Recombination Energy Research Articles

Influence of Intermolecular Interactions on the Photophysical Properties of Carbazolyl Phosphorescent Molecules

AbstractThe photophysical properties of three carbazolyl phosphorescent molecules with similar structures‐5‐(9H‐carbazole‐9‐group) nicotinitrile (P35N), 5‐(9H‐carbazole‐9‐group) nicotinamide (P35M) and 2‐(9H‐carbazole‐9‐group) isonicotinamide (P25M)‐are investigated theoretically. The influence on luminescence is primarily elucidated through an analysis of geometry, electronic structure, and the dynamic processes occurring within the excited state. Structural analysis indicates that P35M exhibits the most effective luminescence due to minimal structural changes, reduced separation between the electron and hole, and enhanced intermolecular interactions within the crystal. Excited state dynamics and recombination energy analysis indicate that the higher triplet exciton population in the P35M molecule contributes to its long‐lived phosphorescence. Furthermore, the intersystem crossing process for the three molecules is predominantly governed by low‐frequency torsional rotation, while bond stretching vibrations are the primary factor leading to the inactivation of non‐radiative processes. The distinct vibrational channels associated with reverse intersystem crossing and non‐radiative processes present opportunities for further enhancement of the phosphorescent characteristics of these molecules.

Oxygen Vacancies Regulated S-Scheme Charge Transport Route in BiVO4-OVs/g-C3N4 Heterojunction for Enhanced Photocatalytic Performance.

Oxygen vacancies (OVs) are widely considered as active sites in photocatalytic reactions, yet the crucial role of OVs in S-scheme heterojunction photocatalysts requires deeper understanding. In this work, OVs at hetero-interface regulated S-scheme BiVO4-OVs/g-C3N4 photocatalysts are constructed. The Fermi-level structures of BiVO4 and g-C3N4 lead to a redistribution of charges at the heterojunction interface, inducing an internal electric field at the interface, which tends to promote the recombination of photogenerated carriers at the interface. Importantly, the introduction of OVs induces defect electronic states in the BiVO4 bandgap, creating indirect recombination energy level that serves as crucial intermediator for photogenerated carrier recombination in the S-scheme heterojunction. As a result, the photocatalytic degradation rate on Rhodamine B (RhB) and tetracyclines (TCs) for the optimal sample is 10.7 and 11.8 times higher than the bare one, the photocatalytic hydrogen production rate is also improved to 558 µmol g-1 h-1. This work shows the importance of OVs in heterostructure photocatalysis from both thermodynamic and kinetic aspects and may provide new insight into the rational design of S-scheme photocatalysts.

CHIANTI—An Atomic Database for Emission Lines—Paper. XVIII. Version 11, Advanced Ionization Equilibrium Models: Density and Charge Transfer Effects

Version 11 of the chianti database and software package is presented. Advanced ionization equilibrium models have been added for low charge states of seven elements (C, N, O, Ne, Mg, Si, and S), and represent a significant improvement especially when modeling the solar transition region. The models include the effects of higher electron density and charge transfer on ionization and recombination rates. As an illustration of the difference these models make, a synthetic spectrum is calculated for an electron pressure of 7 × 1015 cm−3 K and compared with an active region observation from HRTS. Increases are seen in factors of 2–5 in the predicted radiances of the strongest lines in the UV from Si iv, C iv, and N v, compared to the previous modeling using the coronal approximation. Much better agreement (within 20%) with the observations is found for the majority of the lines. The new atomic models better equip both those who are studying the transition region and those who are interpreting the emission from higher-density astrophysical and laboratory plasma. In addition to the advanced models, several ion data sets have been added or updated, and data for the radiative recombination energy loss rate have been updated.

Air-Processed Efficient Cesium-Based Two-Dimensional Perovskite Solar Cells Based on Asymmetric Chiral Ammonium Salts.

