Adsorption and diffusion of CO2 and CH4 in covalent organic frameworks: an MC/MD simulation study

Covalent organic frameworks (COFs) are a promising gas separation material which have been developed recently. In this work, we have used grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations to investigate the adsorption and diffusion properties of CO₂ and CH₄ in five recent synthesised COF materials. We have also considered the properties of amino-modified COFs by adding –NH₂ group to the five COFs. The adsorption isotherm, adsorption/diffusion selectivity, self/transport diffusion coefficients have been examined and discussed. All of the five COFs exhibit promising adsorption selectivity which is higher than common nanoporous materials. An S-shaped adsorption isotherm can be found for CO₂ instead of CH₄ adsorption. The introduction of –NH₂ group is effective at low pressure region (<200?kPa). The diffusion coefficients are similar for TS-COFs but increase with the pore size for PI-COFs, and the diffusion coefficients seem less dependent on the –NH₂ groups.     

Relating Recombination,Density of States,and Device Performance in an Efficient Polymer:Fullerene Organic Solar Cell Blend

We explore the interrelation between density of states, recombination kinetics, and device performance in efficient poly[4,8‐bis‐(2‐ethylhexyloxy)‐benzo[1,2‐b:4,5‐b']dithiophene‐2,6‐diyl‐alt‐4‐(2‐ethylhexyloxy‐1‐one)thieno[3,4‐b]thiophene‐2,6‐diyl]:[6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PBDTTT‐C:PC₇₁BM) bulk‐heterojunction organic solar cells. We modulate the active‐layer density of states by varying the polymer:fullerene composition over a small range around the ratio that leads to the maximum solar cell efficiency (50–67 wt% PC₇₁BM). Using transient and steady‐state techniques, we find that nongeminate recombination limits the device efficiency and, moreover, that increasing the PC₇₁BM content simultaneously increases the carrier lifetime and drift mobility in contrast to the behavior expected for Langevin recombination. Changes in electronic properties with fullerene content are accompanied by a significant change in the magnitude or energetic separation of the density of localized states. Our comprehensive approach to understanding device performance represents significant progress in understanding what limits these high‐efficiency polymer:fullerene systems.     

The Role of Exciton Ionization Processes in Bulk Heterojunction Organic Photovoltaic Cells

To realize efficient photoconversion in organic semiconductors, photogenerated excitons must be dissociated into their constituent electronic charges. In an organic photovoltaic (OPV) cell, this is most often accomplished using an electron donor–acceptor (D–A) interface. Interestingly, recent work on MoO_x/C₆₀ Schottky OPVs has demonstrated that excitons in C₆₀ may also undergo efficient bulk‐ionization and generate photocurrent as a result of the large built‐in field created by the MoO_x/C₆₀ interface. Here, it is demonstrated that bulk ionization processes also contribute to the short‐circuit current density (J_SC) and open‐circuit voltage (V_OC) in bulk heterojunction (BHJ) OPVs with fullerene‐rich compositions. Temperature‐dependent measurements of device performance are used to distinguish dissociation by bulk‐ionization from charge transfer at the D–A interface. In optimized fullerene‐rich BHJs based on the D–A pairing of boron subphthalocyanine chloride (SubPc)–C₆₀, bulk‐ionization is found to be responsible for ≈16% of the total photocurrent, and >30% of the photocurrent originating from C₆₀. The presence of bulk‐ionization in C₆₀ also impacts the temperature dependence of V_OC, with fullerene‐rich SubPc:C₆₀ BHJ OPVs showing a larger V_OC than evenly mixed BHJs. The prevalence of bulk‐ionization processes in efficient, fullerene‐rich BHJs underscores the need to include these effects when engineering device design and morphology in OPVs.     

