Short Wavelength Region Research Articles

SnHPO4: A Layered Tin(II) Phosphate with Enhanced Birefringence.

As promising optoelectronic functional materials in the short-wavelength spectral region, such as ultraviolet (UV) and deep UV, phosphates have recently received increased attention. However, phosphate materials commonly suffer from limited birefringence owing to the highly symmetrical PO4 tetrahedra. We herein report a layered tin(II) phosphate with improved birefringence. By employing a polarizing microscope, the measured refractive index difference determined on a (010) wafer is 0.042@550 nm, which is very close to the calculated refractive index difference of 0.039@550 nm between nx and nz through the density functional theory (DFT) method. The largest birefringence appears on the (100) plane, which is theoretically determined to be 0.078@550 nm. Single crystals of SnHPO4 measuring 20 × 4 × 3 mm3 can be easily grown by a hydrothermal method. In addition, SnHPO4 is UV transparent with a short UV absorption cutoff edge of 242 nm and an optical band gap of 4.50 eV, implying that it could be a potential UV birefringent material.

Evolution from 3-D to 2-D of a confined hydrogen atom dipole dependent properties when compressed by two parallel planes

Abstract The confinement of an atom by two parallel planes produces changes in the spectra and dipole-dependent electronic properties when evolving from large – 3-D – to narrow – 2-D – inter-plane separation. In this work, the behavior of the dipole electronic properties of a hydrogen atom located half the distance between two impenetrable parallel planes is studied as a function of the inter-plane separation
using the energies and wave functions reported previously by the author [Physica Scripta 99, 065416 (2024)]. The evolution of the line intensities, transition rates, life times, polarizability, and the mean excitation energy are reported as a function of the inter-plane separation. We find that as the inter-plane separation is reduced, all the electronic properties are affected by the shifting of the electronic spectra towards the short wave-length region (EUV) with a boost of the photo-luminosity intensity, reduction of the static polarizability and life-time of the 2s and 2p states, increase of the mean excitation energy, and transition rates for characteristic plane separations. Our numerical results agree, in the limiting cases, to the analytical solutions for a free atom for large inter-plane separations and to those of a 2-D atom for small inter-plane separation, as well as to available experimental data.

Bifunctional Design of Ferroelectric-Order and Band-Engineering in Cu:KTN Crystal for Extended Self-Powered Photoelectric Response.

Photoelectric conversion in ferroelectric crystals can support many important applications in modern on-chip technology, but suffering from two problems, low responsive current and narrow responsive range. Especially, wide-gap ferroelectric oxides are only active at short-wavelength ultraviolet region with weak photocurrent at nanoampere levels. Here, a bifunctional design strategy of ferroelectric-order and electronic-band to improve the photocurrent and extend the responsive range simultaneously, is proposed. In a Cu-doped KTa1- xNbxO3 (KTN) perovskite crystal, a conductive channel is constructed by "head-to-head" ferroelectric domains, associated with the emergence of micrometer-scale supercells. In addition, the introduction of Cu+ ion can induce defect levels, thus extending the responsive range beyond the inherent absorption of pure KTN. Through rational device optimization, a record self-powered responsivity of 5.23 mA W-1 is realized in Cu:KTN photodetector, which is two orders of magnitude higher than undoped KTN crystal. The temperature-dependent light diffraction and photocurrent show that the ferroelectric-order is dominated in this photoresponse behavior. Moreover, Cu:KTN detector is active in the broadband range from 390 to 1030 nm, covering ultraviolet, visible, and near-infrared regions. This work provides an effective method for the design of next-generation self-powered photodetectors with ultrahigh responsivity and ultrawide responsive range.

The New Paradigm of Ligand Substitution-Driven Enhancement of Anisotropy from SO4 Units in Short-Wavelength Region.