Cesium-based two-dimensional (2D) perovskites with attractive phase and environmental stability have broad application prospects in single-junction and tandem perovskite solar cells (PSCs). However, the severe nonradiative recombination and significant energy losses due to disordered phase orientations and phase distributions greatly hinder the carrier transport performance of cesium-based 2D PSCs and severely limit their photovoltaic performance. Here, we employ an asymmetric chiral spacer cation source, (R)-α-phenylethylamine acrylate (R-α-PEAAA), to prepare high-quality 2D cesium-based films with uniform phase distribution and high out-of-plane orientation by air processing, resulting in efficient carrier transport. More importantly, the asymmetric chiral spacer R-α-PEA has a stronger dipole moment than its isomer (PEA), which can regulate the dielectric properties of cesium-based 2D perovskites and promote charge dissociation. In addition, the chiral R-α-PEA can optimize the morphology and out-of-plane orientation of perovskite films, reduce trap density and nonradiative recombination loss, and optimize energy level alignment, thus enhancing carrier transport. As a result, cesium-based 2D PSCs (R-α-PEA2Cs4Pb5I16, n = 5) achieved a record power conversion efficiency of 19.71% and the unencapsulated device maintained over 90% efficiency after 1500 h of continuous light exposure and ambient storage (35 ± 5% relative humidity). This study provides an idea for the development of chiral 2D perovskite with efficient charge carrier transport toward efficient and stable cesium-based 2D PSCs.

Recent Progress on Cross-Linkable Fullerene-Based Electron Transport Materials for Perovskite Solar Cells.

Fullerene-based derivatives are frequently used as electron transport materials (ETMs) and interface buffers for perovskite solar cells (PSCs) due to their excellent properties, including high electron affinity and mobility, low recombination energy, tunable energy levels, and solution processability. However, significant challenges arise because fullerene derivatives tend to aggregate and dimerize, which reduces exciton dissociation and charge transport capacity. Additionally, their chemical compatibility with perovskite absorbers facilitates halide diffusion and degradation of PSCs. This overlap causes delamination and dissolution during device fabrication, hindering the performance enhancement of fullerene-based PSCs. To address these issues, researchers have developed cross-linkable fullerene materials. These materials have been shown to not only significantly improve the power conversion efficiency (PCE) of PSCs but also effectively enhance the device stability. In this review, we summarized recent research progress on cross-linkable fullerene derivatives as ETMs for PSCs. We systematically analyze the impact of these cross-linked ETMs on device performance and long-term stability, focusing on their molecular structures and working mechanisms. Finally, we discuss the future challenges that need to be overcome to advance the application of cross-linkable fullerene materials in PSCs.

Investigating novel perovskites of lead-free flexible solar cell CH3NH3BiI3 and their photovoltaic performance with efficiency over 26%

Perovskite solar cells are increasing attention due to their unique characteristics in the field of photovoltaic technology. Lead-based perovskite solar cells are particularly notable for their high efficiency. However, their commercial production is limited because of the use of lead-based absorbers. As a result, research has shifted towards exploring lead-free alternatives in the realm of perovskite materials. This study utilizes SCAPS-1D simulation software to optimize the performance of a lead-free flexible solar cell. Lead (Pb), a group 14 element, is proposed to be replaced by bismuth (Bi), a group 15 element. We investigate how the selection of configurations for the Electron Transport Layer (ETL), Hole Transport Layer (HTL), and absorber layer impacts solar cell performance. This study represents a comprehensive examination of this material. The device optimization involves using a fluorine-doped tin oxide (FTO) substrate, cadmium sulfide (CdS), tungsten disulfide (WS2), titanium dioxide (TiO2), and fullerene (C60) as ETL components, methyl ammonium bismuth iodide (CH3NH3BiI3) as the absorber, molybdenum disulfide (MoS2) as the HTL, and platinum (Pt) as the electrode. In addition to optimizing ETL and HTL configurations, this study explores the effects of various factors such as absorber, ETL, and HTL thickness, shunt and series resistance, temperature variations, Mott-Schottky behavior, capacitance, recombination, generation rates, J-V characteristics, and quantum energy. The results show that the solar cell configuration using FTO/CdS/CH3NH3BiI3/MoS2/Pt achieves an efficiency of 26.60 %, a current density (JSC) of 32.02 mA/cm2, an open circuit voltage (VOC) of 0.974 V, and a fill factor (FF) of 85.24 %. This represents a significant improvement compared to previous research. This detailed simulation analysis enables researchers to develop cost-effective and highly efficient perovskite solar cells (PSCs), driving advancements in solar technology.

