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The temperature-dependent evolution of the photoluminescence (PL) properties of a highly emissive Cs2Ag0.35Na0.65Bi0.02In0.98Cl6 perovskite was examined in the range of 80–340 K. The PL maximum exhibited a shift to higher energies with an increase in T, while the bandgap decreased with elevated T. This behavior can be explained by a thermal distribution of the self-trapped exciton states.

A new single-step and green approach for the synthesis of microcrystalline Cs2AgxNa1−xBiyIn1−yCl6 (CANBIC) perovskites in ambient conditions is introduced. The CANBIC powders emit broadband self-trapped excitonic photoluminescence (PL) with a champion PL quantum yield (QY) of 98 ± 2% and a PL lifetime of ca. 2 μs observed for x = 0.40 and y = 0.01–0.02. The study focuses on the dependence of structural, spectral, and photophysical properties of CANBICs on Bi content. CANBICs are solid solutions with isomorphous In-to-Bi substitution with the bandgap and valence band edge energy decreasing gradually with increasing y. The PL QY and the rate constant of the radiative recombination showed volcano-shaped dependences on the Bi content, while the rate of the non-radiative recombination revealed a drastic growth by three orders of magnitude as the Bi fraction y was elevated from 0.01 to 1.0 indicating that BiCl6 units are responsible for non-radiative recombination.

Maßgeschneiderte Modifizierungen bleifreier Halogenid-Perowskite (BHP) durch Dotierung/Legierung mit Metallkationen gelten als vielversprechender Weg zu hocheffizienten anorganischen Leuchtstoffen mit Photolumineszenz (PL)-Quantenausbeuten von bis zu 100 %. Solche Materialien weisen typischerweise eine selektive Empfindlichkeit gegen UV-Licht, einen breiten PL-Bereich, lange PL-Lebensdauern und eine einzigartige Variabilität und Stabilität der Zusammensetzung auf – eine ideale Kombination für viele Lichtsammelanwendungen. Dieser Kurzaufsatz stellt den Stand der Technik bei dotierten BHPs vor, mit dem Schwerpunkt auf Berichten aus den letzten 2–3 Jahren. Wir diskutieren die Faktoren, die die Effizienz und die spektralen Parameter der Breitband-PL von dotierten BHP abhängig von Dotierstoff und Wirtsmatrix im mikro- wie auch im nanokristallinen Zustand bestimmen, gehen auf die wichtigsten Herausforderungen in diesem sich rasch entwickelnden Forschungsbereich ein und skizzieren die vielversprechendsten Konzepte, um weitere Fortschritte in diesem Bereich zu erzielen.

Doping with In(iii) induces the formation of stable and phase-pure Cs2AgxNa1−xFeyIn1−yCl6 perovskites with bandgaps close to 2 eV.

Thermal deposition of halide perovskites as a universal and scalable route to transparent thin films becomes highly challenging in the case of lead-free double perovskites, requiring the evaporation dynamics of multiple metal halide sources to be balanced or a single-phase precursor preliminary synthesized to achieve a reliable control over the composition and the phase of the final films. In the present Letter, the feasibility of the single-source vacuum deposition of microcrystalline Cs2AgxNa1-xBiyIn1-yCl6 double perovskites into corresponding transparent nanocrystalline films while preserving the bulk spectral and structural properties is shown. The perovskite films produced from the most emissive powders with x = 0.40 and y = 0.01 revealed a photoluminescence quantum yield of 85%, highlighting thermal evaporation as a promising approach to functional perovskite-based optical materials.

Tailored modifications of halide lead‐free perovskites (LFPs) via doping/alloying with metal cations have been recognized as a promising pathway to highly efficient inorganic phosphors with photoluminescence (PL) quantum yields of up to 100 %. Such materials typically display selective sensitivity to UV light, a broad PL range, and long PL lifetimes as well as a unique compositional variability and stability—an ideal combination for many light‐harvesting applications. This Minireview presents the state‐of‐the‐art in doped LFPs, focusing on the reports published mostly in the last two to three years. We discuss the factors determining the efficiency and spectral parameters of the broadband PL of doped LFPs depending on the dopant and host matrix, both in micro‐ and nanocrystalline states, address the most relevant challenges this rapidly developing research area is facing, and outline the most promising concepts for further progress in this field.

Feasibility of the identification of backsheet (BS) composition of field-aged Si photovoltaic (PV) modules based on the analysis of characteristic patterns of UV-excited fluorescence (UVF) of ethylene vinyl acetate copolymer encapsulant is shown. The approach includes BS identification by vibrational spectroscopies and the formation of a database of BS-related characteristic UVF patterns. A multivariate principal component analysis of the UVF images of unknown samples combined with the UVF pattern database allows the BS type to be identified only from UVF images. The geometric place of particular samples in the principal component plots is indicative of the general degradation status of PV modules. The proposed method can be applied for high-throughput noncontact characterization of solar PV plants.