For non-π-conjugated [SO4] units, it is challenging to generate sufficient birefringence, owing to the high symmetry of the regular tetrahedron. Unlike the traditional trial-and-error approach, we propose a new paradigm for birefringence engineering to tune the optical properties based on [SO4] units. Through the strategy of ligand substitution, we can predict its effect on the band gap and anisotropy. Theoretical evaluations reveal generalized results that the anisotropic electron distribution of new functional groups induced by the suitable ligand substitution contributes to the band gap and birefringence. To further validate the correctness of the paradigm, we experimentally synthesized and characterized nine novel compounds with selected functional modules. By the new paradigm of ligand substitution, they can reach up to 4-6 times the birefringence of the corresponding sulfate and maintain the wide bandgap. Through rational design, (CN4H7)SO3NH2 exhibits about 35 times the birefringence of Li2SO4, which is a significant order of magnitude improvement and verifies the superiority of our proposed paradigm. This work provides a new paradigm for the modification to the non-π-conjugated group and will guide and accelerate the exploration of novel birefringent crystals in the short-wavelength region.

Induced Emission on Transitions from Vibrational Excited Levels of the KrF Molecule

The paper considers the possibility of extending the spectral region of the wavelength tuning of a discharge KrF amplifier due to induced transitions from the vibrational excited states of the electronic level B. The model of the KrF amplifier on a He/Kr/F2 mixture is presented, in which the behavior of the vibrational level populations is consistent with the excitation conditions of the active medium. The simulation results show that the shift in the operating wavelength to the short-wavelength region is possible in excitation modes, when the birth rate of excimer molecules is greater than the rate of their relaxation from upper to lower vibrational levels. The theoretical dependences of gain on the wavelength for different pressures were obtained. They confirm the possibility of tuning the KrF amplifier wavelength in the range of up to 10 nm while maintaining a gain of at least 0.5 of its maximum value.

Comparative analysis of theories accounting for quantum effects in plasmonic nanoparticles

Understanding and accounting for quantum effects in nanoplasmonics is essential for accurate modeling and design of nanophotonic devices. In this paper, we investigate the influence of such quantum effects as spatial nonlocality and splitting of the wave function of conduction electrons near the surface of plasmonic nanoparticles on the extinction cross-section and the field enhancement factor. We apply the theory of generalized nonlocal optical response (GNOR) to describe the spatial nonlocality of noble metal particles. To consider the behavior of electrons near the metal–dielectric interface, mesoscopic boundary conditions are used, including the surface response functions (SRF) - the Feibelman parameters. We use the discrete source method (DSM), allowing for numerical analysis of the scattering problems taking into account quantum effects in the frame of both theories. The application of both GNOR and SRF approaches leads to a decrease in the amplitude of the plasmon resonance compared to the classical Maxwell theory and its shift to the shorter wavelength region (blue shift). The simulation results demonstrate significant differences between the two theories explaining the quantum effects arising in non-spherical plasmonic nanoparticles located in a dense environment. Specifically, compared with GNOR theory, SRF predicts a larger field enhancement. We found that quantum nonlocal effects are more significant for the enhancement factor at the particle surface than for the extinction cross-section. In addition, it was discovered that a denser environment leads to a significant increase in the blue shift of the plasmonic peak.

Investigation of inter-dot tunnelling effect in hybrid coupled QDs heterostructures for short-wave infrared detection (SWIR) application

This paper explores the coupling between two different types of dots for enhancing the performance of p type/hole based (p-i-p) quantum dot infrared photodetectors (QDIPs). There are two possible con: Stranski-Krastanov (SK) QDs can be deposited on submonolayer (SML) QDs, or the SML QDs can be deposited first, followed by SK QDs. Here, both configurations are tried, and the fact that the tunnelling improves with a decrease in the barrier is exploited. The tunnelling of carriers from one QD to another QD is facilitated by the overlap of their wavefunctions, which depends on their spatial separations between the dots. A smaller barrier will lead to enhanced tunnelling probability. Utilising this idea, samples with 20 nm and 7.5 nm barriers between the QDs are grown with both types of configurations. An enhancement is anticipated in the absorption and carrier lifetime of the p-i-p QDIP structures, making them well-suited for detection in short-wavelength infra-red regions. The p-i-p configuration with the active layers of coupled QDs sandwiched between p-type dopped layers, can effectively absorb SWIR photons and generate long-lived carriers for improved photodetection performance. With the help of Photoluminescence (PL), Photoluminescence Excitation (PLE), and X-ray Diffraction (XRD) experiments, we expect large dispersion in SK on SML configuration, significantly improved carrier transfer via tunnelling and thermalisation and, changes in dot density for both of the configurations. Development of a more efficient SWIR device is expected by the insightful understanding of carrier transfer by tunnelling and thermalization with respect to the barrier thickness in the coupled QD based heterostructures.