Dust formation in common envelope binary interactions – II: 3D simulations with self-consistent dust formation

ABSTRACT We performed numerical simulations of the common envelope (CE) interaction between thermally pulsing asymptotic giant branch (AGB) stars of 1.7 and 3.7 M$_{\odot }$, respectively, and a 0.6 M$_{\odot }$ compact companion. We use tabulated equations of state to take into account recombination energy. For the first time, formation and growth of dust is calculated explicitly, using a carbon dust nucleation network with a C/O abundance ratio of 2.5 (by number). The first dust grains appear within $\sim$1–3 yr after the onset of the CE, forming an optically thick shell at $\sim$10–20 au, growing in thickness and radius to values of $\sim$400–500 au over $\sim$40 yr, with temperatures around 400 K. Most dust is formed in unbound material, having little effect on mass ejection or orbital evolution. By the end of the simulations, the total dust yield is $\sim 8.4\times 10^{-3}$ and $\sim 2.2\times 10^{-2}$ M$_{\odot }$ for the CE with a 1.7 and a 3.7 M$_{\odot }$ AGB star, respectively, corresponding to a nucleation efficiency close to 100 per cent, if no dust destruction mechanism is considered. Despite comparable dust yields to single AGB stars, in CE ejections the dust forms a thousand times faster, over tens of years as opposed to tens of thousands of years. This rapid dust formation may account for the shift in the infrared of the spectral energy distribution of some optical transients known as luminous red novae. Simulated dusty CEs support the idea that extreme carbon stars and ‘water fountains’ may be objects observed after a CE event.

Reduction of c-type cytochromes by Fe(II)-ligand under oxic conditions: Roles of Fe(II)-heme complexation and reactive oxygen species

Microbial Fe(II) oxidation is mainly mediated by the outer-membrane proteins that contain c-type cytochromes (c-Cyts), and the widespread Fe(II)-oxidizing bacteria are usually subjected to fluctuations between oxic and anoxic conditions. However, it remains unclear how oxygen affects the redox dynamics of c-Cyts by Fe(II), particularly in the presence of organic ligands that are widely distributed in the environment. Here, the reduction of a model heme-containing c-Cyts by Fe(II) was investigated in the absence and presence of organic ligands (i.e., citrate and acetate) at pH 5.5 under anoxic and oxic conditions. The kinetic results showed that c-Cyts reduction was enhanced by citrate and acetate under anoxic conditions, and the enhancement by citrate was more pronounced than that by acetate. The speciation calculation and cyclic voltammetry results suggested that the proportions of Fe(II)-Citrate complexes were much higher than those of Fe(II)-Acetate complex, but the addition of acetate and citrate caused minor changes in redox potential of Fe(II)/Fe(III) species. Further analysis using quantum chemical computation demonstrated that the formation of Fe(II)-Heme complexes via lateral binding to the carboxyl group of c-Cyts was more stable than those via replacing the S-linked axial ligand of heme, with the recombination energy with Heme ranking as Fe(II)-Citrate < Fe(II)-Acetate < Fe(II). Therefore, the stronger complexation of Fe(II)-Citrate and its lower recombination energy with c-Cyts drive the enhanced c-Cyts reduction under anoxic conditions. By contrast, the c-Cyts reduction by Fe(II) and Fe(II)-ligand was inhibited under oxic conditions. The electron spin resonance characterization indicated that both O2−• and OH• radicals were produced in the system of c-Cyts with Fe(II) or Fe(II)-ligand under oxic conditions and the signals were higher with Fe(II)-ligand than those with Fe(II). These reactive oxygen species were proposed to enable a re-oxidation of the c-Cyts that was reduced by Fe(II) or Fe(II)-ligand, causing an inhibitory effect on the observed c-Cyts reduction and forming more reactive oxygen species. Our findings shed light on the important roles of Fe(II)-ligand-heme complexation and reactive oxygen species in the interaction between Fe(II) and c-Cyts, which deepen the understanding of microbial/enzymatic Fe(II) oxidation under oxic conditions at the molecular level.