Chemical Exfoliation as a Controlled Route to Enhance the Anodic Performance of COF in LIB

A covalent organic framework (COF), built from light atoms with a graphitic structure, could be an excellent anodic candidate for lightweight batteries, which can be of use in portable devices. But to replace the commercial graphite anode, they need more Li‐interactive sites/unit‐cell and all such sites should be made to participate. The compromise made in the volumetric density to gain the gravimetric advantage should be minimal. Exfoliation enhances surface/functional group accessibility yielding high capacity and rapid charge storage. A chemical strategy for simultaneous exfoliation and increase of Li‐loving active‐pockets can deliver a lightweight Li‐ion battery (LIB). Here, anthracene‐based COFs are chemically exfoliated into few‐layer‐thick nanosheets using maleic anhydride as a functionalizing exfoliation agent. It not only exfoliates but also introduces multiple Li‐interactive carbonyl groups, leading to a loading of 30 Li/unit‐cell (vs one Li per C₆). The exfoliation enhances the specific capacity by ≈4 times (200–790 mAh g^?1 @100 mA g^?1). A realistic full‐cell, made using the exfoliated COF against a LiCoO₂ cathode, delivers a specific capacity of 220 mAh g^?1 over 200 cycles. The observed capacity stands highest among all organic polymers. For the first report of a COF derived full‐cell LIB, this is a windfall.     

Differences in the adsorption and diffusion behaviour of water and non-polar gases in nanoporous carbon: role of cooperative effects of pore confinement and hydrogen bonding

We investigate the effect of pore confinement and molecular geometry on the adsorption and self-diffusion of H₂O, CO₂, Ar, CH₄, C₃H₆, SF₆ and C₅H₁₂, in a realistic model of nanoporous silicon carbide derived carbon (SiC-DC), constructed using hybrid reverse Monte Carlo simulation. Adsorption isotherms, adsorbate–adsorbate and adsorbate–adsorbent contributions to the isosteric heat of adsorption are determined to study the effect of pore confinement, microporosity and molecular geometry on adsorption of these gases. We describe the cooperative effect of pore confinement and hydrogen bonding on the formation of water clusters and anomalous adsorption behaviour of water compared with non-polar gases. We find that, in contrast to literature results based on the slit-pore model, pore-filling does not occur below the saturation pressure in hydrophobic amorphous carbon materials such as SiC-DC and activated carbon fibre. We also compare self-diffusivities and activation energy barriers of water and non-polar gases in the microporous structure of SiC-DC to identify underlying correlations with molecular properties. We demonstrate that the self-diffusivity of water deviates considerably from the correlation between diffusivity and molecular kinetic diameter observed for non-polar gases. This is attributed to the reduced diffusivity of water, and its relatively large energy barrier at high loadings despite its small kinetic diameter, which is due to the blocking effect of water clusters at pore entries.     

Using Ultralow Dosages of Electron Acceptor to Reveal the Early Stage Donor–Acceptor Electronic Interactions in Bulk Heterojunction Blends

Tuning the donor–acceptor (D–A) weight ratio is an essential step to optimize the performance of a bulk heterojunction (BHJ) solar cell. The unoptimized regime with a low acceptor concentration is generally unexplored despite it may reveal the early stage electronic D–A interactions. In this study, PTB7:PC₇₁BM is used to examine factors that limit the device performance in unoptimized regime. The key limiting factor is the creation of traps and localized states originated from fullerene molecules. Photothermal deflection spectroscopy is used to quantify the trap density. Starting with pristine PTB7, addition of small concentration of fullerene increases the electron trap density and lowers the electron mobility. When the D–A weight ratio reaches 1:0.1, fullerene percolation occurs. There is an abrupt drop in trap density and simultaneously a six orders of magnitude increase in the electron mobility. Furthermore, the fill factors of the corresponding photovoltaic devices are found to anticorrelate with the trap density. This study reveals that electron trapping is the key limiting factor for unoptimized BHJ solar cells in low fullerene regime.     

Photosensitized covalent organic framework as a light-induced oxidase mimic for colorimetric detection of uric acid

As large numbers of people are suffering from gout, an accurate, rapid, and sensitive method for the detection of gout biomarker, uric acid, is important for its effective control, diagnosis, and therapy. Although colorimetric detection methods based on uricase have been considered, they still have limitations as they produce toxic H₂O₂ and are expensive and not stable. Here, a novel uricase-free colorimetric method was developed for the sensitive and selective detection of uric acid based on the light-induced oxidase-mimicking activity of a new photosensitized covalent organic framework (COF) (2,4,6-trimethylpyridine-3,5-dicarbonitrile–4-[2-(4-formylphenyl)ethynyl]benzaldehyde COF [DCTP–EDA COF]). DCTP–EDA COF has a strong ability to harvest visible light, and it could catalyze the oxidation of 1,4-dioxane, 3,3′,5,5′-tetramethylbenzidine under visible light irradiation to produce obvious color changes. With the addition of uric acid, however, the significant inhibition of the oxidase-mimicking activity of DCTP–EDA COF remarkably faded the color, and thus uric acid could be colorimetrically detected in the range of 2.0–150 μM with a limit of detection of 0.62 μM (3σ/K). Moreover, the present colorimetric method exhibited high selectivity; uric acid level in serum samples was successfully determined, and the recoveries ranged from 96.5% to 105.64%, suggesting the high accuracy of the present colorimetric method, which demonstrates great promise in clinical analysis.     