Comparison between consumer-oriented and laboratory benchtop near-infrared spectrometers for total soluble solids measurement in grape

Portable near-infrared (NIR) spectrometers are gaining interest as a non-destructive tool for fruit quality determination in the decade. In this study, the performance of the portable NIR spectrometer for TSS prediction of grapes was evaluated and compared to the benchtop spectrometer. A total of 105 table grapes were individually measured NIR spectra at short-wavelength (740 – 1070 nm) and long-wavelength NIR region (1000 – 2500 nm) using SCiO and NIRFlex N-500 spectrometers, respectively. Partial least square (PLS) regression analysis was performed on berry spectra from both devices afterward significant wavelengths were identified and used to develop multiple linear regression (MLR) models. The best PLS prediction model was obtained from SNV pretreating spectra for both devices and spectral data acquired from SCiO showed better prediction performance (= 0.854, SEP = 0.452°Brix) than NIRFlex N-500 spectra (= 0.667, SEP = 0.675°Brix). Low predicting ability was gained for the MLR calibration model for both device with an RPD of about 1.70. From the results, a pocket-size spectrometer has the potential to be a non-destructive sorting and screening tool in fruit industries.

In situ high-temperature emissivity measurements of heat-treated, silicon coated stainless steel for solar thermal applications

Understanding thermal emissivity at high temperatures is crucial for developing efficient materials for solar thermal applications. We present a new approach for creating an efficient material for solar absorber by developing a nano structured surface on stainless steel substrate through Si deposition and annealing. We prepare five samples by annealing them at five temperatures between 700 °C and 1100 °C. Afterwards, we perform a systematic study of the spectral emissivity at elevated temperatures, focusing on different parameters: angle dependence, wavelength dependence, and temperature dependence. The spectral directional emissivity experiments performed in the mid-infrared range reveal a dielectric behavior of the samples in the short wavelength region (λ < 6 μm) and metallic behavior in the long wavelength region (λ > 12 μm). The results indicate an increase in hemispherical and total normal emissivity with measurement temperature (from 200 °C to 700 °C), influenced by oxide/silicide formation due to interdiffusion, and by surface roughness. Notably, samples annealed at 900 °C and 1000 °C demonstrate enhanced thermal stability at 700 °C, showcasing promising characteristics for high-temperature applications. Consequently, this study presents a viable method for developing cost-effective silicon-based solar absorber coatings on stainless steel with tailored properties for solar thermal applications along with its real time high temperature emissivity details.

Modeling of the tunable plasmonic properties of spherical and ellipsoidal silver nanoparticles in the matrix of an organic semiconductor