Degradation of backsheets (BSs) of commercial silicon PV modules is currently recognized as a source of reduced module performance and module failure. Monitoring of the BS state in the field is possible by using non-destructive and highly informative near-infrared absorption (NIRA) spectroscopy. Application of NIRA for the analysis of multi-layer polyethylene terephtalate (PET) based BSs, which dominate the PV module market, is challenging due to a large variety of possible BS configurations that show only small differences in NIRA spectra. In the present work, a spectroscopic tool for the structural identification of PET-based BSs is introduced. The method is based on a principal component analysis of a database of 250 representative NIRA spectra of BSs of different types. It allows a BS with an unknown structure to be assigned to one of 12 different types based solely on its NIRA spectrum. The identification was successfully validated on a test collection of 45 selected BSs and shown to be feasible for the field deployment. Further automation of NIRA measurements and spectral analysis are expected to elevate the proposed tool to the level of a non-intrusive high-throughput field analysis of the BS composition and state in operating PV module grids.

We introduce a new concept of a “bottom-to-top” design of intercalate carbon nitride compounds based on the effects ofself-assembly of colloidal single-layer carbon nitride (SLCN) sheets stabilized by tetraethylammonium hydroxide NEt4OHupon ambient drying of the water solvent. These effects include (i) formation of stage-1 intercalates of NEt4OH during theambient drying of SLCN colloids on glass substrates and (ii) the spontaneous formation of layered hexagonally-shapednetworks of SLCN sheets on freshly-cleaved mica surfaces. The dynamics of the intercalate formation was followed by in situX-ray diffraction allowing different stages to be identified, including the deposition of a primary “wet” intercalate of hydratedNEt4OH and the gradual elimination of excessive water during its ambient drying. The intercalated NEt4+ cations show aspecific “flattened” conformation allowing the dynamics of formation and structure of the intercalate to be probed byvibrational spectroscopies. The two-dimensional self-assembly on mica is assumed to be driven both by the internalhexagonal symmetry of heptazine units and by a templating effect of the mica surface.

Cutting-edge research on graphite-like carbon nitride-based (g-C3N4) photocatalytic systems for molecular nitrogen fixation is summarized. The properties of modified g-C3N4 with grafted functional groups, structural defects (nitrogen or carbon vacancies), doped with nonmetals and metals, as well as g-C3N4-based binary and ternary composites with the participation of metals, their oxides, metalates, carbonates, hydrocarbons, and sulfides are discussed. The most promising areas of further research are outlined.

The cutting-edge research on the photocatalytic selective reductive transformations of organic nitro compounds in heterogeneous systems on the basis of semiconductors of different nature, composites based on them, plasmonic photocatalysts, and other materials is considered. The reactions leading to amines, azo and azoxy compounds, imines, products of N-alkylation, N-formylation, as well as cyclization of quinolines, hydroquinolines, benzimidazoles, and indazoles, are analyzed. Possible ways of further research of selective photocatalysis are outlined.

This Perspective provides a critical summary of the current state of the art in the synthesis and properties of polyheptazine single-layer carbon nitride (SLCN). The summary combines the authors' research and literature reports on SLCN concerning the synthesis of single-layer polyheptazine sheets, light absorption and emission by SLCN, photochemical and photocatalytic properties of SLCN as well as examples of applications of SLCN sheets as "building blocks" in heterostructures with nanocrystalline semiconductors and metals. The Perspective is concluded with an outlook discussing the most promising directions for further studies and applications of SLCN and related composites.

A mild aqueous synthesis of colloidal 2-4 nm (Cu,Ag)-In-S (CAIS) quantum dots (QDs) stabilized by surface metal complexes with glutathione was introduced. Linear variations of the interplanar distances as well as of the characteristic Ag(Cu)-S-related Raman vibrational frequencies of CAIS QDs with increasing copper content show such QDs to be solid solutions rather than a mixture of AIS and CIS phases. At the same time, the band gaps and the energies of photoluminescence (PL) band maxima of CAIS QDs show non-monotonous changes decreasing from AIS to CAIS QDs (50 molar% Cu) and then increasing back for Cu-richer CAIS compositions and pure CIS. This behavior was interpreted as a result of the band bowing phenomenon. The bowing parameters of CAIS QDs determined from both absorption spectra (1.10 eV) and PL spectra (0.38 eV) are close to the range typically reported for ternary bulk MI-MIII-S compounds with the MI sites occupied by a mixture of copper and silver cations. The PL intensity of CAIS QDs was found to decrease during PL registration due to the photochemical decomposition of QDs, the efficiency of this process increasing with increasing copper content. A similar trend was found in the photocatalytic reduction of methylviologen cations by hydrosulfide anions in the presence of CAIS. The initial rate of this reaction increased monotonously from AIS to CAIS to CIS QDs, with the activity of the CAIS QDs (50 molar% Cu) and pure CIS QDs being respectively 1.5 and 2.7 times higher than the photoactivity of pure AIS QDs. This trend is compliant with a strong decrease in the PL emission efficiency observed from AIS to CAIS to CIS QDs. Similar optical and photochemical properties were revealed for core/shell CAIS/ZnS QDs. The band-bowing effect and photochemical activity of mixed CAIS (CAIS/ZnS) QDs open good perspectives for light-conversion applications in the photon energy range down to 1.8 eV.