Quantitating intraparticle O2 gradients in solid supported enzyme immobilizates: Experimental determination of their role in limiting the catalytic effectiveness of immobilized glucose oxidase

Enzymatic O₂‐dependent oxidations are receiving increased attention for use in fine chemicals synthesis. Solid supported oxidation catalysts often show poor efficiency due to pronounced O₂ diffusion restriction. Internal O₂ supply therefore constitutes a key parameter for optimizing the enzyme immobilization. We herein describe an optical sensing method for quantitation of space‐averaged intraparticle O₂ concentrations in porous Sepabeads carriers. The method applies phosphorescence lifetime measurements on Sepabeads labeled with an O₂ sensitive indicator dye. Using glucose oxidase immobilized at different loadings (0.005–12 mg/g) on labeled Sepabeads, we analyzed in real time during the enzymatic reaction the formation of O₂ concentration differences between bulk liquid and the intraparticle environment. We show that the O₂ gradient at apparent steady state increased with increasing enzyme loading, so that O₂ eventually became totally depleted from inside the highly loaded carriers. We also show that the residual intraparticle O₂ concentration was correlated with the catalytic effectiveness factor (η) of the enzyme immobilizate used, thus providing a direct measure of the magnitude of O₂ diffusion limitation. Once corrected for diffusional effect, η was no longer dependent on enzyme loading and its constant value now described the intrinsic activity of immobilized glucose oxidase. Three common procedures of enzyme immobilization, involving adsorption, cross‐linking, and covalent attachment, are shown to differ widely concerning the obtained intrinsic activity. Therefore, intraparticle O₂ concentration data enable distinction between diffusional restriction and activity loss as the two principal factors limiting the effectiveness of immobilized O₂ dependent enzymes, and thus they inform rational design of an optimally active oxidation biocatalyst on solid support. Biotechnol. Bioeng. 2013; 110: 2086–2095. © 2013 Wiley Periodicals, Inc.     

Toxic effect of Aβ<Subscript>25–35</Subscript> and fullerene C<Subscript>60</Subscript> on erythrocytes

Using light microscopy and spectrophotometry, it has been shown that amyloid β-peptide Aβ_25–35 and water-soluble fullerene C₆₀ cause lysis of human and rat erythrocytes. Both fullerene C₆₀ and Aβ_25–35 partly inhibited the activities of membrane-associated phosphofructokinase and cytoplasmic lactate dehydrogenase in erythrocytes.     

Quantitative analysis of C60 fullerene in blood and tissues by high-performance liquid chromatography with photodiode-array and mass spectrometric detection

A high-performance liquid chromatographic (HPLC) assay method for C₆₀ fullerene, in blood, liver and spleen using photodiode-array detection or mass spectrometric detection (LC–MS) and C₇₀ fullerene, as the internal standard, is described. The recovery from mouse blood and tissues spiked with micronized C₆₀ exceeds 90%. The method is linear from 0.05 to 200 mg of C₆₀ per liter of blood and from 0.05 to 5.00% of C₆₀ per tissue weight. The limit of detection of the method is 0.1 ng of C₆₀ per injection. This method was applied to mouse blood and tissue samples after intraperitoneal administration of a micronized C₆₀ suspension.     