The object of research is the tunable plasmonic properties of spherical and ellipsoidal silver nanoparticles in the organic semiconductor matrix. The average absorption cross-sections, scattering cross-sections, and optical radiation efficiency of spherical and ellipsoidal silver nanoparticles have been simulated. The long-wave statistical approach has been used to model the optical parameters of the assembled spherical and ellipsoidal nanoparticles. Statistical averaging is used here, where absorption and scattering are considered from an «effective» particle with statistical properties. This approach avoids complex calculations considering the details of the spectral characteristics of single nanoparticles of different shapes. Taking into account the fact that the nanocomposite matrix will contain ensembles of spherical nanoparticles of different sizes, the peak of their absorption and scattering cross sections will be shifted to the short wavelength region of the spectrum compared to ensembles of the same spherical nanoparticles. In addition, there is a slight increase in the absorption cross-section and a decrease in the scattering cross-section, confirming the presence of smaller nanoparticles. A study was made of a composite material containing a randomly dispersed ensemble of silver ellipsoidal nanoparticles of the same and different shapes and sizes in an organic semiconductor matrix. An ensemble of identical ellipsoidal nanoparticles is characterized by the presence of two plasmon peaks, which corresponds to the characteristics of a single ellipsoidal nanoparticle. A completely different situation is observed if to consider that the nanocomposite will contain an ensemble of ellipsoidal nanoparticles of different shapes and sizes. Such nanoparticles will be characterized by a plasmon peak for both the absorption and scattering cross-sections. This can be explained by the fact that as the size of ellipsoidal nanoparticles decreases, the distance between the peaks responsible for the longitudinal and transverse modes of plasmon excitation decreases. An increase in the shape distribution leads to a broadening of the absorption and scattering cross-section spectra. The efficiency of the optical radiation increases as the size distribution increases. It is shown that a change in the refractive index of an organic semiconductor matrix mainly affects only the value of the scattering cross-section of an ensemble of ellipsoidal nanoparticles dispersed in it. This research is a preliminary step to studying the influence of these particles on the properties of organic light-emitting structures.

(GaAs/InAs)–GaAsSb digital alloy type-II superlattice for extended short-wavelength infrared detection

GaInAs–GaAsSb type-II superlattices (T2SLs) on an InP substrate are promising candidates for an optical absorption layer in the extended short-wavelength region (2–3 μm), offering more flexibility in designing a cutoff wavelength compared to strained GaInAs bulk material. However, T2SL-based photodetectors inherently suffer from lower quantum efficiency (QE) due to the reduced overlap of the wavefunctions of the conduction and valence bands in the optical matrix element of the T2SL. To improve QE, a (GaAs/InAs)–GaAsSb digital alloy T2SL, which replaces the GaInAs random alloy layer in the GaInAs–GaAsSb T2SL with a GaAs/InAs digital alloy, has been proposed recently by an empirical tight-binding calculation. This paper presents a demonstration of a fabricated photodetector using the (GaAs/InAs)–GaAsSb digital alloy grown on an InP substrate by molecular beam epitaxy and shows that the average QE in the wavelength region of 2.3–2.6 μm is approximately 1.6 times higher than that of a conventional GaInAs–GaAsSb T2SL photodetector. Furthermore, the dark-current density of the digital alloy photodetector is lower than that of the GaInAs–GaAsSb T2SL photodetector despite having a longer cutoff wavelength.

Analytical Spectral Semi-quantitative Dating Method of Printed Text Toner Using Raman Spectroscopy and the Fluorescence signal of Paper Sheet Cellulose