Formation of long-period post-common-envelope binaries

Context. The vast majority of close binaries containing a compact object, including the progenitors of supernovae Ia and at least a substantial fraction of all accreting black holes in the Galaxy, form through common-envelope (CE) evolution. Despite this importance, we struggle to even understand the energy budget of CE evolution. For decades, observed long-period post-CE binaries have been interpreted as evidence of additional energies contributing during CE evolution. We have recently shown that this argument is based on simplified assumptions for all long-period post-CE binaries containing massive white dwarfs (WDs). The only remaining post-CE binary star that has been claimed to require contributions from additional energy sources to understand its formation is KOI 3278. Aims. Here, we address in detail the potential evolutionary history of KOI 3278. In particular, we investigate whether extra energy sources, such as recombination energy, are indeed required to explain its existence. Methods. We used the 1D stellar evolution code MESA to carry out binary evolution simulations and searched for potential formation pathways for KOI 3278 that are able to explain its observed properties. Results. We find that KOI 3278 can be explained if the WD progenitor filled its Roche lobe during a helium shell flash. In this case, the orbital period of KOI 3278 can be reproduced if the CE binding energy is calculated taking into account gravitational energy and thermodynamic internal energy. While the CE evolution that led to the formation of KOI 3278 must have been efficient – that is, most of the available orbital energy must have been used to unbind the CE – recombination energy is not required. Conclusions. We conclude that currently not a single observed post-CE binary requires one to assume that energy sources other than gravitational and thermodynamic energy are contributing to CE evolution. KOI 3278, however, remains an intriguing post-CE binary as, unlike its siblings, understanding its existence requires highly efficient CE ejection.

Threshold displacement energy map of Frenkel pair generation in [formula omitted]-Ga2O3 from machine-learning-driven molecular dynamics simulations

β-gallium oxide (β-Ga2O3) shows great promise for electronics applications, particularly, in future space operating devices exposed to harsh radiation environments for extended times. This study focuses on crucial, yet not fully explored, aspects of radiation damage in this material, such as threshold displacement energies and formation of various radiation-induced Frenkel pairs. Analyzing over 5,000 molecular dynamics simulations based on our machine-learning potentials, we conclude that the threshold displacement energies for two Ga sites, the tetrahedral (22.9 eV) and octahedral (20 eV) ones, differ stronger than the same values for three different O sites, which range only between 17 eV and 17.4 eV. Mapping of threshold displacement energies unveils significant differences in displacements for all five atomic sites. Our newly developed defect identification methodology successfully classified multiple Frenkel pair types in β-Ga2O3, with over ten different Ga and two primary O ones with a predominant O split interstitial at the O1 site. Finally, the calculated recombination energy barriers suggest that O Frenkel pairs are more likely to recombine upon annealing than Ga. These insights are pivotal for understanding the radiation damage and defect formation in Ga2O3, providing the basis for design of Ga2O3-based electronics with high radiation resistance.

Regulating the perovskite/C60 interface via a bifunctional interlayer for efficient inverted perovskite solar cells

Inverted perovskite solar cells are promising candidates in photovoltaic fields due to their low-temperature processing, simplified fabrication, and enhanced stability when compared with the conventional configuration. However, the significant non-radiative recombination losses and energy alignment mismatch at the perovskite/C60 interface limit the device's performance and long-term stability. To overcome this drawback, we introduced trifluoromethoxy-functionalized phenethylammonium iodide salts with high polarity between the perovskite and C60 electron transporting layer. This bifunctional interlayer not only effectively passivates the perovskite surface and interface but also reduces the minority carriers through the band rearrangement at this interface, thus significantly suppressing the deteriorating interfacial non-radiative recombination. The modified interlayer also facilitates electron extraction by reducing the offset between the perovskite and C60, contributing to an improved photocurrent and fill factor. The resultant inverted perovskite solar cell based on a Cs0.05FA0.85MA0.10Pb(I0.95Br0.05)3 composition reveals a power conversion efficiency of 24.7 % at the reverse scan and shows negligible efficiency loss after 600 h of maximum power point tracking under one-sun illumination. Overall, this feasible deposition of ammonium-based interlayer establishes a successful demonstration of efficient and stable inverted devices to accelerate the commercialization of perovskite photovoltaics.