We provide a critical review of the current state of the synthesis and applications of nano- and micro-tubes of layered graphitic carbon nitride. This emerging material has a huge potential for light-harvesting applications, including light sensing, artificial photosynthesis, selective photocatalysis, hydrogen storage, light-induced motion, membrane technologies, and can become a major competitor for such established materials as carbon and titania dioxide nanotubes. Graphitic carbon nitride tubes (GCNTs) combine visible-light sensitivity, high charge carrier mobility, and exceptional chemical/photochemical stability, imparting this material with unrivaled photocatalytic activities in photosynthetic processes, such as water splitting and carbon dioxide reduction. The unique geometric GCNT structure and versatility of possible chemical modifications allow new photocatalytic applications of GCNTs to be envisaged including selective photocatalysts of multi-electron processes as well as light-induced and light-directed motion of GCNT-based microswimmers. Closely-packed arrays of aligned GCNTs show great promise as multifunctional membrane materials for the light energy conversion and storage, light-driven pumping of liquids, selective adsorption, and electrochemical applications. These emerging applications require synthetic routes to GCNTs with highly controlled morphological parameters and composition to be available. We recognize three major strategies for the GCNT synthesis including templating, supramolecular assembling of precursors, and scrolling of nano-/microsheets, and outline promising routes for further progress of these approaches in the light of the most important emerging applications of GCNTs.

Reliable and durable solar power plants require PV modules with high-grade polymer encapsulants and backsheets (BSs). For performance analyses of PV installations fast, reliable and non-destructive methods for determining composition and degradation state of polymer components need to be developed. Here, we show that the structure of some common polymer BSs can be determined in the field in real time by analyzing near-infrared transmission (NIRT) spectra collected under illumination with natural sunlight. The potential of this “Solar-NIRT” method was probed by field measurements on a multi-MW PV power plant where four major BS types were identified by multispectral cross-sectional Raman imaging. Additionally, degradation of a particular BS type was found to result in distinct changes in NIRT spectra allowing the degraded BSs to be classified as a separate type. Principal component analysis (PCA) applied to a collection of 62 Solar-NIRT spectra allowed to create a map of five clusters, each corresponding to a particular BS type. The feasibility of using the PCA cluster map for the identification of unknown samples was shown on a test set of 13 different BSs. The Solar-NIRT is relatively fast, non-invasive, selective, can be upgraded to a non-contact regime making it a promising tool for high-throughput characterization.

A new “green” and mild synthesis of highly stable microcrystalline Cs2AgxNa1−xBiyIn1−yCl6 (CANBIC) perovskites under ambient conditions was developed that is scalable to the multi-gram production. Under UV illumination, the CANBIC perovskites emit intense broadband photoluminescence (PL) with a quantum yield (QY) of 92% observed for x = 0.35 and y = 0.01–0.02. The combination of strong UV absorbance and broadband visible emission, high PL QY, and long PL lifetimes of up to 1.4 μs, along with an outstanding stability makes these CANBICs a promising material class for many optical applications.Graphical abstract: “Green” synthesis of highly luminescent lead-free Cs2AgxNa1−xBiyIn1−yCl6 perovskitesLead halide perovskites have gone through an unprecedented rapid development from one of many promising photovoltaic materials to a real competitor for established photovoltaic absorbers such as silicon, copper–indium–gallium chalcogenides, and CdTe.1–4 This triggered the search for novel lead-based perovskite compounds and particularly for “greener” lead-free structural analogs with comparable optical and photovoltaic characteristics. Due to the many possible compositions of lead-free perovskites (LFPs), especially of the so-called double LFPs with a couple of Pb2+ being substituted by M+M3+ combinations,1,3 there are hundreds of structures which could be identified as promising candidates for photovoltaics, light emission, and light management (down-shifting, up-conversion, etc.).1,3–6 Given the broad variability of alkali metal and halide positions in LFPs, these structures translate into thousands of compounds to be synthesized and tested for light-conversion applications which presents a huge experimental challenge.LFP tunability can be exemplified by In-based double compounds, A2MIInX6 (A – alkali metals, X – halides), where all four positions can be independently varied. In particular, MI can be occupied by Na+, K+, Ag+ or their mixtures, A – by Cs+, Rb+, or organic cations, and X – by individual and mixed halides. At the same time, InIII can be substituted by a number of MIII cations, including BiIII and SbIII.1,4 The interest in such compounds, particularly in Bi-doped Cs2AgxNa1−xInCl6 (referred to as CANIC) or Cs2AgxNa1−xBiyIn1−yCl6 (referred to as CANBIC), is constantly growing due to their intense broadband photoluminescence (PL) combined with a unique tunability of the photophysical properties and an outstanding chemical stability.5–21In view of this compositional variability, the progress in the material science of LFP requires a transition from conventional single-compound trials to high-throughput studies based on robot-assisted synthesis and characterization, ideally supported by machine-learning-based data analysis.22–24 The feasibility and efficiency of high-throughput experiments in the field of lead perovskite photovoltaics were recently demonstrated.25–30However, the majority of the reported syntheses of double LFPs require high energy input by hydrothermal treatment or calcination. Furthermore, a considerable amount of manual intermediate steps is needed which cannot be automated, as well as the usage of hazardous chemicals such as concentrated HCl in the case of chloride LFPs1,3,6,7,9,14,17,21 or unstable and aggressive substances for bromide and iodide LFPs.1,3,21 More favorable milder temperature-, saturation-, or antisolvent-driven precipitation approaches, conventionally employed for the fabrication of lead-based perovskites, often yield poorly controlled mixtures of perovskite and non-perovskite phases when applied to double LFPs.1,13,31 As a result, the development of simple and mild procedures for the reproducible and phase-controlled synthesis of double LFPs under ambient conditions with robotized equipment still remains challenging.In this communication, we introduce such an approach to the fabrication of microcrystalline lead-free CANIC and CANBIC perovskites, yielding compositionally controlled single-phase products under ambient conditions in a single step without any additional thermally activated steps or the need for hazardous chemicals. By focusing on the optical properties of the most strongly emissive CANBIC perovskite composition, we show that our approach results in a very stable and structurally perfect material emitting broadband PL in the visible spectral range with a PL quantum yield (QY) close to unity.