Abstract: The chemical processes that occur during the surface degradation of document paper under the influence of external factors were studied by Raman spectroscopy. The possibility of comparing the same processes occurring on clean free paper and under printed text toner letters is of interest. It is assumed that the transformation of cellulose can occur at different rates in the areas of paper exposed to direct atmospheric and light exposure and in the areas containing an intermediate layer of the toner. The most stable temporal changes occur in the region of C–C–C and C– C–O vibrations of glycosidic rings in the short-wavelength region of the Raman spectrum. Background: The main areas of research in the field of document dating, mainly focused on chromatographic methods. These methods are based on studying the dynamics of evaporation of volatile ink components. There is also a variety of chromatography techniques, including gas chromatography, ion chromatography, high performance liquid chromatography, thin layer chromatography and gas chromatography-mass spectrometry. This indicates the wide range of approaches and techniques used to determine the age of written materials. However, all these methods are used mainly during the first two years after writing the document details, which does not allow examining documents that are more than two years old. Methods: Raman spectroscopy was used as the main research method. The object of the study was sheets of white A4 paper with printed text printed on them, produced on a laser printer. The subject of the study was areas of paper free of text, as well as areas of paper under toner. The integrated fluorescence of a paper optical brightener based on stilbene was studied in the wavelength range of 400–500 nm. Also, all objects were studied using optical microscopy. Results: The comparison of peak intensity values averaged over 10 brands over the years made it possible to reveal the following regularities: – the ratio of peaks in the paper spectra from which the toner was removed is greater than in the blank paper spectra, and the difference becomes less noticeable as the age of the paper decreases. The ratio of the intensity of the 330 cm-1 peak to the intensity of the 1603 cm-1 peak: the older the document becomes, the lower the average ratios of these peaks in both the blank paper spectra and in the spectra of paper from which the toner has been removed. –the intensity of the peak in the region of 280 cm-1 and 1 086 cm-1 of the Raman shift increases with decreasing the age of the toner-free paper.– a gradual increase in the intensity of the 380 cm-1 peak is observed when comparing the paper samples from which the toner was removed for 2016, 2018, 2020, and 2022. Regularity was also found in the change in the ratio of the average statistical values of the peak at 280 cm-1 in the spectra of the paper under the toner to a similar peak in the spectra of the paper free from text: the value of this ratio decreases with decreasing the paper age. At the same time, the paper fluorescence signal is an informative parameter that makes it possible to establish some facts from the document’s history. With artificial document aging, a significant broadening of the dispersion region and the appearance of its “splitting” into two or three strata are observed in the distribution of the fluorescence signal level of a paper sheet relative to the average value. The average fluorescence signal of a naturally aged sheet decreases with the age of the document. Conclusion: As a result of research, it has been established that Raman spectroscopy can be successfully used as a method for dating documents. When comparing the degree of degradation of the surface of open areas of paper and areas protected by toner of printed text, different effects of external factors on these areas were established, leading to different rates of degradation processes. The use of Raman peak intensity ratios for paper components in exposed areas compared to peaks under printed text further expands the methodology. The emphasis on spectral methods, in particular fluorescence signal distribution and Raman spectroscopy, to detect surface changes is well justified. It demonstrates a holistic approach to document analysis, taking into account both the chemical changes observed using Raman spectroscopy and the fluorescence signal distribution that may indicate signs of artificial aging through light exposure. This combination of methods appears to be reliable for assessing the age of documents and can make significant contributions to the field of forensic document examination.

In-silico predicted mouse melanopsins with blue spectral shifts deliver efficient subcellular signaling

Melanopsin is a photopigment belonging to the G Protein-Coupled Receptor (GPCR) family expressed in a subset of intrinsically photosensitive retinal ganglion cells (ipRGCs) and responsible for a variety of processes. The bistability and, thus, the possibility to function under low retinal availability would make melanopsin a powerful optogenetic tool. Here, we aim to utilize mouse melanopsin to trigger macrophage migration by its subcellular optical activation with localized blue light, while simultaneously imaging the migration with red light. To reduce melanopsin’s red light sensitivity, we employ a combination of in silico structure prediction and automated quantum mechanics/molecular mechanics modeling to predict minimally invasive mutations to shift its absorption spectrum towards the shorter wavelength region of the visible spectrum without compromising the signaling efficiency. The results demonstrate that it is possible to achieve melanopsin mutants that resist red light-induced activation but are activated by blue light and display properties indicating preserved bistability. Using the A333T mutant, we show that the blue light-induced subcellular melanopsin activation triggers localized PIP3 generation and macrophage migration, which we imaged using red light, demonstrating the optogenetic utility of minimally engineered melanopsins.

Scalable CIGS Solar Cells Employing a New Device Design of Nontoxic Buffer Layer and Microgrid Electrode.

The efficiency of copper indium gallium selenide (CIGS) solar cells that use transparent conductive oxide (TCO) as the top electrode decreases significantly as the device area increases owing to the poor electrical properties of TCO. Therefore, high-efficiency, large-area CIGS solar cells require the development of a novel top electrode with high transmittance and conductivity. In this study, a microgrid/TCO hybrid electrode is designed to minimize the optical and resistive losses that may occur in the top electrode of a CIGS solar cell. In addition, the buffer layer of the CIGS solar cells is changed from the conventional CdS buffer to a dry-processed wide-band gap ZnMgO (ZMO) buffer, resulting in increased device efficiency by minimizing parasitic absorption in the short-wavelength region. By optimizing the combination of ZMO buffer and the microgrid/TCO hybrid electrode, a device efficiency of up to 20.5% (with antireflection layers) is achieved over a small device area of 5 mm × 5 mm (total area). Moreover, CIGS solar cells with an increased device area of up to 20 mm × 70 mm (total area) exhibit an efficiency of up to 19.7% (with antireflection layers) when a microgrid/TCO hybrid electrode is applied. Thus, this study demonstrates the potential for high-efficiency, large-area CIGS solar cells with novel microgrid electrodes.