Spatially correlated stress-photoluminescence evolution in GaN/AlN multi-quantum wells

In the manufacture of semiconductor devices, cracking of heterostructures has been recognized as a major obstacle for their post-growth processing. In this work, we explore cracked GaN/AlN multi-quantum wells (MQWs) to study the influence of pressure on the recombination energy of the photoluminescence (PL) from the polar GaN QWs. We grow GaN/AlN MQWs on a GaN(0001)/sapphire template, which provides 2.4% tensile strain for epitaxial AlN. This strain relaxes through the generation and propagation of cracks, resulting in a final inhomogeneous distribution of stress throughout the film. The crack-induced strain variation investigated by micro-Raman spectroscopy and X-ray diffraction mapping revealed a correlation between the spacing of the cracks and the amount of strain between them. We have developed a 2D model that allows us to calculate the spatial variation of the in-plane strain in the GaN and AlN layers. The measured values of compressive in-plane strain in the GaN QWs vary from -0.4 % away from cracks, to -0.7 % near cracks. PL from the GaN QWs exhibits a clear correlation to the varying strain resulting in an energy shift of ∼ 140 meV. As a result, we can experimentally calculate a pressure coefficient of PL energy of ∼ -60.4 meV/GPa for the ∼ 7 nm thick polar GaN QWs. This agrees well with the previously predicted theoretical results by Kaminska et al. in 2016 [DOI: 10.1063/1.4962282], which were demonstrated to break down for such wide QWs. We will discuss this difference with respect to the reduction in both the expected point defects and extended defects resulting from not doping and growth on a GaN template, respectively. As a result, our work indicates that cracks can be utilized for investigating some fundamental material properties related to strain effects.

Efficient Ternary Organic Solar Cells with Suppressed Nonradiative Recombination and Fine-Tuned Morphology via IT-4F as Guest Acceptor.

The large open circuit voltage (VOC) loss is currently one of the main obstacles to achieving efficient organic solar cells (OSCs). In this study, the ternary OSCs comprising PM6:BTP-eC9:IT-4F demonstrate a superior efficiency of 18.2 %. Notably, the utilization of the medium bandgap acceptor IT-4F as the third component results in an exceptionally low nonradiative recombination energy loss of 0.28 V. The desirable energy level cascade is formed among PM6, BTP-eC9, and IT-4F due to the low-lying HOMO and LUMO energy levels of IT-4F. More importantly, the VOC of PM6:BTP-eC9:IT-4F OSCs can reach as high as 0.86 V, which is higher than both binary OSCs without sacrificing JSC and FF. Besides, this strategy proved that IT-4F can not only broaden the absorption range but also work as a morphology modifier in PM6:BTP-eC9:IT-4F OSCs, and there also exists efficient energy transfer between BTP-eC9 and IT-4F. This result provides a promising way to suppress the nonradiative recombination energy loss and realize higher VOC than the two binary OSCs in ternary OSCs to obtain high power conversion efficiencies.

Carbon based cobalt titanate perovskite nanocomposite: Synthesis, characterization, and excellent visible light driven photocatalytic performance

Titanium-based perovskite oxides are the promising photocatalysts for an efficient degradation of organic pollutants. However, charge carriers recombination and wide band gap energy are still the main challenges in their visible-light-driven photocatalytic applications of Titanate perovskites, ATiO3. The immobilization of Titanium-based perovskites on a carbonaceous substrate such as nitrogen-rich carbon nitride, can be considered as an excellent option for enhancing photocatalytic performance. Here, the CoTiO3/C3N5 nanocomposite was synthesized by simple reflux method and used for photocatalytic degradation of three organic pollutants including methylene blue (MB), tetracycline hydrochloride (TC), and bisphenol A (BPA). The results indicated that the photocatalytic activity of the CoTiO3 perovskite was considerably improved by introducing C3N5 nanosheets and fabricating CoTP/C3N5 nanocomposite. The crystalline structure of CoTiO3/C3N5 (CoTP/C3N5) nanocomposites was confirmed successfully by XRD analysis. The specific surface area of the synthesized CoTP/C3N5 nanocomposite was 8.15 m2/g calculated by N2 adsorption–desorption technology. In the 60th minute of the photocatalytic process, the degradation efficiency of MB, TC, and BPA by CoTP/C3N5 were obtained as 98.70, 60.33, and 92.90 %, respectively, which were higher than pristine CoTiO3 nanorods and C3N5 nanosheets. Electrochemical impedance analysis shows that the CoTP/C3N5 nanocomposite has good electrochemical performance. The improvement photocatalytic activity CoTP/C3N5 can be attributed to the suppressing the recombination of photogenerated electrons and holes and good electrochemical performance with high electron transfer capability. The results achieved from UV–Visible Diffused Reflectance Spectroscopy (DRS), mott-schottky measurements and the photocatalytic degradation experiments in the presence of scavengers confirmed the significantly accelerating the Z-scheme charge transfer mechanism where photoexcited carriers can migrate between CoTiO3 perovskite and C3N5 nanosheets.