Over the last years, a significant number of inverter shutdowns most likely due to degraded backsheets have been reported by operators, investors, and manufacturers. We investigated water ingress into different backsheets, and the resulting risk for inverter shutdowns. For studying pending insulation issues of inverters, we analyzed exemplarily a 5-MWp photovoltaic (PV) power station with 20,530 PV modules and 314 inverters. For backsheet identification on-site near-infrared absorption spectroscopic measurements of 518 PV modules from 20 inverters were carried out. In the lab, wet leakage tests provide kinetic data of insulation resistances for different backsheet materials. Historic ground impedance data logged by the inverter were evaluated to show the temporal evolution of inverters with different backsheets. We observe different kinetics and drops in leakage resistance for different backsheet types based on polyamide (PA) and air-side fluorinated coating (FC), and distinguish between two types of behavior. “PA-like” is characterized by moderate leakage resistance loss and slower performance reduction with regard to insulation in the field. “FC-like” is characterized by high susceptibility to water and a high leakage resistance loss rate for PV modules after 6–8 years of operation. These characteristics are indicated when measuring inverter GI in dependence of temperature and humidity. For PA-based BSs, the reduction in ground impedance (GI) is steady over 8 years. We observe incidences with GI below the critical value of 400 kΩ on 2.8% of all days. For FC-based BSs, we also observe steady decrease of average GI initially, yet after 6 years in the field, we see a sudden and rapid decline for 20% of those inverters. GI falling below the critical value is observed on up to 5% of all days, with the trend increasing. Therefore we, expect this problem to become even more severe for longer operating times.

Polymers are essential for long-term green energy production by photovoltaics (PV). We created a unique dataset that links electrical performance data of 28,030 PV modules, combined into 1295 strings and 423 inverters with the identity of the backsheet (BS) materials of each of the tested modules. This dataset gives an insight into BS-versatility and resulting impact on the insulation resistance of strings and inverters. The BSs were analyzed using near infrared absorption spectroscopy (NIRA) plus visual inspection in the field. The insulation resistance (Riso) of selected modules and strings was measured on-site. Furthermore, reported ground impedance (GI) values were evaluated with respect to an inverter-specific threshold below which the inverters do not start operation. We differentiated seven BS-types, the three most frequent being polyamide (PA), fluorinated coating (FC), and polyvinylidene fluoride (PVDF). Although modules with PA show often BS cracking, the insulation resistance was above the threshold. Similar, the GI of inverters with modules with PVDF-BSs was high. Modules with FC-BSs feature generally low Riso–values on module-, string-, and on inverter level. Evaluating historic data reveals an increase in frequency of GI-values below the threshold for inverters connected to modules with exclusively FC-BSs. While inverters with modules having PA- or PVDF-BSs function as expected, inverters with modules having FC-BSs require maintenance to keep power yield on an acceptable level. The dataset collected in the present work highlights that the choice of BS-material of PV-modules is essential for reliable operation of PV power stations.

For large-scale fabrication of optical circuits, tailored subwavelength structures are required to modulate the refractive index. Here, we introduce a colloid-to-film-coupled nanocavity whose refra...

We present a technique for the simultaneous photostructuring of hydrogels on the μm scale with different compositions on one substrate. The existing methods (e.g. spin-coating of the hydrogel precursor and application of simple moulds or spacers) have less potential to integrate spatially separated functional hydrogel dots as needed for the fabrication of complex polydimethylsiloxane (PDMS) on-glass microfluidic chips. Here, we report a method for the fast production of precisely placed hydrogel structures with adjustable height (≤80 μm) and width (≤500 μm) on glass substrates utilizing black polyoxymethylene moulds. The integration of several chambers for different hydrogel precursor solutions in one mould allows the simultaneous photopolymerization of hydrogels with different compositions. To visualize the difference in composition of the hydrogel dots and to demonstrate the precision in structuring, various quantum dots were added to the hydrogel precursor solutions and physically entrapped during the photopolymerization. To show the high potential of our photostructuring method, a microfluidic double-chamber reactor was designed and the variability in the performance of tri-enzymatic cascade reactions with optionally spatially separated or non-separated enzymes β-galactosidase, glucose oxidase, and horseradish peroxidase was visualized.

