Light Absorption Coefficient Research Articles

Organolead Halide-Based Coordination Polymers: Intrinsic Stability and Photophysical Applications

ConspectusOrganolead halide-based photovoltaics are one of the state-of-the-art solar cell systems with efficiencies increasing to 25% over the past decade, ascribed to their high light-absorption coefficient, broad wavelength coverage, tunable band structure, and excellent carrier mobility. Indeed, these optical characteristics are highly demanding in photocatalysis and photoluminescence (PL), which also involve the solar energy utilization and charge transport. However, the vast majority of organolead halides are ionically bonded structures and susceptible to degradation upon high-polarity protic molecules (e.g., water (vapor) and alcohol), which are often inevitable in many photochemical applications. Encapsulation is a commonly used stabilization approach by coating protective layers, avoiding the direct contact between organolead halides and polar molecules. However, this may partially hinder the light penetration to the inner hybrid halide materials, and introduce new interface problems that are important in photocatalysis and luminescent sensing. Therefore, developing intrinsically stable organometal halide hybrids is a major target for their applications in optoelectronic applications.In this Account, recent research progress on the synthesis of organolead halide-based coordination polymers for a variety of photoactive applications is described. Herein, we propose a general strategy to advance the intrinsic stability of organometal halide crystalline materials by using coordinating anionic organic linkers, which occupy the excellent photophysical features analogous to those of perovskites. Unlike the organoammonium cations as for ionically bonded structures, the anionic structure-directing agents (e.g., organocarboxylates) render well-defined metal-carboxylate coordination motifs in extended architectures spanning from low-dimensional (0D, 1D) to high-dimensional cationic inorganic Pb-X-Pb (X = F-/Cl-/Br-/I-) sublattices. This family of organolead halide coordination polymers can endure chemically reactive environments over a wide range of pH and aqueous boiling condition, which have been systematically investigated by experimental studies and theoretical calculations. Many chloride/bromide-based coordination polymers show air-stable, broadband self-trapped emission with large Stokes shift and high color rendition, exhibiting the absolute quantum yields of 35-72%. Among them, the porous frameworks with low-dimensional (0D, 1D) inorganic blocks are recognized as a rare class of porous metal-organic frameworks (MOFs) constructed by lead halides as secondary building units (SBUs). They not only occupy substantially higher light-harvesting and carrier-transport properties than conventional metal oxide-based MOFs, but also allow for isoreticular modification to regulate the PL characteristics by guest molecules. More importantly, combining the high stability with excellent carrier characteristics, a layered organolead iodide coordination polymer shows the overall photocatalytic water splitting without the use of any sacrificial agent under simulated sunlight illumination. Given the wide choice of structurally diverse organocarboxylate linkers, we hope this Account provides deep insights on the importance of coordination chemistry in the discovery of a wide family of intrinsically stable organolead halides to expand their photophysical applications.

Recent Progress on Boosting the Perovskite Film Quality of All-Inorganic Perovskite Solar Cells

All-inorganic CsPbX3 perovskite material not only has the benefits of advanced light absorption coefficient, long carrier lifetime, and simple preparation process of organic–inorganic perovskite materials but it also maintains excellent stability under the erosion of damp heat. Stability is the premise of its industrialization, so all-inorganic perovskite is undoubtedly a very competitive direction for the development of perovskite materials. However, there are still many defects in the all-inorganic perovskite thin films, and it is difficult to obtain high power conversion efficiency (PCE). This review systematically summarizes additive engineering, solvent engineering, and interface engineering methods to promote the thin film property for a high PCE in recent years.