A comparative study of surface passivation of p-i-n perovskite solar cells by phenethylammonium iodide and 4-fluorophenethylammonium iodide for efficient and practical perovskite solar cells with long-term reliability

Passivation of the defective surface in perovskite absorber layers effectively stabilizes the photovoltaic performance and electronic properties of perovskite solar cells (PSCs). We herein investigated the passivating effects of phenethylammonium iodide (PEAI) and 4-fluorophenethylammonium iodide (F-PEAI) on perovskite absorber layers comparatively, analyzing their impact on morphological, optical, and electrical properties of perovskite absorbers. Both passivation molecules significantly improved film characteristics, with enlarged domain size, uniform surface morphologies, and prolonged carrier lifetime observed in polycrystalline perovskite absorbers. Notably, non-fluorinated PEAI demonstrated superior effectiveness in reducing tail states and defective Pb2+ sites, resulting in more stable absorbers with fewer defects. The passivated perovskite absorbers exhibited higher champion efficiencies (22.07% for PEAI and 20.56% for F-PEAI) compared to control devices (19.53%), attributed to the suppression of interfacial nonradiative recombination and reduction in recombination energy losses. The devices with passivated perovskite absorbers also demonstrated promising indoor photovoltaic performance, achieving an efficiency of 39.04% and 37.02% under dim-light conditions (LED, 6500 K, 1000 Lux), compared to 29.43% in the control device. Importantly, the passivated absorbers maintained 94% of their initial efficiency even after 1250 hours of humidity aging, indicating enhanced hydrophobicity and reduced trap states, resulting in good ambient stability. Our findings highlight the effectiveness of passivation techniques using organic ammonium halide salts in improving the efficiency and stability of perovskite solar cells.

Bridging the Gap between Luminous Red Novae and Common Envelope Evolution: The Role of Recombination Energy and Radiation Force

Luminous red novae and their connection to common envelope evolution (CEE) remain elusive in astrophysics. Here, we present a radiation hydrodynamic model capable of simulating the light curves of material ejected during a CEE. For the first time, the radiation hydrodynamic model incorporates complete recombination physics for hydrogen and helium. The radiation hydrodynamic equations are solved with Guangqi. With time-independent ejecta simulations, we show that the peaks in the light curves are attributed to radiation-dominated ejecta, while the extended plateaus are produced by matter-dominated ejecta. To showcase our model’s capability, we fit the light curve of AT 2019zhd. The central mass object of 6 M ⊙ is assumed based on observations and scaling relations. Our model demonstrates that the ejecta mass of AT 2019zhd falls within the range of 0.04–0.1 M ⊙. Additionally, we demonstrate that recombination energy and radiation force acceleration significantly impact the light curves, whereas dust formation has a limited effect during the peak and plateau phases.

Enabling Low Nonradiative Recombination Losses in Organic Solar Cells by Efficient Exciton Dissociation

AbstractThe achievement of high performance in organic solar cells (OSCs) is highly dependent on efficient exciton dissociation. However, a comprehensive understanding of the exciton dissociation process under photoexcitation in OSCs remains elusive. Herein, a prototypical system of PM6:Y6 is adopted to explore the exciton dissociation process. An organic semiconductor PCz with distinctive photoexcitation signals from PM6 and Y6 is incorporated as the third component. Femtosecond transient absorption spectroscopy demonstrates clear cascade charge transfer processes in ternary PM6:PCz:Y6 system. These cascade channels contribute to enhancing the efficiency of exciton dissociation. Consequently, the nonradiative recombination energy loss is reduced, resulting in an improved power conversion efficiency (PCE) of OSCs. Furthermore, the reduction of energy loss is verified in different OSCs. When PCz is introduced into the D18:L8‐BO system, a low nonradiative recombination energy loss of 0.175 eV is demonstrated, contributing a PCE of over 19%. This work highlights that the insight of efficient exciton dissociation enables low nonradiative recombination losses for efficient OSCs.