The effect of flash-lamp annealing (FLA) on the re-crystallization of thin films made of colloidal Cu2ZnSnS4 nanocrystals (NCs) is investigated by Raman spectroscopy. Unlike similar previous studies of NCs synthesized at high temperatures in organic solvents, NCs in this work, which have diameters as small as 2–6 nm, were synthesized under environmentally friendly conditions in aqueous solution using small molecules as stabilizers. We establish the range of FLA conditions providing an efficient re-crystallization in the thin film of NCs, while preserving their kesterite structure and improving their crystallinity remarkably. The formation of secondary phases at higher FLA power densities, as well as the dependence of the formation on the film thickness are also investigated. Importantly, no inert atmosphere for the FLA treatment of the NCs is required, which makes this technology even more suitable for mass production, in particular for printed thin films on flexible substrates.

The synthesis of (Cu,Ag)-Zn-Sn-S (CAZTS) and Ag-Zn-Sn-S (AZTS) nanocrystals (NCs) by means of “green” chemistry in aqueous solution and their detailed characterization by Raman spectroscopy and several complementary techniques are reported. Through a systematic variation of the nominal composition and quantification of the constituent elements in CAZTS and AZTS NCs by X-ray photoemission spectroscopy (XPS), we identified the vibrational Raman and IR fingerprints of both the main AZTS phase and secondary phases of Ag-Zn-S and Ag-Sn-S compounds. The formation of the secondary phases of Ag-S and Ag-Zn-S cannot be avoided entirely for this type of synthesis. The Ag-Zn-S phase, having its bandgap in near infrared range, is the reason for the non-monotonous dependence of the absorption edge of CAZTS NCs on the Ag content, with a trend to redshift even below the bandgaps of bulk AZTS and CZTS. The work function, electron affinity, and ionization potential of the AZTS NCs are derived using photoelectron spectroscopy measurements.

In this work we introduce a combination of spectral, imaging and electric lab and field tests that complement field I-V and power measurements and allow to track the insulation failures of the solar modules and associate various failure modes with different types of the module backsheets.

The variation of the cationic composition in I2-II-IV-VI4 semiconductor compounds is an effective tool for altering their properties in a controlled manner. In particular, a partial substitution of Cu for Ag in kesterite Cu2ZnSnS4 was proposed to suppress Cu-Zn antisite defects and the improve photovoltaic performance. However, the efficiency of this approach may substantially depend on the fabrication route. Here, we report on the synthesis of (Cu,Ag)-Zn-Sn-S (CAZTS) and Ag-Zn-Sn-S (AZTS) nanocrystals (NCs) by means of "green" chemistry in aqueous solution and their detailed characterization by Raman spectroscopy and by several complementary techniques. Through a systematic variation of the nominal composition and quantification of the constituent elements in CAZTS and AZTS NCs by XPS, we identified the vibrational Raman and IR fingerprints of both the main AZTS phase and secondary phases of Ag-Zn-S and Ag-Sn-S compounds (for the first time). The formation of the secondary phases of Ag-S and Ag-Zn-S cannot be avoided entirely for this type of synthesis. The Ag-Zn-S phase, having its bandgap in near infrared range, is the reason of the non-monotonous dependence of the absorption edge of CAZTS NCs on the Ag content, with a trend to redshift even below the bandgaps of bulk AZTS and CZTS.

We report on electron paramagnetic resonance (EPR) spectroscopy of Cu-Zn-Sn-S nanocrystals (NCs) synthesized by a colloidal chemistry method. The chemical composition of the NCs is characterised by a strong deficit of tin and slight zinc enrichment with respect to the "ideal" stoichiometry of kesterite Cu2ZnSnS4. Nevertheless, X-ray photoemission spectroscopy (XPS) shows that the net cation/anion ratio is very close to 1:1 and the valences states of the constituents correspond to those of Cu2ZnSnS4, in particular Cu+. The kesterite crystal structure of the NCs is confirmed by X-ray diffraction and Raman spectroscopy. Observing the EPR features for such CZTS NCs characteristic of individual Cu2+ embedded in the crystal lattice can be directly related with cationic disorder and non-stoichiometry. In particular, as a result of Cu-Zn antisites, Sn deficiency, and likely multivalence, a very small fraction of copper ions may occur in the Cu2+ state. The concentration of Cu2+ sites of ~1017-1018 cm-3 assessed from the EPR spectra is below the sensitivity of XPS, therefore the latter is dominated by the prevailing Cu+ species. The temperature dependence of the I-V curves reveal a level at about 0.2 eV above the valence band that can be assigned to the CuZn antisite (with copper presumably in Cu2+ state) and a 14 meV level above valence band that can correspond to VCu. The new insights reported here into the relation between the structure and electronic states of CZTS NCs are important for advancing their applications.