Metal halide HgI2 monolayer with auxetic property and photocatalysis application

Recently, two-dimensional (2D) metal halides have shown extraordinary performances as photocatalysts, triggering our enormous interest to explore new 2D metal halides for photocatalysis water splitting. Here, based on an unbiased first-principles swarm intelligence structure search, we identified a thermally and dynamically stable HgI2 monolayer. Interestingly, its atomic configuration forms an unusual in-plane negative Poisson's ratio, resulting in an auxetic property. More importantly, the HgI2 monolayer exhibits excellent optoelectronic properties, including suitable direct bandgap (∼2.45 eV), good carrier mobility (×102 cm2 V−1 s−1), excellent light absorption coefficient (×105 cm−1), and suitable band edges for photocatalytic water splitting. These excellent characteristics make the HgI2 monolayer fulfill the basic criteria of efficient photocatalysts for water splitting, supporting it as a promising candidate for photocatalytic materials. Our findings bloom the 2D metal halides family and offer a new candidate material for photocatalysis water splitting.

Direct Z-scheme GaSe/ZrS2 heterojunction for overall water splitting

In this paper, a novel GaSe/ZrS2 heterojunction is designed and systematically studied. The monolayers in this heterojunction can be easily fabricated and the heterojunction has good stability. More importantly, electronic structures, band alignment, differential charge density and the built-in electric field show that it is a direct Z-scheme photocatalyst that can not only effectively separate photogenerated carriers but also improve the redox ability of carriers. The mobility of the electrons in this heterostructure is as large as 1450.38 cm2V−1s−1 (same magnitude order of black phosphorene) along the zigzag direction, which is beneficial to photocatalytic performance. The band alignment shows that GaSe/ZrS2 is suitable for overall water splitting and the splitting can happen spontaneously. Moreover, GaSe/ZrS2 heterojunction has excellent absorption coefficients (higher than 105cm−1) in both visible and ultraviolet ranges which is very beneficial to photocatalytic overall water splitting. The study of electric field and biaxial strain effects on GaSe/ZrS2 heterojunction show that the light absorption coefficients of GaSe/ZrS2 heterojunction can be obviously further improved by applying biaxial strain. Our work shows that GaSe/ZrS2 heterojunction is a promising photocatalysts for overall water splitting.

Remarkable Stability and Optoelectronic Properties of an All-Inorganic CsSn0.5Ge0.5I3 Perovskite Solar Cell

Sn-Ge mixed perovskites have been proposed as promising lead-free candidates in the photovoltaics (PV) field. In this work, we discovered a stable P1 phase Sn-Ge mixed structure (CsSn0.5Ge0.5I3) with an appropriate band gap value of 1.19 eV, which manifests its unique structural stability and physics properties. The thermodynamic stability of this mixed structure under different growth conditions and all possible native defects are depicted in detail. The formation energies and dominant native point defects indicate that P1 phase CsSn0.5Ge0.5I3 exhibits unipolar self-doping behavior (p-type conductivity) and good defect tolerance while the growth condition changes. In addition, the calculation of light absorption confirmed that the P1 phase has a higher light absorption coefficient than that of MAPbI3 in the visible light range, showing excellent light absorption. Our work not only provides theoretical guidance for unraveling the unusual structural stability of Sn-Ge mixed perovskites, but also offers a useful scheme to modulate the stability and optoelectronic properties of Ge-based perovskites through alloy engineering.

Tunable electronic and photodiode characteristics of Janus WSeTe: A first-principles study

Janus transition metal chalcogenides have captured the wide attention due to the asymmetric facial properties. Using the first principles calculations in combination with the nonequilibrium Green's function method, we studied the electronic structure, transport and optical properties of WSeTe monolayer. The results show that the electronic properties of WSeTe monolayer can be effectively regulated by biaxial strain and electric field. To be specific, a phase transition from semiconductor to metal accompanied with direct to indirect gap transition can be achieved by applying the biaxial strain. Besides, the optical properties of WSeTe monolayer can also be significant improved in the visible light region with a red and blue shift of optical absorption peaks under the tensile and compressive strain respectively. For devices based on WSeTe monolayer, the current switching ratios are up to 1010, which represent a perfect diode behavior can be observed in the case of ±12% strain. Furthermore, for pin-junction based on WSeTe monolayer, a considerable photocurrents which can be obtained from the light absorption coefficients located in the scope of 1∼3 eV, mean a strong photoelectronic response to the red and orange light region. The results show great potential for the application of WSeTe monolayer in switching and photoelectric devices.

