Slot-die coating is a powerful method for upscaling the production of organic solar cells (OSCs) with low energy consumption print processes at ambient conditions. Herein, chlorobenzene (CB) and chloroform (CF) are compared as host solvents for printing films of the neat novel fused-ring unit based wide-bandgap donor polymer (PDTBT2T-FTBDT), the small molecule nonfullerene acceptor based on a fused ring with a benzothiadiazole core (BTP-4F) as well as the respective PDTBT2T-FTBDT:BTP-4F blend films at room temperature in air. Using CF printing of the PDTBT2T-FTBDT:BTP-4F active layer, OSCs with a high power conversion efficiency of up to 13.2% are reached in ambient conditions. In comparison to CB printed blend films, the active layer printed out of CF has a superior morphology, a smoother film surface and a more pronounced face-on orientation of the crystallites, which altogether result in an enhanced exciton dissociation, a superior charge transport, and suppressed nonradiative charge carrier recombination. Based on in situ studies of the slot-die coating process of PDTBT2T-FTBDT, BTP-4F, and PDTBT2T-FTBDT:BTP-4F films, the details of the film formation kinetics are clarified, which cause the superior behavior for CF compared to CB printing due to balancing the aggregation and crystallization of donor and acceptor.

Due to their intrinsically large surface-to-volume ratio, nanowires and nanofins interact strongly with their environment. We investigate the role of the main air constituents nitrogen, oxygen and water on the efficiency of radiative recombination in GaN nanostructures as a function of different surface treatments and at temperatures up to 200 °C. Oxygen and water exposures exhibit a complex behavior as they can both act quenching and enhancing on the photoluminescence intensity dependent on the temperature. For oxygen, these characteristics are already observed for low concentrations of below 0.5% in nitrogen. While the photoluminescence intensity changes induced by oxygen occur independently of illumination, the influence of water is light-induced: it evolves within tens of seconds under ultraviolet light exposure and is heavily influenced by the nanostructure pre-treatment. In contrast to observations in dry atmospheres, water prevents a recovery of the photoluminescence intensity in the dark. Combined measurements of the electrical current through GaN nanofins and their photoluminescence intensity reveal the environmental influence on the interaction of non-radiative recombination processes and changes in the surface band bending of the nanostructures. Several investigated solvents show an enhancing effect on the PL intensity increase, peaking in c-hexane with a 26-fold increase after 6 min of light exposure. Stabilization of the PL intensity was achieved by a passivation of the GaN surface with GaxOy, and ZnO shells. Surprisingly, Al2O3coatings resulted in a highly instable PL intensity during the first minutes of illumination. Our findings reveal the high importance of controlled environmental conditions for the investigation of nanostructures, especially when aimed at their applications in the fields of environmental sensing, photo-catalysis and light-emitting diodes.

Advanced MaterialsVolume 33, Issue 38 2170296 Inside Front CoverFree Access Surface-Anisotropic Janus Silicon Quantum Dots via Masking on 2D Silicon Nanosheets (Adv. Mater. 38/2021) Marc Julian Kloberg, Marc Julian Kloberg WACKER-Chair of Macromolecular Chemistry, Catalysis Research Center, Technical University of Munich, Lichtenbergstraße 4, 85758 Garching, GermanySearch for more papers by this authorHaoyang Yu, Haoyang Yu Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 CanadaSearch for more papers by this authorElisabeth Groß, Elisabeth Groß WACKER-Chair of Macromolecular Chemistry, Catalysis Research Center, Technical University of Munich, Lichtenbergstraße 4, 85758 Garching, GermanySearch for more papers by this authorFelix Eckmann, Felix Eckmann Chair of Experimental Semiconductor Physics II, Walter Schottky Institute and Physics Department, Technical University of Munich, Am Coulombwall 4, 85748 Garching, GermanySearch for more papers by this authorTassilo M. F. Restle, Tassilo M. F. Restle Chair for Inorganic Chemistry with Focus on New Materials, Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, D-85747 Garching, GermanySearch for more papers by this authorThomas F. Fässler, Thomas F. Fässler Chair for Inorganic Chemistry with Focus on New Materials, Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, D-85747 Garching, GermanySearch for more papers by this authorJonathan G. C. Veinot, Jonathan G. C. Veinot Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 CanadaSearch for more papers by this authorBernhard Rieger, Bernhard Rieger WACKER-Chair of Macromolecular Chemistry, Catalysis Research Center, Technical University of Munich, Lichtenbergstraße 4, 85758 Garching, GermanySearch for more papers by this author Marc Julian Kloberg, Marc Julian Kloberg WACKER-Chair of Macromolecular Chemistry, Catalysis Research Center, Technical University of Munich, Lichtenbergstraße 4, 85758 Garching, GermanySearch for more papers by this authorHaoyang Yu, Haoyang Yu Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 CanadaSearch for more papers by this authorElisabeth Groß, Elisabeth Groß WACKER-Chair of Macromolecular Chemistry, Catalysis Research Center, Technical University of Munich, Lichtenbergstraße 4, 85758 Garching, GermanySearch for more papers by this authorFelix Eckmann, Felix Eckmann Chair of Experimental Semiconductor Physics II, Walter Schottky Institute and Physics Department, Technical University of Munich, Am Coulombwall 4, 85748 Garching, GermanySearch for more papers by this authorTassilo M. F. Restle, Tassilo M. F. Restle Chair for Inorganic Chemistry with Focus on New Materials, Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, D-85747 Garching, GermanySearch for more papers by this authorThomas F. Fässler, Thomas F. Fässler Chair for Inorganic Chemistry with Focus on New Materials, Department of Chemistry, Technische Universität München, Lichtenbergstraße 4, D-85747 Garching, GermanySearch for more papers by this authorJonathan G. C. Veinot, Jonathan G. C. Veinot Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2 CanadaSearch for more papers by this authorBernhard Rieger, Bernhard Rieger WACKER-Chair of Macromolecular Chemistry, Catalysis Research Center, Technical University of Munich, Lichtenbergstraße 4, 85758 Garching, GermanySearch for more papers by this author First published: 21 September 2021 https://doi.org/10.1002/adma.202170296AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Quantum Dots In article number 2100288, Marc Julian Kloberg, Bernhard Rieger, and co-workers deposit quantum dots onto a 2D substrate (honeycomb lattice with buckling), which, upon irradiation with light, are released from the surface while the underlying substrate is destroyed. The final product is Janus particles with two chemically different faces. Volume33, Issue38September 23, 20212170296 RelatedInformation

