The recent discovery that metal nanoparticles can generate hot carriers upon light excitation is seen as a breakthrough in the fields of plasmonics and photonics. However, the high expectations for a plasmonic revolution in applications have been dampened by the ultrafast energy dissipation of surface plasmon polariton modes. While research aimed at suppressing loss mechanisms is still pursued, another research direction has emerged where charges are harnessed before they relax. Despite the effort, efficiencies of devices based on hot carriers harnessed from plasmonics are typically very low (a few percent), which is somehow paradoxical since efficiencies for electron injection efficiency have been reported to be in the range from 25% to 40% and hole injection up to 85%. This indicates that the low device performance relates to the undesirable charge back-transfer process, which happens in the picosecond time scale. In this context, we performed a comparative ultrafast spectroscopy investigation with gold nanoparticles in direct contact with different metal oxides, namely, TiO2, ZnO, SnO2, and Al:ZnO. Electron dynamics revealed the decisive role of metal/semiconductor interfaces and semiconductor electronic structure in electron injection efficiency and recombination, with significant implications to the fields of photocatalysis and photovoltaics.

Hydrated electrons are important in radiation chemistry and chargetransfer reactions, with applications that include chemical damage of DNA, catalysis, and signaling. Conventionally, hydrated electrons are produced by pulsed radiolysis, sonolysis, two-ultraviolet-photon laser excitation of liquid water, or photodetachment of suitable electron donors. Here we report a method for the generation of hydrated electrons via single-visible-photon excitation of localized surface plasmon resonances (LSPRs) of supported sub-3 nm copper nanoparticles in contact with water. Only excitations at the LSPR maximum resulted in the formation of hydrated electrons, suggesting that plasmon excitation plays a crucial role in promoting electron transfer from the nanoparticle into the solution. The reactivity of the hydrated electrons was confirmed via proton reduction and concomitant H2 evolution in the presence of a Ru/ TiO2 catalyst.

CsPbBr 3 quantum dots (QDs) are promising candidates for optoelectronic devices. The substitution of oleic acid (OA) and oleylamine (OLA) capping agents with a quaternary alkylammonium such as di-dodecyl dimethyl ammonium bromide (DDAB) has shown an increase in external quantum efficiency (EQE) from 0.19% (OA/OLA) to 13.4% (DDAB) in LED devices. The device performance significantly depends on both the diffusion length and the mobility of photoexcited charge carriers in QD solids. Therefore, we investigated the charge carrier transport dynamics in DDAB-capped CsPbBr 3 QD solids by constructing a bi-sized QD mixture film. Charge carrier diffusion can be monitored by quantitatively varying the ratio between two sizes of QDs, which varies the mean free path of the carriers in each QD cluster. Excited-state dynamics of the QD solids obtained from ultrafast transient absorption spectroscopy reveals that the photogenerated electrons and holes are difficult to diffuse among small-sized QDs (4 nm) due to the strong quantum confinement. On the other hand, both photoinduced electrons and holes in large-sized QDs (10 nm) would diffuse toward the interface with the small-sized QDs, followed by a recombination process. Combining the carrier diffusion study with a Monte Carlo simulation on the QD assembly in the mixture films, we can calculate the diffusion lengths of charge carriers to be ∼239 ± 16 nm in 10 nm CsPbBr 3 QDs and the mobility values of electrons and holes to be 2.1 (± 0.1) and 0.69 (± 0.03) cm 2 /V s, respectively. Both parameters indicate an efficient charge carrier transport in DDAB-capped QD films, which rationalized the perfect performance of their LED device application.