Impacts of springtime biomass burning in Southeast Asia on atmospheric carbonaceous components over the Beibu Gulf in China: Insights from aircraft observations.

Limited by the scarcity of in situ vertical observation data, the influences of biomass burning in Southeast Asia on major atmospheric carbonaceous compositions in downwind regions have not been thoroughly studied. In this study, aircraft observations were performed to obtain high time-resolved in situ vertical distributions of black carbon (BC) as well as carbon monoxide (CO) and carbon dioxide (CO2). Four types of profiles were revealed: Mode I (from 2000 to 3000 m, the BC, CO and CO2 concentrations were enhanced), Mode II (with increasing altitude, the BC, CO and CO2 concentrations almost decreased), Mode III (inhomogeneous vertical BC, CO and CO2 profiles with BC peaks were observed from 2500 to 3000 m) and Mode IV (the BC, CO and CO2 concentrations increased above 1500 m). Furthermore, simulations were conducted to calculate radiative forcing (RF) caused by BC and study the heating rate (HR) of BC in combination with the vertical BC profiles. A larger BC distribution in the atmosphere resulted in a sharp RF change from negative to positive values, imposing a nonnegligible influence on the atmospheric temperature profile, with maximum HR values ranging from 0.4 to 5.8 K/day. The values of the absorption Ångström exponent (AAE) were 1.46 ± 0.11 and 1.48 ± 0.17 at altitudes from 1000 to 2000 and 2000-3000 m, respectively. The average BC light absorption coefficient at the 370 nm wavelength (α BC (370)) accounted for 50.3 %-76.8 % of the α (370), while the brown carbon (BrC) light absorption coefficient at the 370 nm wavelength (α BrC (370)) contributed 23.2 %-49.7 % to the α (370) at altitudes of 1000-2000 m. At altitudes of 2000-3000 m, α BC (370) and α BrC (370) contributed 43.8 %-88.2 % and 11.8 %-56.2 % to the α (370), respectively. These findings show that calculations that consider the surface BC concentration but ignore the vertical BC distribution could result in massive uncertainties in estimating the RF and HR caused by BC. This study helped achieve a deeper understanding of the influences of biomass burning over the region of Southeast Asia on the profiles of atmospheric carbonaceous compositions and atmospheric BC absorption and its warming effect.

Two Janus Ga2STe monolayers and their electronic, optical, and photocatalytic properties.

Recently, two-dimensional Janus materials have attracted increasing interest due to their unique structure and novel properties. Based on density-functional and many-body perturbation theories (i.e. DFT + G0W0 + BSE methods), the electronic, optical, and photocatalytic properties of Janus Ga2STe monolayers with two configurations are explored systematically. It is found that the two Janus Ga2STe monolayers exhibit high dynamical and thermal stabilities and have desirable direct gaps of about 2 eV at the G0W0 level. Their optical absorption spectra are dominated by the enhanced excitonic effects, in which bright bound excitons possess moderate binding energies of about 0.6 eV. Most interestingly, Janus Ga2STe monolayers show high light absorption coefficients (larger than 106 cm-1) in the visible light region, effective spatial separation of photoexcited carriers, and suitable band edge positions, which make them potential candidates for photoelectronic and photocatalytic devices. These observed findings enrich the deep understanding of the properties of Janus Ga2STe monolayers.

Zero-bias Bi-based perovskite image sensor arrays with direct laser-scribing process

We presented a 25 × 25 array imaging sensor based on Cs3Bi2Br9 photodetectors using a laser-scribing technique, which has the advantages of low cost, high accuracy, and being lithography-free.