Molecular Understanding of the Open‐Circuit Voltage of Polymer:Fullerene Solar Cells

The origin of open‐circuit voltage (V_OC) was studied for polymer solar cells based on a blend of poly(3‐hexylthiophene) (P3HT) and seven fullerene derivatives with different LUMO energy levels and side chains. The temperature dependence of J–V characteristics was analyzed by an equivalent circuit model. As a result, V_OC increased with the decrease in the saturation current density J₀ of the device. Furthermore, J₀ was dependent on the activation energy E_A for J₀, which is related to the HOMO–LUMO energy gap between P3HT and fullerene. Interestingly, the pre‐exponential term J₀₀ for J₀ was larger for pristine fullerenes than for substituted fullerene derivatives, suggesting that the electronic coupling between molecules also has substantial impact on V_OC. This is probably because the recombination is non‐diffusion‐lmilited reaction depending on electron transfer at the P3HT/fullerene interface. In summary, the origin of V_OC is ascribed not only to the relative HOMO–LUMO energy gap but also to the electronic couplings between fullerene/fullerene and polymer/fullerene.     

Low‐Overpotential Electrocatalytic Water Splitting with Noble‐Metal‐Free Nanoparticles Supported in a sp3 N‐Rich Flexible COF

Covalent organic frameworks (COFs) are crystalline organic polymers with tunable structures. Here, a COF is prepared using building units with highly flexible tetrahedral sp³ nitrogens. This flexibility gives rise to structural changes which generate mesopores capable of confining very small (<2 nm sized) non‐noble‐metal‐based nanoparticles (NPs). This nanocomposite shows exceptional activity toward the oxygen‐evolution reaction from alkaline water with an overpotential of 258 mV at a current density of 10 mA cm^?2. The overpotential observed in the COF‐nanoparticle system is the best in class, and is close to the current record of ≈200 mV for any noble‐metal‐free electrocatalytic water splitting system—the Fe–Co–Ni metal‐oxide‐film system. Also, it possesses outstanding kinetics (Tafel slope of 38.9 mV dec^?1) for the reaction. The COF is able to stabilize such small‐sized NP in the absence of any capping agent because of the COF–Ni(OH)₂ interactions arising from the N‐rich backbone of the COF. Density‐functional‐theory modeling of the interaction between the hexagonal Ni(OH)₂ nanosheets and the COF shows that in the most favorable configuration the Ni(OH)₂ nanosheets are sandwiched between the sp³ nitrogens of the adjacent COF layers and this can be crucial to maximizing their synergistic interactions.     

Underlying mechanisms of symmetric calcium wave propagation in rat ventricular myocytes

Calcium waves in heart cells are mediated by diffusion-coupled calcium-induced calcium release. The waves propagate in circular fashion. This is counterintuitive in view of the accepted ultrastructure of the cardiac myocyte. The density of calcium release sites in the transverse direction is four times higher than in the longitudinal direction. Simulations with release sites localized along Z-lines and isotropic diffusion yielded highly elliptical, nonphysiological waves. We hypothesized that subcellular organelles counteracted the higher release site density along the Z-lines by acting as transverse diffusion barriers and sites of active calcium uptake. We quantified the reduction of transverse diffusion by microinjecting cells with the nonreactive dye fluorescein. The ratio of the radial diffusion coefficient to the longitudinal coefficient was 0.39. Inhibition of mitochondrial uptake by rotenone accelerated the wave in the transverse direction. Simulations with release sites clustered at the Z-lines and a transverse diffusion coefficient 50% of the longitudinal coefficient generated waves of ellipticity 2/1 (major axis along the Z-line). Introducing additional release sites between the Z-lines at a density 20% of that on the Z-lines produced circular waves. The experiments and simulations support the presence of transverse diffusion barriers, additional uptake sites, and possibly intermediate release sites as well.     

The Imine‐Based COF TpPa‐1 as an Efficient Cooling Adsorbent That Can Be Regenerated by Heat or Light

Adsorption‐based cooling systems, which can be driven by waste heat and solar energy, are promising alternatives to conventional, compression‐based cooling systems, as they demand less energy and emit less CO₂. The performance of adsorption‐based cooling systems relates directly to the performance of the working pairs (sorbent–water). Accordingly, improvement of these systems relies on the continual discovery of new sorbents that enable greater mass exchange while requiring less energy for regeneration. Here, it is proposed that covalent‐organic frameworks (COFs) can replace traditional sorbents for adsorption‐based cooling. In tests mimicking standard operating conditions for industry, the imine‐based COF TpPa‐1 exhibits a regeneration temperature below 65 °C and a cooling coefficient of performance of 0.77 – values which are comparable to those reported for the best metal–organic framework sorbents described to date. Moreover, TpPa‐1 exhibits a photothermal effect and can be regenerated by visible light, thereby opening the possibility for its use in solar‐driven cooling.     