Luminescent boron carbon oxynitride phosphors: a cost-efficient strategy to boost solar cell spectral responsiveness

The incorporation of a Luminescent down-shifting (LDS) layer has emerged as a compelling approach for augmenting the light absorption sensitivity and power conversion efficiency of solar cells, particularly in the short-wavelength light spectrum. In this investigation, we propose the utilization of low-cost, environmentally benign Boron carbon oxynitride (BCNO) phosphors as a viable material for the enhancement of solar radiation absorption in the ultraviolet-blue range. We synthesized BCNO phosphors through a combustion method and conducted a comprehensive analysis of the structural and spectral attributes concerning the impact of temperature. The synthesized boron carbon oxynitride phosphors exhibit a hexagonal boron nitride structure, with an irregular shape and an average particle size of 2447.9 nm. The analysis of photoluminescence spectra reveals that BCNO phosphors effectively capture photons within the 300–500 nm wavelength range and subsequently re-emit them at longer wavelengths. This phenomenon aligns with the overarching goal of optimizing solar cell performance, as it is in the longer wavelength range that solar cells exhibit enhanced efficiency. These findings support the promising potential of BCNO phosphors as a compelling choice for deployment as an LDS layer material on the periphery of solar cells. By facilitating increased photon absorption in the short-wavelength region, BCNO phosphors have the capacity to significantly enhance device performance.

Efficiency of Cr3+ → Cr4+ conversion in YSAG:Cr ceramics

In this study, we investigated the influence of the position and quantitative content of scandium in YSAG:Cr on the efficiency of chromium cation valence conversion. YSAG:Cr ceramic powders were synthesized using the chemical precipitation method. It was determined that the microstructure of ceramics and the luminescent properties of YSAG:Cr4+ depend on the predominant position of scandium, whether it replaces octahedral or dodecahedral positions in the garnet crystal lattice. An increase in Scdod content contributed to a decrease in grain size and a shift of the emission peak of Cr4+ ions towards the short-wavelength region. Conversely, an increase in Scoct content led to an increase in grain size and a shift of the maximum of the luminescent band towards the long-wavelength region. It was found that increasing the quantitative content of scandium in the octahedral position in the garnet structure by up to 50 % enhances the efficiency of the conversion of Cr3+ to Cr4+, while an increase in the proportion of Scdod resulted in a decrease in conversion efficiency.

Using HawkEye Level-2 Satellite Data for Remote Sensing Tasks in the Presence of Dust Aerosol

This paper is the first to examine the operation of the HawkEye satellite in the presence of dust aerosol. The study region is the Black Sea. Dust transport dates were identified using visual inspection of satellite imagery, back-kinematic HYSPLIT trajectory analysis, CALIPSO aerosol stratification and typing maps, and the global forecasting model SILAM. In a comparative analysis of in-situ and satellite measurements of the remote sensing reflectance, an error in the atmospheric correction of HawkEye measurements was found both for a clean atmosphere and in the presence of an absorbing aerosol. It is shown that, on average, the dependence of the atmospheric correction error on wavelength has the form of a power function of the form from λ−3 to λ−9. The largest errors are in the short-wavelength region of the spectrum (412–443 nm) for the dust and dusty marine aerosol domination dates. A comparative analysis of satellite and in situ measurements of the optical characteristics of the atmosphere, namely the AOD and the Ångström parameter, was carried out. It is shown that the aerosol model used by HawkEye underestimates the Angström parameter and, most likely, large errors and outliers in satellite measurements are associated with this.

