1.4% External Quantum Efficiency 988 nm Light Emitting Diode Based on Tin-Lead Halide Perovskite.

In recent years, metal halide perovskite-based light-emitting diodes (LEDs) have garnered significant attention as they display high quantum efficiency, good spectral tunability, and are expected to have low processing costs. When the peak emission wavelength is beyond 900 nm the interest is even higher because of the critical importance of this wavelength for biomedical imaging, night vision, and sensing. However, many challenges persist in fabricating these high-performance NIR LEDs, particularly for wavelengths above 950 nm, which appear to be limited by low radiance and poor stability.

Air-Stable Thin Films of Tin Halide Perovskite Nanocrystals by Polymers and AlO Encapsulation.

Tin halide perovskites are promising for optoelectronics, although their sensitivity to ambient conditions due to Sn(II) oxidation presents a challenge. Encapsulation techniques can mitigate degradation and facilitate advanced studies of the intrinsic properties. To study and improve the ambient stability of CsSnBr and CsSnI nanocrystal (NC) thin films, we explored various encapsulation methods: organic, inorganic, and hybrid.

Blade-coated perovskite nanoplatelet polymer composites for sky-blue light-emitting diodes.

Colloidal perovskite nanoplatelets (NPLs) have shown promise in tackling blue light-emitting diode challenges based on their tunable band gap and high photoluminescence efficiencies. However, high quality and large area dense NPL films have been proven to be very hard to prepare because of their chemical and physical fragility during the liquid phase deposition. Herein, we report a perovskite-polymer composite film deposition strategy with fine morphology engineering obtained using the blade coating method.

PbS Quantum Dots Ink with Months-Long Shelf-Lifetime Enabling Scalable and Efficient Short-Wavelength Infrared Photodetectors.

The phase-transfer ligand exchange of PbS quantum dots (QDs) has substantially simplified device fabrication giving hope for future industrial exploitation. However, this technique when applied to QDs of large size (>4 nm) gives rise to inks with poor colloidal stability, thus hindering the development of QDs photodetectors in short-wavelength infrared range. Here, it is demonstrated that methylammonium lead iodide ligands can provide sufficient passivation of PbS QDs of size up to 6.

Effects of the diphenyl ether additive in halogen-free processed non-fullerene acceptor organic solar cells.

The development of an environmentally friendly fabrication process for non-fullerene acceptor organic solar cells is an essential condition for their commercialization. However, devices fabricated by processing the active layer with green solvents still struggle to reach, in terms of efficiency, the same performance as those fabricated with halogenated solvents. The reason behind this is the non-optimal nanostructure of the active layer obtained with green solvents.

Crystallization driven boost in fill factor and stability in additive-free organic solar cells.

The control of morphology and microstructure during and after the active layer processing of bulk-heterojunction solar cells is critical to obtain elevated fill factors and overall good device performance. With the recent development of non-fullerene acceptors, wide attention has been paid to improve miscibility, solubility and nanoscale separation by laborious molecular design processes and by the use of additives. Nonetheless, several post-processing strategies can equally contribute to obtain an optimum phase separation and even to an enhanced crystallinity, but their effect on performance and device lifetime of polymer/non-fullerene acceptor solar cells is still unclear.

Measurement of the conformational switching of azobenzenes from the macro- to attomolar scale in self-assembled 2D and 3D nanostructures.

It is important, but challenging, to measure the (photo)induced switching of molecules in different chemical environments, from solution through thin layers to solid bulk crystals. We compare the cis-trans conformational switching of commercial azobenzene molecules in different liquid and solid environments: polar solutions, liquid polymers, 2D nanostructures and 3D crystals. We achieve this goal by using complementary techniques: optical absorption spectroscopy, femtosecond transient absorption spectroscopy, Kelvin probe force microscopy and reflectance spectroscopy, supported by density functional theory calculations.

Large-area, high-responsivity, fast and broadband graphene/n-Si photodetector.

A graphene/Si heterojunction device has been realized to overcome many different requests necessary to make it a versatile, widely used and competitive detector. The obtained photodetectors, which operate at room temperature, are sensitive in the spectral region from ultraviolet (240 nm) to infrared (2000 nm) and they can be used in different configurations that allow a high responsivity up to 10 A W, a rise time of a few nanoseconds, an external quantum efficiency greater than 300%, and a linear response for different light sources. This is allowed by the high quality of the graphene deposited on a large area of 8 mm, and by the interdigitated design of the contacts, both preserving the excellent properties of graphene when switching from nanoscale to macroscopic dimensions of commonly used devices.

Cobalt-Doped ZnO Nanorods Coated with Nanoscale Metal-Organic Framework Shells for Water-Splitting Photoanodes.

