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Effective defect passivation of semiconductor surfaces and interfaces is indispensable for the development of high efficiency solar cells. In this study we systematically investigated the surface and grain boundary properties of CuInSe2 (CISe) with scanning tunneling microscopy (STM) and spectroscopy (STS) after different surface treatments such as potassium cyanide (KCN) etching, pre-electrolyte treatment with cadmium ions, and annealing in ultrahigh vacuum (UHV). We show that air exposed samples with a subsequent KCN etching step exhibits a highly defective surface. However, a Cd pre-electrolyte treatment passivates most of these defects, which manifests itself by a reduction of the high conductance in the STS measurements at positive sample biases. The origin of the improvement can be traced back to an increase in surface band bending, which leads to a type inversion, induced by a change in the concentration of Cu vacancies. We observe a defect passivation at the CISe surface and at the grain boundaries. Our results give a direct explanation of why the CdS buffer layer in CISe thin film solar cells is of utmost importance for high efficiency devices.

Thin-film solar cells consist of several layers. The interfaces between these layers can provide critical recombination paths and consequently play a vital role in the efficiency of the solar cell. One of the main challenges for polycrystalline semiconductor absorber materials is the absorber-buffer interface. The Cu(In,Ga)Se2 system is particularly interesting in this context, since Cu-rich absorbers are dominated by recombination at the interface, while Cu-poor ones are not. This paper unveils the root cause of the challenge in the interface of Cu-rich solar cells in terms of a Se-related defect with an activation energy of 200±20meV. This defect causes interface recombination and is responsible for the deficiency of open-circuit voltage in Cu-rich cells. Moreover, this paper demonstrates that the origin of this defect is due to the etching step necessary to remove secondary phases. Postdeposition surface treatments or modified buffer layers are shown to passivate this defect, to reduce interface recombination, and to increase the efficiency.

Recent progress in the power conversion efficiency of Cu(In,Ga)Se2 thin film solar cells has been achieved by an alkali postdeposition treatment. This treatment has been shown to change the surface composition and structure as well as the bulk properties. To investigate the relative importance of those two effects we study the impact of the treatment on Cu-rich and Cu-poor CuInSe2, which show a different influence of interface recombination without the treatment. We develop a potassium postdeposition treatment that can be applied to Cu-rich material, where an additional etching step is necessary. The same postdeposition treatment with etching step is applied to Cu-poor material. In both cases we observe an increase of the power conversion efficiency and open circuit voltage. Comparing the increase in open circuit voltage to the increase in quasi-Fermi level splitting indicates that the improvement in Cu-poor solar cells is mostly due to changes in the bulk, whereas in Cu-rich solar cells both the bulk and the interface are improved. The improvement of the interface is corroborated by temperature dependent current-voltage characteristics, which show that the dominating recombination path in Cu-rich solar cells moves from the interface to the bulk after treatment and by admittance spectroscopy, which shows that the treatment removes a 200 meV deep defect. Photoluminescence spectroscopy shows that even in Cu-rich material the alkali treatment creates a Cu-poor surface, which in this case cannot be created by diffusion of Cu into the bulk, but is grown during the treatment.

Thin film tandem solar cells provide a promising approach to achieve high efficiencies. These tandem cells require at least a bottom low bandgap and an upper high bandgap solar cell. In this contribution, 2 high-performance Cu(In,Ga)Se2 cells with bandgaps as low as 1.04 and 1.07 eV are presented. These cells have shown certified efficiencies of 15.7% and 16.6% respectively. Measuring these cells under a 780-nm longpass filter, corresponding to the bandgap of a typical top cell in tandem applications (1.57 eV), they achieved efficiencies of 7.9% and 8.3%. Admittance measurements showed no recombination active deep defects. One additional high-performance CuInSe2 thin film solar cell with bandgap of 0.95 eV and efficiency of 14.1% is presented. All 3 cells have the potential to be integrated as bottom low bandgap cells in thin film tandem applications achieving efficiencies around 24% stacked with an efficient high bandgap top cell.