The effect of spontaneous alloying of non-stoichiometric aqueous Ag-In-S (AIS) and Cu-In-S (CIS) quantum dots (QDs) stabilized by surface glutathione (GSH) complexes was observed spectroscopically due to the phenomenon of band bowing typical for the solid-solution Cu(Ag)-In-S (CAIS) QDs. The alloying was found to occur even at room temperature and can be accelerated by a thermal treatment of colloidal mixtures at around 90 °C with no appreciable differences in the average size observed between alloyed and original individual QDs. An equilibrium between QDs and molecular and clustered metal-GSH complexes, which can serve as "building material" for the new mixed CAIS QDs, during the spontaneous alloying is assumed to be responsible for this behavior of GSH-capped ternary QDs. The alloying effect is expected to be of a general character for different In-based ternary chalcogenides.

This study links chemical analysis of PV-module’s backsheet components with the power output of PV-systems during their lifetime. Several PV-systems all with two or more module types and also backsheet types were investigated. We identified three classes of backsheet types with respect to their influence on the module performance. While PV-modules with robust backsheets (e.g. double-fluoropolymers) perform constantly well over years, others show linear or even exponential performance losses, while others display total failure (e.g. single-fluoropolymers or non-fluoropolymers). Humidity is a most probable driving factor for the faster ageing process of modules with critical backsheets in terms of their chemical layer components and the resulting properties.

We present a detailed analysis of Raman and infrared (IR) phonon spectra of strongly luminescent non-stoichiometric M-In-S (M = Cu, Ag, Hg) and core/shell M-In-S/ZnS nanocrystals (NCs) of small size (d 2-4 nm), formed by means of aqueous colloidal chemistry under mild conditions. Despite presumably similar factors determining position and broadening of the Raman and X-ray diffraction (XRD) peaks, phonon spectra are shown to be more sensitive to NC composition and crystals structure. The spectral Raman pattern of these strongly M-deficient M-In-S NCs is different from that of the corresponding stoichiometric phases, e.g. CuInS2 or AgIn5S8, and excludes its assignment to relevant binary sulfides, e.g. In2S3. Resonant behavior of relative peak intensities in Raman spectra is different from that of larger-size stoichiometric NCs and bulk samples studied before, while the temperature dependence reveals an analogous enhancement of the highest-frequency LO modes supporting an unambiguous assignment of the latter. Therefore, we conclude that the Raman spectra observed are characteristic of the specific structure of these highly non-stoichiometric small NCs. IR modes of these NCs occur in the same frequency range as the Raman ones but at higher frequencies than the IR phonons in bulk material. The IR spectra are less characteristic, compared to Raman ones, revealing more similarity among the three NC compounds and with the bulk counterparts.

The aim of this study is to establish reliable spectroscopic fingerprints of compounds that may form as secondary phases in Cu2ZnSnS4 (CZTS) nanocrystals (NCs) synthesized by “green” colloidal chemistry directly in aqueous solutions or during post-processing of NC films for photovoltaic application. For this purpose, we investigated a series of binary and ternary compound NCs synthesized under the same conditions as the quaternary CZTS NCs. The capabilities of combined Raman and X-ray photoemission (XPS) spectroscopies are used to identify these compounds formed separately and define spectral fingerprints for distinguishing them as possible secondary phases in the spectra of CZTS NCs. Besides the conventional analysis of element ratios and chemical shifts of the core-level peaks in the XPS spectra, the careful analysis of Auger lines and modified Auger parameters are applied to distinguish otherwise similar spectral contributions of different compounds. In the case of CuxS NCs the binding energy separation between the Cu2p3/2 and S2p3/2 core-levels is used as the additional fingerprint. As a criterion of a certain crystal structure in Raman spectroscopy, we rely not only on frequency positions of particular phonon modes but also on selective probing of different compounds at different (resonant) excitation wavelengths. The reasons of controversial previous reports on Raman spectra of CuxS are revealed and characteristic Raman spectra of Sn-poor Cu-Sn-S and Sn-poor Zn-Sn-S are proposed. For Cu-Zn-S, a mixture of CuxS and ZnS is formed under the given mild conditions rather than ternary compounds or alloys.

Ternary metal-chalcogenide quantum dots (QDs), including copper and silver-indium-sulfide QDs and related core/shell QDs, combine broad tunability of optical properties through extensive variations in the QD composition and size with a unique photoluminescence (PL) emission behavior. In particular, the PL of nonstoichiometric Ag-In-S (AIS) QDs and core/shell AIS/ZnS QDs reveals a combination of properties typical for excitonic emission (high quantum yields, distinct size dependence of spectral PL parameters, characteristic temperature dependences) while simultaneously revealing a large spectral width of emission bands typically observed for defect-related radiative recombination. In this view, the origins and mechanisms of the broadband PL of such ternary QDs remain a topic of vivid discussions.

We introduce a direct aqueous synthesis of luminescent 2-3 nm Ag-In-Se (AISe) quantum dots (QDs) capped by glutathione (GSH) complexes, where sodium selenosulfate Na2SeSO3 is used as a stable Se2- precursor. A series of size-selected AISe QDs with distinctly different positions of absorption and PL bands can be separated from the original QD ensembles by using anti-solvent-induced size-selective precipitation. The AISe-GSH QDs emit broadband PL with the band maximum varying from 1.65 eV (750 nm) to 1.90 eV (650 nm) depending on the average QD size and composition. The PL quantum yield varies strongly with basic synthesis parameters (ratios of constituents, Zn addition, duration of thermal treatment, etc.) reaching 4% for “core” AISe and 12% for “core/shell” AISe/ZnS QDs. The shape and position of PL bands is interpreted in terms of the model of radiative recombination of a self-trapped exciton. The AISe-GSH QDs reveal phonon Raman spectra characteristic for small and Ag-deficient tetragonal Ag-In-Se QDs. The ability of ultra-small AISe QDs to support such "bulk-like" vibrations can be used for future deeper insights into structural and optical properties of this relatively new sort of QDs.