Antiamyloid properties of fullerene C<Subscript>60</Subscript> derivatives

A comparative estimation of the ability of complexes of fullerene C₆₀ with polyvinylpyrrolidone and fullerene C₆₀ derivatives (the sodium salt of the polycarboxylic derivative of fullerene C₆₀, sodium fullerenolate), has been carried out. The fullerenes destroyed amyloid fibrils of the Aβ(1–42) peptide of the brain and the muscle X-protein. A study of the effect of fullerenes on muscle actin showed that complexes of fullerene C₆₀ with polyvinylpyrrolidone and sodium fullerenolate did not prevent the filament formation of actin, nor did they destroy its filaments in vitro. Conversely, sodium salt of the polycarboxylic derivative of fullerene C₆₀ destroyed actin filaments and prevented their formation. It was concluded that sodium fullerenolate and complexes of fullerene C₆₀ with polyvinylpyrrolidone are the most effective antiamyloid compounds among the fullerenes examined.     

Generalized Mechanochemical Synthesis of Biomass‐Derived Sustainable Carbons for High Performance CO2 Storage

Novel mechanochemical activation generates biomass‐derived carbons with unprecedented CO₂ storage capacity due to higher porosity than analogous conventionally activated carbons but similar pore size. The mechanochemical activation, or so‐called compactivation, process involves compression, at 740 MPa, of mixtures of activating agent (KOH) and biomass hydrochar into pellets/disks prior to thermal activation. Despite the increase in surface area and pore volume of between 25% and 75% compared to conventionally activated carbons, virtually all of the porosity of the biomass (sawdust and lignin) derived mechanochemically activated carbons is from small micropores (5.8–6.5 Å), which results in a dramatic increase in CO₂ storage capacity at 25 °C and low pressure (≤1 bar). The ambient temperature CO₂ uptake for a carbon derived from sawdust at 600 °C and a KOH/carbon ratio of 2, rises from 1.3 to 2.0 mmol g^?1 at 0.15 bar, and from 4.3 to 5.8 mmol g^?1 at 1 bar, which is the highest ever reported for carbonaceous materials. The mechanochemically activated carbons have a superior CO₂ working capacity for pressure swing adsorption and vacuum swing adsorption processes and, due to a high packing density, they exhibit excellent volumetric CO₂ uptake that is higher than for any material reported to date.     

Simulation of separation of C2H6 from CH4 using zeolitic imidazolate frameworks

Separation of important chemical feedstocks, such as C₂H₆ from natural gas, can greatly benefit the petrochemical industry. In this paper, the grand canonical Monte Carlo method has been used to study the adsorption and separation of CH₄ and C₂H₆ in zeolites, isoreticular metal-organic framework-1 (IRMOF-1) and zeolitic imidazolate frameworks (ZIFs) with different topology, including soadlite, gmelinite and RHO topologies. Compared with mordenite zeolite and IRMOF-1, ZIFs and mordenite framework inverted (MFI) zeolite have better separation performance for C₂H₆/CH₄ mixtures at different mole fractions of C₂H₆. From the study of equilibrium snapshots and density distribution profiles, adsorption sites could be grouped as (1) sites with strong interactions with adsorbent and (2) sites with strong interactions with surrounding adsorbates. The gas molecules occupied the first site and then went on to occupy the second site. In CH₄/C₂H₆ mixture adsorption/separation, the adsorption of CH₄ was confined by the existence of C₂H₆. Due to energetic effect, C₂H₆ selectivity was affected by temperature at a low-pressure range, but did not change as much in a high-pressure range because of packing effect in micropore. In binary adsorption, large C₂H₆ molecules favour sites with strong adsorbent interactions. At high pressures, packing effects played an important role and it became easy for small CH₄ molecules to access the sites with strong adsorbate interactions.     