A photo-switchable rectifier based on the MAPbBr3–MAPbCl3 halide perovskite heterostructure for dual-wavelength optical communications

A MAPbBr3–MAPbCl3 halide perovskite heterostructure enables photo-switchable rectification.

Theoretical exploration of the structural, electronic and optical properties of g-C3N4/C3N heterostructures.

Integration of graphene-like carbon nitride materials is essential for nanoelectronic applications. Using density-functional theory (DFT), we systematically investigate the structural, electronic and optical properties of a s-triazine-based g-C3N4/C3N heterostructure under different modified conditions. The g-C3N4/C3N van der Waals heterostructure (vdWH) formed has an indirect bandgap with type-II band alignment and the band structures can be tuned from type-II band alignment to type-I band alignment by applying biaxial strains and external electric fields (Efield). Compared to single transition metal (TM) atoms at g-C3N4/C3N surfaces, the TM atoms anchored in the interlayer region exhibit more stability, and the corresponding bandgaps are changed from 0.19 eV to 0.61 eV. In addition, the g-C3N4/C3N heterostructure has a strong absorption coefficient in the ultraviolet-visible light region along the x direction. It is found that compressive strain has a large influence on the absorption coefficient of the g-C3N4/C3N system. With the increased compressive strain, the absorption spectra in the visible light region disappeared. Tensile strain has a slight effect on the absorption range, but causes a red shift of the absorption spectrum. In comparison, the light absorption coefficient of the g-C3N4/C3N system remains almost unchanged under the Efield conditions. In summary, the formation of a s-triazine-based g-C3N4/C3N heterostructure has shown potential for applications in nanoelectronic and optoelectronic devices.

A semiconductor Sc2S3 monolayer with ultrahigh carrier mobility for UV blocking filter application.

For humans, ultraviolet (UV) light from sun is harmful to our eyes and eye-related cells. This detrimental fact requires scientists to search for a material that can efficiently absorb UV light while allowing lossless transmission of visible light. Using an unbiased first-principles swarm intelligence structure search, we explored two-dimensional (2D) Sc-S crystals and identified a novel Sc2S3 monolayer with good thermal and dynamical stability. The optoelectronic property simulations revealed that the Sc2S3 monolayer has a wide indirect bandgap (3.05 eV) and possesses an ultrahigh carrier mobility (2.8 × 103 cm2 V-1 s-1). Remarkably, it has almost transparent visible light absorption, while it exhibits an ultrahigh absorption coefficient up to × 105 cm-1 in the ultraviolet region. Via the application of biaxial strain and thickness modulation, the UV light absorption coefficients of Sc2S3 can be further improved. These findings manifest an attractive UV blocking optoelectronic characteristic of the Sc2S3 configuration as a prototypical nanomaterial for the potential application in UV blocking filters.

Construction of a MAPbBr3/BiFeO3 Z-scheme heterojunction with enhanced piezo-photocatalytic performance

Based on the large visible light absorption coefficient and tunable band gap of MAPbBr3, weakening the strong photogenerated carrier recombination tendency to exploit the CO2 reduction potential is a worthy research topic.

Switch effect on controlled water splitting by biaxial strain regulating the promising two-dimensional Janus X2PAs (X = Si, Ge and Sn) photocatalyst.

Two-dimensional photocatalytic materials with unique properties have been well-reported in recent decades. However, strategies for controlling the photocatalytic process are still ongoing. Herein, Janus X2PAs (X = Si, Ge and Sn) monolayers have been explored by first-principles calculations to meet this challenge. All strain-free X2PAs monolayers exhibit excellent photocatalytic properties with high carrier mobility (2.39 × 102-1.34 × 104 cm2 V-1 s-1), suitable band edge positions straddling the standard redox potential of water and large visible light absorption coefficients (up to 105 cm-1). Most importantly, a reaction switch effect is proposed for the first time towards controlling the microscopic photocatalytic process of water splitting on X2PAs monolayers through macroscopic mechanical strain. This effect renders the Janus X2PAs photocatalytic switches among the states of only oxygen evolution reaction, only hydrogen evolution reaction and the full redox reaction for controlled water splitting. This work not only provides a new avenue for designing highly tunable photocatalysts but also offers new physical insights into controlling the photocatalytic water-splitting reaction.