Surface Functionalization and Defect Construction of SnO2 with Amine Group for Enhanced Visible‐Light‐Driven Photocatalytic CO2 Reduction

AbstractPhotocatalytic CO2 reduction to hydrocarbon fuels through solar energy provides a feasible channel for reducing CO2 emission and resource depletion. Nevertheless, severe charge recombination and high energy barrier limit the CO2 reduction efficiency. Herein, a surface amine‐functionalized SnO2 with oxygen vacancies (A‐Vo‐SnO2) is fabricated to achieve visible‐light‐driven photocatalytic CO2 reduction. Specifically, amino groups modified onto the surface of the catalyst can provide more active sites to promote the adsorption of CO2. Meanwhile, the synchronously induced oxygen defect level reduces the band‐gap energy and expands the light‐absorption region from UV light to visible light. The oxygen vacancies can modulate the electronic structure and work as the separation centers of spatial charges, thus promoting the interfacial charge transfer efficiency and providing more catalytic sites, as evidenced by experimental observation and theoretical calculation. As expected, this A‐Vo‐SnO2 exhibits a CH4 evolution rate of 17.27 µmol g−1 h−1 without adding sacrificial agent and co‐catalyst, much higher than 5.98 µmol g−1 h−1 of pure SnO2. This work can provide significant inspiration for the design of defect engineering based on visible‐light‐driven photocatalysts towards photocatalytic CO2 conversion.

Ionic Liquid Bridge Assisting Bifacial Defect Passivation for Efficient All-Inorganic Perovskite Cells with High Open-Circuit Voltage.

Serious open-circuit voltage (Voc) loss originating from nonradiative recombination and mismatch energy level at TiO2/perovskite buried interface dramatically limits the photovoltaic performance of all-inorganic CsPbIxBr3-x (x = 1, 2) perovskite solar cells (PSCs) fabricated through low-temperature methods. Here, an ionic liquid (IL) bridge is constructed by introducing 1-butyl-3-methylimidazolium acetate (BMIMAc) IL to treat the TiO2/perovskite buried interface, bilaterally passivate defects and modulate energy alignment. Therefore, the Voc of all-inorganic CsPbIBr2 PSCs modified by BMIMAc (Target-1) significantly increases by 148 mV (from 1.213 to 1.361 V), resulting in the efficiency increasing to 10.30% from 7.87%. Unsealed Target-1 PSCs show outstanding long-term and thermal stability. During the accelerated degradation process (85 °C, RH: 50∼60%), the Target-1 PSCs achieve a champion PCE of 11.94% with a remarkable Voc of 1.403 V, while the control PSC yields a promising PCE of 10.18% with a Voc of 1.319 V. In particular, the Voc of 1.403 V is the highest Voc reported so far in carbon-electrode-based CsPbIBr2 PSCs. Moreover, this strategy enables the modified all-inorganic CsPbI2Br PSCs to achieve a Voc of 1.295 V and a champion efficiency of 15.20%, which is close to the reported highest PCE of 15.48% for all-inorganic CsPbI2Br PSCs prepared by a low-temperature process. This study provides a simple BMIMAc IL bridge to assist bifacial defect passivation and elevate the photovoltaic performance of all-inorganic CsPbIxBr3-x (x = 1, 2) PSCs.

How negative feedback and the ambient environment limit the influence of recombination in common envelope evolution

ABSTRACT We perform 3D hydrodynamical simulations to study recombination and ionization during the common envelope (CE) phase of binary evolution, and develop techniques to track the ionic transitions in time and space. We simulate the interaction of a $2\, \mathrm{M_\odot }$ red giant branch primary and a $1\, \mathrm{M_\odot }$ companion modelled as a particle. We compare a run employing a tabulated equation of state (EOS) that accounts for ionization and recombination, with a run employing an ideal gas EOS. During the first half of the simulations, ∼15 per cent more mass is unbound in the tabulated EOS run due to the release of recombination energy, but by simulation end the difference has become negligible. We explain this as being a consequence of (i) the tabulated EOS run experiences a shallower inspiral and hence smaller orbital energy release at late times because recombination energy release expands the envelope and reduces drag, and (ii) collision and mixing between expanding envelope gas, ejecta and circumstellar ambient gas assists in unbinding the envelope, but does so less efficiently in the tabulated EOS run where some of the energy transferred to bound envelope gas is used for ionization. The rate of mass unbinding is approximately constant in the last half of the simulations and the orbital separation steadily decreases at late times. A simple linear extrapolation predicts a CE phase duration of ${\sim}2\, {\rm yr}$, after which the envelope would be unbound.