Developing highly efficient and stable photoelectrochemical (PEC) water-splitting electrodes via inexpensive, liquid phase processing is one of the key challenges for the conversion of solar energy into hydrogen for sustainable energy production. ZnO represents one the most suitable semiconductor metal oxide alternatives because of its high electron mobility, abundance, and low cost, although its performance is limited by its lack of absorption in the visible spectrum and reduced charge separation and charge transfer efficiency. Here, we present a solution-processed water-splitting photoanode based on Co-doped ZnO nanorods (NRs) coated with a transparent functionalizing metal-organic framework (MOF).

Ultrafast optical spectroscopy of semiconducting and plasmonic nanostructures and their hybrids.

The knowledge of the carrier dynamics in nanostructures is of fundamental importance for the development of (opto)electronic devices. This is true for semiconducting nanostructures as well as for plasmonic nanoparticles (NPs). Indeed, improvement of photocatalytic efficiencies by combining semiconductor and plasmonic nanostructures is one of the reasons why their ultrafast dynamics are intensively studied.

Ultrafast Formation of Small Polarons and the Optical Gap in CeO.

The ultrafast dynamics of excited states in cerium oxide are investigated to access the early moments of polaron formation, which can influence the photocatalytic functionality of the material. UV transient absorbance spectra of photoexcited CeO exhibit a bleaching of the band edge absorbance induced by the pump and a photoinduced absorbance feature assigned to Ce 4f → Ce 5d transitions. A blue shift of the spectral response of the photoinduced absorbance signal in the first picosecond after the pump excitation is attributed to the dynamical formation of small polarons with a characteristic time of 330 fs.

A Study of Photoinduced Coherent Vibrations in Gold-Nanorod Dispersions.

Upon photoexcitation with a femtosecond laser pulse, the plasmonic resonance of a nanorod can couple with coherent vibrational modes generating a regular oscillating pattern in the transient absorbance of the nanostructure. The dynamics of the plasmon resonances of these materials are probed through femtosecond transient absorption spectroscopy in the spectral region between 400 nm and 1600 nm. Whereas in the visible range the spectra are comparable with the findings reported in the literature, the analysis of the transient NIR spectra revealed that their oscillation frequencies vary with wavelength, resulting in a strong distortion of the transient features that can be related to the specific lengths distribution of the nanorods contained in the sample.

Plasmon-induced resonant effects on the optical properties of Ag-decorated ZnSe nanowires.

In this work we show how the optical properties of ZnSe nanowires are modified by the presence of Ag nanoparticles on the sidewalls of the ZnSe nanowires. In particular, we show that the low-temperature luminescence of the ZnSe nanowires changes its shape, enhancing the phonon replicas of impurity-related recombination and affecting rise and decay times of the transient absorption bleaching at room temperatures, with an increase of the former and a decrease of the latter. In contrast, the deposition of Au nanoparticles on ZnSe nanowires does not change the optical properties of the sample.

A Fast Transient Absorption Study of Co(AcAc).

The study of transition metal coordination complexes has played a key role in establishing quantum chemistry concepts such as that of ligand field theory. Furthermore, the study of the dynamics of their excited states is of primary importance in determining the de-excitation path of electrons to tailor the electronic properties required for important technological applications. This work focuses on femtosecond transient absorption spectroscopy of Cobalt tris(acetylacetonate) (Co(AcAc)) in solution.

Highly efficient plasmon-mediated electron injection into cerium oxide from embedded silver nanoparticles.

The coupling with plasmonic metal nanoparticles (NPs) represents a promising opportunity to sensitize wide band gap oxides to visible light. The processes which come into play after the excitation of localized surface plasmon resonances (LSPRs) in the NPs largely determine the efficiency of the charge/energy transfer from the metal NP to the oxide. We report a study of plasmon-mediated energy transfer from mass-selected silver NPs into the cerium oxide matrix in which they are embedded.

Carrier dynamics in silicon nanowires studied via femtosecond transient optical spectroscopy from 1.1 to 3.5 eV.

We present femtosecond transient transmission (or absorbance) measurements in silicon nanowires in the energy range 1.1-3.5 eV, from below the indirect band-gap to above the direct band-gap.

Direct growth of Si nanowires on flexible organic substrates.

A key characteristic of semiconductor nanowires (NWs) is that they grow on any substrate that can withstand the growth conditions, paving the way for their use in flexible electronics. We report on the direct growth of crystalline silicon nanowires on polyimide substrates. The Si NWs are grown by plasma-enhanced chemical vapor deposition, which allows the growth to proceed at temperatures low enough to be compatible with plastic substrates (350 °C), where gold or indium are used as growth seeds.