Влияние катамина АБ на комплексообразование бромпирогаллолового красного с ионами скандия

The regularities of complexation of bromopyrogallol red with scandium ions in the dual system and in the presence of cationic surfactant catamin AB have been studied. The optimum pH interval of complexation was determined. The light absorption spectra of the dye and its complexes with scandium ions in dual systems and in the catamin AB presence at different pH values and surfactant concentrations were recorded. The ratio between metal ion and reagent in complexes without and in the presence of catamin AB was determined by saturation and isomolar series methods at pH 5,90 and 6,40. The conditional stability constants of the obtained complexes were determined by the Babko method, calibration graphs were constructed, and molar light absorption coefficients were calculated. The influence of interfering ions was studied at pH 6,40.

Изучение реакции ионов Cu(II) с N-(бензоил)-N'-(фенилсульфонил)гидразином в аммиачных средах спектрофотометрическим методом

The reaction of complexation of N-(benzoyl)-N'-(phenylsulfonyl)hydrazine with Cu(II) ions in an ammonia medium has been studied. The absorption spectra of the reagent and its complex with Cu(II) ions have been recorded and analyzed. The optimal conditions for the formation of the complex compound were found: the pH range of complex formation; optimal time for color development; amount of photometric reagent. Under optimal conditions for the complex formation of BPSH with Cu(II) ions, a calibration graph was constructed. The Bouguer-Lambert-Beer law is fulfilled in the range from 0,5 to 1,75 mg Cu(II) in 25 ml of solution. The true (19389) and apparent (4708) molar light absorption coefficients were calculated. The methods of saturation, equilibrium shift, curve intersection, isomolar series, and conductometric titration were used to determine the molar ratios in a solution of a complex compound – [Сu(II)]:[BFSH] = 1:1 and 1:2. According to the Babko method, the conditional stability constant of the complex was calculated – 2,45∙1013. The convergence and correctness of the spectrophotometric technique were determined by the method of mathematical statistics.

Intrinsic defects at the interface of the FAPbI3/MAPbI3 superlattice: insight from first-principles calculations.

The use of a superlattice structure is an effective strategy to develop novel perovskites and obtain excellent light-absorbing materials. Based on first-principles calculations, we systematically studied the properties of intrinsic point defects at the interface of the FAPbI3/MAPbI3 superlattice. Our calculations show that charged defects are easier to form as compared to neutral ones at the superlattice interface due to low formation energies. Most defects with low formation energies have a shallow level in the band gap, and some deep level defects have high formation energies, so the superlattice perovskite exhibits high defect tolerance. PbI3+ is a dominant and detrimental defect, which acts as a non-radiative recombination center because it has low formation energy and a deep transition level. To avoid the generation of PbI3+ defects, it is suggested to synthesize FAPbI3/MAPbI3 superlattices under I-rich conditions. The calculated light absorption coefficients and photovoltaic performance parameters demonstrate that the presence of defects leads to a certain degree of reduction in light absorption and power conversion efficiency (PCE) of solar cells made of FAPbI3/MAPbI3 superlattices, but the excellent performance of the perovskite solar cell (PSC) is basically retained. The superlattice perovskites are still promising candidates for light-absorbing materials of PSCs. This study is expected to contribute to a better understanding of the properties of defects at the superlattice interface and provide theoretical support for the design of high performance PSCs.

Highly-efficient heterojunction solar cells based on 2D Janus transition-metal nitride halide (TNH) monolayers with ultrahigh carrier mobility.

