buffer layers to adjust the transition. Depth-resolved studies are key for a fundamental understanding of the interface. In the present experiment, the interface between the chalcopyrite Cu(In,Ga)Se2 absorber and various buffer layers are investigated using low-energy muon spin rotation (μSR) spectroscopy. Depth resolution in the nm range is achieved by implanting the muons with different energies so that they stop at different depths in the sample. Near the interface, a region about 50 nm wide is detected where the lattice is more distorted than further inside the absorber. The distortion is attributed to the long-range strain field caused by defects. These measurements allow a quantification of the corresponding passivation effect of the buffer layer. Bath-deposited cadmium sulfide provides the best defect passivation in the near interface region, in contrast to the dry-deposited oxides, which have a much smaller effect. The experiment demonstrates the great potential of low energy μSR spectroscopy for microscopic interfacial studies of multilayer systems.
- Cu(In,Ga)Se$$_2$$-based solar cells for space applications: Proton irradiation and annealing recoveryPublication . Candeias, Maria B.; Fernandes, Tiago V.; Falcão, Bruno P.; Cunha, António F.; Cunha, José M. V.; Barbosa, João; Teixeira, Jennifer P.; Fernandes, Paulo A.; Peres, Marco; Lorenz, Katharina; Salomé, Pedro M. P.; Leitão, Joaquim P.In this work, we present an experimental study of a Cu(In,Ga)Se2 (CIGS)-based solar cell (SC), irradiated with protons of energy 80 and 180 keV and with fuences of 1012 , 1013 , and 1014 cm−2 , as well as a strategy to recover the induced damage. The possible modifcations of the structural, electrical, and optical properties, induced by the proton irradiation, were investigated. Although the irradiation did not promote any major modifcation in the crystalline structure, it did induce the creation of defects responsible for changes in the electronic structure which caused a partial PL quenching and signifcant changes in the PL spectral shape, as well as a reduction of the power conversion efciency and open-circuit voltage of up to 30% as revealed by J–V measurements. The photoluminescence results showed a broadening, redshift and decrease in the signal-to-noise ratio. The recovery of damage induced by irradiation in several SCs was tested through annealing steps performed at diferent temperatures and time intervals. It was found that the best recovery strategy for the investigated irradiation parameters was carrying out several isothermal annealing at 200°C for 30 min. This strategy is compatible with the intermitent variation of the temperature in space and allowed to recover a power conversion efciency comparable to that of the as grown cell. In particular, it must be highlighted that keeping the SC at room temperature in ambient atmosphere and in the dark, did not promote signifcant recovery in contradiction with some previous reports. This recovery methodology was applied in parallel for non-irradiated SCs and no increase in power conver sion efciency was found, but rather a slight decrease. The dominant radiative recombination channel was, apparently, unchanged with the irradiation and the subsequent recovery process. Nonetheless, changes in the concentration of defects of diferent types cannot be excluded, which is in line with a signifcant infuence of fuctuating potentials in both as grown and after recovery stages of the solar cell. This work constitutes a frst systematic study that simultaneously encompasses the infuence of proton irradiation on the optical and electrical properties of CIGS SCs and a damage recovery methodology with a high potential to be explored in space applications. Additionally, it contributes to reinforcing the high potential of CIGS technology in the context of creating constellations of small satellites that are being developed by diferent entities, particularly private ones.