UV-activated alkyne-alkene [2 + 2] cycloaddition has served as an important tool to access cyclobutenes. Although broadly adopted, the limitations with UV light as an energy source prompted us to explore an alternative method. Here we report alkyne-alkene [2 + 2] cycloaddition based on visible light photocatalysis allowing the synthesis of diverse cyclobutenes and 1,3-dienes via inter-and intramolecular reactions. Extensive mechanistic studies suggest that the localized spin densities at sp 2 carbons of alkenes account for the productive sensitization of alkenes despite their similar triplet levels of alkenes and alkynes. Moreover, the efficient formation of 1,3-dienes via tandem triplet activation of the resulting cyclobutenes is observed when intramolecular enyne cycloaddition is performed, which may serve as a complementary means to the Ru(II)-catalyzed enyne metathesis. In addition, the utility of the [2 + 2] cycloaddition has been demonstrated by several synthetic transformations including synthesis of various extended π-systems.

A luminescent solar concentrator (LSC)-based photovoltaic (PV) system, consisting of an LSC panel that harvests light and an edge-mounted solar cell that produces electricity using the photoluminescent light, is promising for semitransparent building-integrated photovoltaics (BIPVs). Here, we demonstrate a highly efficient and highly semitransparent LSC-PVs capable of harvesting dual wavelength bands. We used a triplet−triplet annihilation-based photon upconversion (UC) LSC that luminesce high energy green light by absorbing low energy red light, as well as downshift LSC that luminesce green light by absorbing ultraviolet light. The luminescent light concentrated from the two LSCs is absorbed by a dye-sensitized solar cell (DSSC) having a high extinction coefficient at this wavelength. Our optimized dual band LSC-PV exhibited 27% higher power conversion efficiency than the LSC-PV that absorb a single wavelength band. With respect to practical applications, the dual band LSC-DSSCs were fabricated in the form of an LSC window-DSSC window frame. We achieved a power conversion efficiency of 9.1% per LSC panel area. This dual-band LSC-DSSC exhibited high stability and maintained efficiency even at oblique illumination. Our results will be promising as an aesthetic and energy independent next generation BIPV.

The effectiveness of the 1D nanorod (NR)-planted 3D inverse opal (IO) structure as an electrode for dye-sensitized solar cells (DSSCs) is demonstrated here. The NRs were grown on the surface of a macroporous IO structure and their longitudinal growth increased the surface area of the structure proportional to the growth duration. NR/IO electrodes with various NR growth times were compared. A remarkable JSC was obtained for the DSSCs utilizing a NR/IO electrode. The improvement of the JSC was analyzed in terms of its efficiency in light harvesting and electron transport. The growth of the NRs improved the dye adsorption density and scattering property of the electrode, resulting in an improvement in the light harvesting efficiency. Electrochemical impedance analysis revealed that the NRs also improved its electron transport properties. Further growth of the NRs tended to limit the increase of the JSC, which could be attributed to an overlap between them.

This Feature Article introduces the preparation and synthetic utility of α-diazo oxime ethers. α-Oximino carbenes are useful synthons for N-heterocycles, and can be easily prepared from α-diazo oxime ethers as precursors. We begin with the preparation of α-diazo oxime ethers and their application in [3+2] cycloaddition. It turns out that the nature of metals bound to carbenes plays a crucial role in modulating the reactivity of α-oximino carbenes, in which copper carbenes smoothly react with enamines, whereas the less reactive enol ethers and nitriles require gold carbenes. In Section 3.2, a discussion on N-O and C-H bond activation is presented. Carbenes derived from diazo oxime ethers show unique reactivity towards N-O and C-H bond activation, in which the proximity of the two functionalities, carbene and oxime ether, dictates the preferred reaction pathways toward pyridines, pyrroles, and 2H-azirines. In Section 3.3, the development of tandem reactions based on α-diazo oxime ethers is discussed. The nature of carbenes in which whether free carbenes or metal complexes are involved dissects the pathway and forms different types of 2H-azirines. The 2H-azirine formation turned out to be an excellent platform for the tandem synthesis of N-heterocycles including pyrroles and pyridines. In the last section, we describe the electrophilic activation of 2H-azirines with vinyl carbenes and oximino carbenes. The resulting azirinium species undergo rapid ring expansion rearrangements to form pyridines and pyrazines.

Dye-sensitised solar cells (DSCs) are a promising substitute for conventional silicon solar cells. A scattering layer of submicrometer pores or particles has been widely introduced to achieve a high light-harvesting efficiency. However, many such fabrication processes require high temperatures and multiple steps to prepare the scattering layer. Here, we have developed an in-situ fabrication process for a macroporous (MP) scattering film. The macropores were formed inside the assembled cell via the dissolution of polystyrene (PS) spheres from a PS/TiO2 composite layer caused by exposure to an electrolyte solution. Specifically, the in-situ MP scattering layer decreased the transmittance of the electrode film from 58% to below 1%. The DSCs using these MP scattering layers exhibited an increase in the efficiency of 22%. Moreover, the dissolution of the PS improved the cell stability because of the gelation of the electrolyte solution; the efficiency of the DSCs was maintained at 80% of its initial value after ageing for 20 days, whereas the efficiency of the bare-electrode DSCs was found to have decreased by 50%. We believe that in-situ porous scattering layers show great promise for next-generation flexible DSCs. Moreover, this approach can be extended to various applications that utilize porous film/liquid systems.