A new synthetic route to water-soluble ultra-small CdSe quantum dots (QDs) is proposed based on using a mixed complex of Cd(II) with ammonia and mercaptoacetate (MA) anions as a stabilizer and Na 3 SeO 3 as a stable and non-volatile selenium precursor that can be reduced in situ to Se 2− by MA. The method is facile, reproducible and allows gram-scale production of CdSe QDs in the form of powders, uniform and smooth films and concentrated solutions with a CdSe content up to 20 m%. At a molar MA/Cd(II) ratio of 2.25 the ultra-small CdSe QDs are characterized by an average size of around 2 nm and a narrow size distribution, as well as by a stability towards oxidation by ambient oxygen and under light illumination. A combined Raman and XPS study shows that the stability of the CdSe QDs arises from a thin layer of CdS on the QD surface formed during the post-synthesis thermal treatment. An increase in a MA/Cd(II) ratio to 4.00 results in the formation of a species that by its spectral characteristic resembles earlier reported “magic-size” (CdSe) 19 clusters. Upon heating this species transforms into CdSe QDs with a broadened size distribution.

Degradation of backsheets (BS) and encapsulant polymer components of silicon PV modules is recognized as one of the main reasons for losses in PV plant performance and lifetime expectations. Here, we report first insights into the correlation between BS composition of PV-modules and PV power station performance by using a combination of lab- and field-imaging, as well as spectroscopic and electrical characterizations. Using field-suitable near-infrared absorption (NIRA) spectroscopy, the BS structure of 518 PV-modules, 2.5 percent of the PV-modules in a 5 MWp PV power station, was identified on-site. The variance of the BS composition was found to be heterogeneous across PV-modules of the same power class from the same manufacturer. Polymaide-based BS cause in 10 out of 100 inverters ground impedance values below 400 kOhm, which is a typical threshold for inverters connecting to the grid. For primer-based BS this low value is reached 20 times. We conclude these numbers best as possible from the available monitoring data of inverters associated with BS-types from NIRA. Challenging is the identification of degraded primer-based BSs, since visually they look healthy and undistinguishable to well performing BSs. The present results demonstrate that a deeper understanding of the relationship between bill-of-materials and performance of PV-modules is necessary to avoid/minimize inverter shut-downs, and that it can be achieved by using combinations of selected field and lab characterization methods with monitoring data., 23 pages, 9 figures

The feasibility of a high-throughput robot-assisted synthesis of complex Cu1-xAgxInSySe1-x (CAISSe) quantum dots (QDs) by spontaneous alloying of aqueous glutathione-capped Ag–In–S, Cu–In–S, Ag–In–Se, and Cu–In–Se QDs is demonstrated. Both colloidal and thin-film core CAISSe and core/shell CAISSe/ZnS QDs are produced and studied by high-throughput semiautomated photoluminescence (PL) spectroscopy. The silver-copper-mixed QDs reveal clear evidence of a band bowing effect in the PL spectra and higher average PL lifetimes compared to the counterparts containing silver or copper only. The photophysical analysis of CAISSe and CAISSe/ZnS QDs indicates a composition-dependent character of the nonradiative recombination in QDs. The rate of this process is found to be lower for mixed copper-silver-based QDs compared to Cu- or Ag-only QDs. The combination of the band bowing effect and the suppressed nonradiative recombination of CAISSe QDs is beneficial for their applications in photovoltaics and photochemistry. The synergy of high-throughput robotic synthesis and a high-throughput characterization in this study is expected to grow into a self-learning synthetic platform for the production of metal chalcogenide QDs for light-harvesting, light-sensing, and light-emitting applications.

Results are summarized for studies of the spectral and luminescent properties of nonstoichiometric nanoparticles (NP) of Ag-In-S (AIS) and Cu-In-S (CIS) obtained in aqueous solutions. Using AIS NP stabilized by mercaptoacetate anions as an example, feasibility was demonstrated for size-selective precipitation for the separating out various sizes of nanoparticles from a colloidal ensemble of these particles, which display photoluminescence quantum yield up to 45%-46%. The prospects for further studies in this field and the development of potential applications of luminescent CIS and AIS in aqueous media are discussed.

The photoelectrochemical properties of FTO/TiO2/AIS nanoheterostructures containing Ag-In-S (AIS) nanoparticles (NPs) produced by the size-selective precipitation were investigated. It was found that the photocurrent of such composites increases by almost twice with decrease of the average AIS NP size from 3.5-4 to ~2 nm. The dependence of the rate constant of photoinduced electron transfer between AIS NPs and TiO2 on the average size of the NPs is similar in nature and agrees with the size dependence of the photoelectrochemical activity of TiO2/AIS nanoheterostructures.