Low temperature post-deposition treatment of Cu2ZnSnSe4 with NaF and KF significantly improved the solar cell efficiency (from 6.4% to 7.8% and 7.7% on average, respectively) due to enhanced fill factor (from 0.58 to 0.61 and 0.62), open-circuit voltage (Voc) (from 314 mV to 337 mV and 325 mV) and short-circuit current density (from 35.3 mA⋅cm −2 to 38.3 mA⋅cm −2 and 38.6 mA⋅cm −2). Voc improvement was higher for solar cells with NaF treatment due to an increase in radiative efficiency at room temperature and shallower defect activation energy as determined by photoluminescence (PL) and temperature dependent admittance spectroscopy, respectively. In the case of KF treatment, red-shift of the PL, higher band tail density of state and donor activation energy deeper in the band gap were limiting further improvement of the Voc compared to NaF treatment.

In this paper, we show that CuInSe2 (CIS) absorbers grown under Cu-excess have better collection efficiencies compared to Cu-poor ones. We also show that an ex situ potassium fluoride postdeposition treatment leads to an improvement in VOC for CIS absorbers grown under both Cu-excess and Cu-poor conditions. Additionally, for absorbers grown under Cu-excess, the junction breakdown, which is observed in reverse bias of untreated cells, is removed. This improvement is based mainly on improving the interface of the CIS absorber grown under Cu-excess to the cadmium sulphide buffer layer through moving the dominant recombination from the interface to the bulk. In contrast to observations in the literature, the treated surface is not completely Cu-free.

We investigate the dopant concentration and majority carrier mobility in epitaxial CuInSe2 thin films for different copper-to-indium ratios and selenium excess during growth. We find that all copper-poor samples are n-type, and that hopping conduction in a shallow donor state plays a significant role for carrier transport. Annealing in sodium ambient enhances gallium in-diffusion from the substrate wafer and changes the net doping of the previously n-type samples to p-type. We suggest that sodium incorporation from the glass might be responsible for the observed p-type doping in polycrystalline Cu-poor CuInSe2 solar cell absorbers. [ABSTRACT FROM AUTHOR]

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The use of new technologies has determined the development and spread of new models of shared knowledge, enhancing artistic and cultural heritage: in particular, through cloud and IoT systems, cultural assets take on the characteristics of smart cultural objects, becoming modalities of easier diffusion and wider sharing of knowledge. In parallel, the multiplication of online communication methods has enhanced new and more dynamic ways of knowledge sharing, in particular regarding the “experiential knowledge”, which brings together documentary knowledge and a more personal, interpretative character. In this way, we can consider the phenomenon of so-called "semantic heritage community generated data", which, through a series of services (i.e. tagging, QR Code tags and RFID) allow the acquisition and sharing of experiences and contents related to objects of art or monuments and buildings. The generated data flow collects personal data and non-personal data and therefore requires the adoption of protective measures in compliance with 679/2016 / EU (GDPR) and Regulation 1087/2018 / EU (free flow of non-personal data in the EU), to guarantee rights regarding both people and properties. The proposed paper analyses some legal aspects of "semantic heritage community generated data", with attention to (personal and non-personal) data protection and the possibilities of use/processing by public bodies and private companies. Cultural Heritage UGC e tutela dei dati personali L’utilizzo delle nuove tecnologie ha reso possibile l’elaborazione e la diffusione di nuovi modelli di conoscenza condivisa per valorizzare il patrimonio artistico e culturale: in particolare, attraverso sistemi cloud ed IoT, i beni culturali assumono le caratteristiche di smart cultural object, divenendo veicoli di facile diffusione e più ampia condivisione della conoscenza. In parallelo, la moltiplicazione dei canali di comunicazione ha valorizzato nuove e più dinamiche forme di condivisione della conoscenza, in particolare con riferimento alla conoscenza esperienziale, che si affianca alla conoscenza documentale con un carattere più personale ed interpretativo; vengono così in considerazione i cosiddetti semantic heritage community generated data, che, attraverso una serie di servizi (es. tagging, tag QR Code e RFID) permettono acquisizione e condivisione di esperienze e contenuti collegati ad oggetti d’arte o a monumenti ed edifici. Il flusso di dati così generato raccoglie dati personali e dati non personali e richiede, pertanto, la predisposizione di misure di tutela nel rispetto dei Regolamenti 679/2016/Ue (GDPR) e 1087/2018/Ue (free flow of non-personal data in the EU), per garantire le situazioni giuridiche, personali e proprietarie. Il paper proposto analizza i profili giuridici dei semantic heritage community generated data, con particolare riferimento alla tutela dei dati ed alle possibilità di utilizzo/trattamento da parte di soggetti pubblici e privati.