Anisotropic rotational motions of poly(L-glutamic acid) in the alpha-helix conformation

The anisotropic rotational motion of the backbone and the side chains of poly(L -glutamic acid) in the α-helical structure was investigated using the ¹³C-T₁ and T₂ relaxation times of all carbon atoms with directly attached protons, obtained at a ¹³C-Larmor frequency of 67.89 MHz. The evaluation of the nmr data was carried out according to the previously derived anisotropic diffusion model, in which the macromolecule is considered a rigid rod. The rotation of the backbone is characterized by two diffusion constants, D₁ and D₃, describing the rotation perpendicular to and around the symmetry axis. The additional internal motion of the C^β-methylene group is described as a jump process with a jump rate, k₁, between two allowed rotametric states. Steric considerations indicate that the occupation of the third rotameric position is forbidden. The rotation of the C^γ-methylene group is decribed as a one-dimensional diffusion process around the C^β–C^γ bond. Investigation of the temperature dependence of the relaxation parameters led to the temperature dependence of the dynamic parameters. Activation energies were determined from these data. The dynamic parameters obtained for poly(L -glutamic acid) at 291 K are compared with the corresponding results of a previous study of poly(L -lysine). The development of an anisotropic diffusion model for the motions of the rod-shaped poly(L -lysine) α-helix and its application to the interpretation of the ¹³C-relaxation data of this molecule have already been published previously. In this model, both the overall molecular tumbling and the various internal motions have been characterized by diffusion constants or jump rates typical for each process. These dynamic parameters can be calculated from the spin–lattice relaxation times, the spin–spin relaxation times and the NOE factors of the C^α, C^β, and C^γ nuclei of the polypetide. In the present paper, we describe the application of the above-mentioned dynamic model to the interpretation of ¹³C-relaxation studies of a further homopolypeptide, poly(L -glutamic acid), in the α-helical structure. Furthermore, we studied the temperature dependence of the relaxation times of this polymer and determined the anisotropic diffusion parameters at each temperature. From their temperature dependence and from comparison of our present results with the data of our previous study of poly(L -lysine), we were able to derive new insights into the intramolecular diffusion processes and the excitation of various motions.     

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

The use of fullerene as acceptor limits the thermal stability of organic solar cells at high temperatures as their diffusion inside the donor leads to phase separation via Ostwald ripening. Here it is reported that fullerene diffusion is fully suppressed at temperatures up to 140 °C in bulk heterojunctions based on the benzodithiophene‐based polymer (the poly[[4,8‐bis[(2‐ethylhexyl)oxy]‐benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]‐thieno[3,4‐b]thiophenediyl]], (PTB7) in combination with the fullerene derivative [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₀BM). The blend stability is found independently of the presence of diiodooctane (DIO) used to optimize nanostructuration and in contrast to PTB7 blends using the smaller fullerene derivative PC₇₀BM. The unprecedented thermal stability of PTB7:PC₇₀BM layers is addressed to local minima in the mixing enthalpy of the blend forming stable phases that inhibit fullerene diffusion. Importantly, although the nanoscale morphology of DIO processed blends is thermally stable, corresponding devices show strong performance losses under thermal stress. Only by the use of a high temperature annealing step removing residual DIO from the device, remarkably stable high efficiency solar cells with performance losses less than 10% after a continuous annealing at 140 °C over 3 days are obtained. These results pave the way toward high temperature stable polymer solar cells using fullerene acceptors.     

Discerning the Surface and Bulk Recombination Kinetics of Organic–Inorganic Halide Perovskite Single Crystals

Organic–inorganic halide perovskite single crystals possess many outstanding properties conducive for photovoltaic and optoelectronic applications. However, a clear photophysics picture is still elusive, particularly, their surface and bulk photophysics are inexorably convoluted by the spectral absorbance, defects, coexisting photoexcited species, etc. In this work, an all‐optical study is presented that clearly distinguishes the surface kinetics from those of the bulk in the representative methylammonium‐lead bromide (MAPbBr₃) and ‐lead iodide (MAPbI₃) single crystals. It is found that the bulk recombination lifetime of the MAPbBr₃ single crystal is shortened significantly by approximately one to two orders (i.e., from ≈34 to ≈1 ns) at the surface with a surface recombination velocity of around 6.7 × 10³ cm s^?1. The surface trap density is estimated to be around 6.0 × 10¹⁷ cm^?3, which is two orders larger than that of the bulk (5.8 × 10¹⁵ cm^?3). Correspondingly, the diffusion length of the surface excited species is ≈130–160 nm, which is considerably reduced compared to the bulk value of ≈2.6–4.3 μm. Furthermore, the surface region has a wider bandgap that possibly arises from the strong lattice deformation. The findings provide new insights into the intrinsic photophysics essential for single crystal perovskite photovoltaics and optoelectronic devices.