A size-selected series of water-soluble luminescent Ag–In–S (AIS) and core/shell AIS/ZnS quantum dots (QDs) were produced by a precipitation technique. Up to 10–11 fractions of size-selected AIS (AIS/ZnS) QDs emitting in a broad color range from deep-red to bluish-green were isolated with the photoluminescence (PL) quantum yield reaching 47% for intermediate fractions. The size of the isolated AIS (AIS/ZnS) QDs varied from ∼2 to ∼3.5 nm at a roughly constant chemical composition of the particles throughout the fractions as shown by the X-ray photoelectron spectroscopy. The decrease of the mean AIS QD size in consecutive fractions was accompanied by an increase of the structural QD imperfection/disorder as deduced from a notable Urbach absorption “tail” below the fundamental absorption edge. The Urbach energy increased from 90–100 meV for the largest QDs up to 350 meV for the smallest QDs, indicating a broadening of the distribution of sub-bandgap states. Both the Urbach energy and the PL bandwidth of the ...

The introduction of single layer carbon nitride (SLCN) sheets into a colloidal ZnO solution in DMSO results in the termination of the growth of ZnO nanocrystals (NCs) and formation of binary colloidal ZnO/SLCN heterostructures with an average ZnO core size tunable between 3.0 and 5.5 nm. The ZnO/SLCN heterostructures reveal two photoluminescence (PL) bands corresponding to the ZnO core (a band peaked at 490–560 nm depending on the ZnO core size) and SLCN shell (a band peaked at 350 nm). The combination of SLCN and ZnO NCs into a heterostructure results in a reduction of the SLCN PL lifetime from 860 ns to 3.5–6.6 ns indicating the possibility of interfacial charge transfer from the photoexcited SLCN to the ZnO core NCs. At the same time, the of ZnO cores is also reduced from 0.70 to 1.49 μs for the core ZnO NCs with a “passive” SiO2 shell to 76–400 ns for the ZnO/SLCN heterostructures, indicating the possibility of photoinduced charge transfer from the ZnO core to the SLCN shell. The rate constant of such charge transfer was found to be 10.5 × 106–12.0 × 106 s−1 for the 3.0–3.6-nm ZnO cores and decreasing to 2.7 × 106 s−1 for 4.0-nm ZnO cores and to 1.1 × 106 s−1 for the 5.5-nm cores. The size dependence is caused by a decrease of the gap between a donor conduction band level of the ZnO cores and an acceptor conduction band level of the SLCN sheets. The ZnO/SLCN NCs also reveal a size-dependent capability of photoinduced charging under continuous UV excitation.

A treatment of graphitic carbon nitride (GCN) with concentrated nitric acid imparts GCN with the photocatalytic activity in hydrogen evolution from aqueous solutions of hydrazine hydrate, unsymmetric dimethylhydrazine (DMH) and hydrazinium sulfate under illumination with the UV light and in the presence of a Pd/SiO 2 co-catalyst. The rate of photocatalytic water reduction was found to be maximal in the presence of 3–5 M DMH and 12–14 M hydrazine hydrate and comparable to the hydrogen evolution rate in similar systems based on TiO 2 Evonik P25. The X-ray photoelectron spectroscopy of the activated GCN revealed that the acid treatment results in the elimination of some of the nitrogen atoms in the heptazine building blocks of the GCN and formation of carboxylic groups, the modification extent increasing with an increase of both duration of the acid treatment and the GCN synthesis temperature. The activation effect observed after the acid treatment of the GCN is assumed to originate from the participation of the introduced defects in the trapping and interfacial transfer of the photogenerated charge carriers. The maximal photoactivity was observed for the activated GCN produced at 500 °C followed by a 2-h contact with the concentrated HNO 3 .

Mesoporous hierarchical TiO 2 microspheres (MSs) with a size of 1–3 μm and an average pore size of 12.2–17.5 nm composed of smaller spherical 40–60-nm aggregates of discrete ∼10-nm anatase nanocrystals (NCs) were produced by the sol-gel transformation of Ti(IV) tetra butoxide in the presence of dibenzo-18-crown-6. Photocatalytic and photoelectrochemical properties of the TiO 2 MSs were studied in several processes important for the sustainable light-to-energy conversion and environmental photocatalysis. In particular, the TiO 2 MSs were found to be a much more efficient photocatalyst of the water reduction and the gas-phase oxidation of benzene and ethanol than irregularly aggregated mesoporous TiO 2 and a benchmark Evonik P25 TiO 2 . The MSs also revealed an advanced photoelectrochemical activity. The most probable reasons for the high photochemical activity of the MSs are (i) the effect of multiple scattering and reflection of light passing through the MSs that increases the probability of light absorption and (ii) the electron transport through the framework of interconnected loosely aggregated anatase NCs that results in suppression of the electron-hole recombination. In the photoelectrochemical cells based on the MS/CdS heterostructures the light is absorbed by a thin layer of the visible-light-sensitive CdS NCs and the advantages of the MSs are leveled off, the activity of TiO 2 as an electron transporting layer most probably limited by electrons leakage to the electrolyte.