In-fiber chirped Fabry-Perot cavity for temperature sensing.

Measurement resolution and dynamic range of conventional optical fiber sensors are often mutually restricted. In this work, an in-fiber chirped Fabry-Perot cavity (interferometer) is proposed, for the first time to our knowledge, to resolve the conflict between the resolution and dynamic range. The chirped Fabry-Perot interferometer is constructed by two chirped fiber Bragg gratings inscribed in the opposite directions, resulting in a gradually varied (i.e., chirp) cavity length for different reflection wavelengths. As such, the interference spectrum exhibits high figure of merit (FOM) and large free spectrum range (FSR) at long and short wavelength regions, respectively, enabling high-resolution and large-dynamic-range measurement simultaneously. Temperature tests are then carried out to confirm the validity of the solution. The proposed sensing schema may be developed further and find vital applications in biomedicine fields such as endosomatic temperature monitoring of living bodies. The proposed concept of chirped Fabry-Perot interferometer can provide breakout ideas for other sensing scenarios where high-resolution and large-dynamic range are demanded and can be further generalized to other measurands or even free-space interference metrologies.

Effective Charge Collection of Electron Transport Layers for High-Performance Quantum Dot Infrared Solar Cells.

Infrared (IR) solar cells, capable of converting low-energy IR photons to electron-hole pairs, are promising optoelectronic devices by broadening the utilization range of the solar spectrum to the short-wavelength IR region. The emerging PbS colloidal quantum dot (QD) IR solar cells attract much attention due to their tunable band gaps in the IR region, potential multiple exciton generation, and facile solution processing. In PbS QD solar cells, ZnO is commonly utilized as an electron transport layer (ETL) to establish a depleted heterostructure with a QD photoactive layer. However, band gap shrinkage of large PbS QDs makes it necessary to tailor the behaviors of the ZnO ETL for efficient carrier extraction in the devices. Herein, the characteristics of ZnO ETL are efficiently and flexibly tailored to match the QD layer by handily adjusting the postannealing process of ZnO ETL. With a suitable temperature, the well-matched energy level alignment and suppressed trap states are simultaneously achieved in the ZnO ETL, effectively reducing the nonradiative recombination and accelerating the electron injection from the QD layer to ETL. As a consequence, a high-performance PbS QD photovoltaic device with power conversion efficiencies (PCEs) of 10.09% and 1.37% is obtained under AM 1.5 and 1100 nm filtered solar illumination, demonstrating a simple and effective approach for achieving high-performance IR photoelectric devices.

Supramolecular Chirality Achieved by Assembly of Small π-Molecules of Octahydrobinaphtols with Axial Chirality.

5,5',6,6',7,7',8,8'-Octahydro-1,1'-bi-2-naphthol (hbNaph) is an axially chiral molecule consisting of a smaller π-electronic system than that for 1,1'-bi-2-naphthol (BINOL). The absorption and circular dichroism (CD) bands of hbNaph appear in a shorter wavelength region below 310 nm, compared to those of BINOL, and its fluorescence is in the invisible UV region. However, increasing the concentration of hbNaph in solution up to 0.1 M results in its absorption edge gradually extending to longer wavelength, with a shoulder around 330 nm, and finally increasing to about 450 nm. At the same time, blue fluorescence is clearly observed, as well as a new CD band with the sign of the Cotton signals reversed from those obtained for dilute solutions. These results suggest that, at high concentrations, hbNaph forms chiral aggregates, in which π-electrons are delocalized over multiple molecules. To further understand how molecular axial chirality is transformed to supramolecular chirality, we attempted to construct aggregate models by simulating CD spectra using a time-dependent density functional theory. The only reasonable model obtained was that involving the counterclockwise R-enantiomer forming a clockwise helix, while the clockwise S-enantiomer forms a counterclockwise helix. We conclude, however, that, for such helixes, the most plausible model is densely packed and forms when the dihedral angle between the two phenol rings of hbNaph is acute, at around 75°, which reproduces the aggregate-induced CD sign inversion.