Symmetry breaking has a crucial effect on electronic band structure and subsequently affects the light-absorption coefficient of monolayers. We systematically report a family of two-dimensional (2D) Janus transition-metal nitride halides (TNHs, T = Ti, Zr, Hf, Fe, Pd, Pt, Os, and Re; H = Cl and F) with breaking of both in-plane and out-of-plane structural symmetry. The dynamical, thermal and mechanical stabilities are calculated to check the stability of the Janus TNHs. The electric properties of ten TNHs are studied via the HSE06+SOC method and the band gaps range from 0.93 eV (PdNCl) to 4.74 eV (HfNCl). Desirable light adsorption coefficients of up to 105 cm-1 are obtained for the Janus TNHs with no central symmetry. The Janus OsNCl monolayer shows excellent electrical transport properties and ultrahigh carrier mobility (104 cm2 V-1 s-1). Heterojunctions formed by stacking two Janus TNH monolayers are further investigated for solar cell applications. Eight of the heterojunctions have type-II band alignments. Surprisingly, the OsNCl/FeNCl heterojunction has a power conversion efficiency (PCE) of 23.45%, which is a larger value compared to the PCE of GeSe/SnSe heterostructures (21.47%). The optical properties and the built-in electric field of the OsNCl/FeNCl heterojunction are investigated. These results indicate that the stable Janus TNH monolayers have potential applications in photoelectric devices, and the vertical heterojunctions can be used in solar cells.

Calculation of tunable electronic and optical properties of AlSb/CdSe heterojunction based on first principles

The geometric structure, electronic and optical peculiarities of AlSb/CdSe heterojunction were investigated based on the first principles computation of Density Functional Theory (DFT). It is detected that the A1-type AlSb/CdSe heterojunction with a layer spacing of 3.218 Å has the most stabilized structure. The heterojunction has a smaller band gap than two monolayers, which facilitates the excitation of photogenerated electrons. The heterojunction also pertains to Type-Ⅱ heterojunction, which is helpful for the separation of photogenerated electrons and hole pairs. A1-type AlSb/CdSe heterojunction also has higher Ultraviolet light (UV) absorption coefficient, which has good application value in the field of UV detectors. By applying electrical field and stress to AlSb/CdSe heterojunction, it is spotted that can efficaciously modulate the band gap of heterojunction, the orientation and amount of electron transfer, and make heterojunction transform from Type-Ⅱ to Type-Ⅰ, so that the heterojunction can not only be applied in the field of the photoelectric detector but also be used in laser and other fields. The applied electrical field and stress can rise the optical absorption coefficient of the heterojunction, and make the absorption spectrum of the heterojunction appear blue or red shift, which can adjust the optical peculiarities of the heterojunction.

Molecular characteristics and compositions affecting light absorption features of cloud water revealed by Fourier transform ion cyclotron resonance mass spectrometry

In-cloud brown carbon (BrC) can change cloud lifetimes and radiative effects. However, little is known regarding its molecular-level composition. Herein, the molecular characteristics of water-soluble organic matter (WSOM) in cloud water were analyzed by Fourier transform ion cyclotron resonance mass spectrometry coupled with electrospray ionization (ESI) in negative mode. CHON formulas were dominant in WSOM and exhibited the highest level of aromaticity. Combined with the water-soluble BrC (WS-BrC) light-absorption coefficient (Abs365), the principal component analysis indicated that WS-BrC light absorption was mainly affected by unsaturation, aromaticity, highly oxygenated compounds, and N-containing formulas. Thirteen important potential WS-BrC were identified based on a random forest regression model, which could explain 61.7% of the variation in Abs365. Among them, C7H6N2O5, C8H8N2O5, C9H10N2O5, C10H12N2O5, C8H10O5S, and C8H9NO7S were identified as WS-BrC for the first time in clouds, and these may belong to dinitrophenols or nitrotyrosine, organosulfates, and their derivatives. These findings would improve our understanding of cloud WS-BrC composition.