Surface-anisotropic nanoparticles represent a new class of materials that shows potential in a variety of applications, including self-assembly, microelectronics, and biology. Here, the first synthesis of surface-anisotropic silicon quantum dots (SiQDs), obtained through masking on 2D silicon nanosheets, is presented. SiQDs are deposited on the 2D substrate, thereby exposing only one side of the QDs, which is functionalized through well-established hydrosilylation procedures. The UV-sensitive masking substrate is removed through UV-irradiation, which simultaneously initiates the hydrosilylation of a second substrate, thereby introducing a second functional group to the other side of the now free-standing SiQDs. This renders surface-anisotropic SiQDs that have two different functional groups on either side of the particle. This method can be used to introduce a variety of functional groups including hydrophilic and hydrophobic substrates, while the unique optoelectronic properties of the SiQDs remain unaffected. The anisotropic morphology of the QDs is confirmed through the aggregation behavior of amphiphilic Janus SiQDs at the interface of water and hexane. Additionally, anisotropic SiQDs are used to produce the first controlled (sub)monolayer of SiQDs on a gold wafer.

Solution-processed thin films of crystalline silicon nanoparticles (Si NPs) have a great potential for a wide variety of electronic and optoelectronic applications. However, such films are inherently unstable due to their huge surface-to-volume ratios and high surface energies, making them prone to degradation associated with spontaneous oxidation in ambient conditions. In this work, we explore the use of atomic layer deposition (ALD) as a means to stabilize and potentially functionalize solution-processed thin films of Si NPs for (opto)electronics, e.g., thin-film transistors, photosensors, light-emitting devices, and photovoltaics. We prepared films of randomly distributed Si NPs with ultrashort surface ligands (Si-H termination) using wet chemistry and spray-coating and then use ALD to infill the films with Al2O3. Through microscopy and optical structural/morphological analysis, we demonstrate the achievability of ALD infilling of films of Si NPs and probe the stability of these films against oxidation. Moreover, we show that the ALD infilling leads to changes in the light emission properties of the Si NP films, including a relative quenching of disorder-related emission features and variations in surface-related dielectric confinement effects. Our studies reveal ALD as a relevant technique toward manufacturing de facto robust, functional nanomaterials based on Si NPs and on nanoscale silicon materials more generally.

Research on optically resonant dielectric nanostructures has accelerated the development of photonic applications, driven by their ability to strongly confine light on the nanoscale. However, as dielectric resonators are typically operated below their band gap to minimize optical losses, the usage of dielectric nanoantenna concepts for absorption enhancement has largely remained unexplored. In this work, we realize engineered nanoantennas composed of photocatalytic dielectrics and demonstrate increased light-harvesting capabilities in otherwise weakly absorptive spectral regions. In particular, we employ anapole excitations, which are known for their strong light confinement, in nanodisks of oxygen-vacancy-rich TiO2-x, a prominent photocatalyst that provides a powerful platform for exploring concepts in absorption enhancement in tunable nanostructures. The arising photocatalytic effect is monitored on the single particle level using the well-established photocatalytic silver reduction reaction on TiO2. With the freedom of changing the optical properties of TiO2 through tuning the abundance of VO states, we discuss the interplay between cavity damping and the anapole-assisted field confinement for absorption enhancement. This concept is general and can be extended to other catalytic materials with higher refractive indices.

Nanowire (NW) based devices for solar driven artificial photosynthesis have gained increasing interest in recent years due to the intrinsically high surface to volume ratio and the excellent achievable crystal qualities. However, catalytically active surfaces often suffer from insufficient stability under operational conditions. To gain a fundamental understanding of the underlying processes, the photochemical etching behavior of hexagonal and round GaN NWs in deionized water under illumination are investigated. We find that the crystallographic c-plane remains stable, whereas the m-planes are photochemically etched with rates up to 11 nm min-1, depending on the applied UV light intensity. By investigating nanowalls, we achieve control of the exposed crystallographic facets and find an enhanced stability of the a-plane compared to the m-plane. Photo-excited holes, which drift to the side facets due to the upward surface band bending in nominally n-type (not intentionally doped) GaN, are identified as the driving force of the process, which allows the development of concepts for the stabilization of the nanostructures. A geometrically enhanced absorption of periodic NW arrays is correlated with a dependence of the etch rate on the NW pitch and diameter. Further, we find selective photochemical etching of the NW base in the presence of sub-band gap illumination, which is attributed to defect-related absorption in this region. These results provide improved understanding of the roles of inhomogeneous defect distribution, light excitation profiles, and different surface facets on the photochemical stability of nanostructures and provide viable strategies for improving stabilities under light-driven reaction conditions.