Time-resolved Decay Research Articles

Facile fabrication of BUC-21/Bi24O31Br10 composites for enhanced photocatalytic Cr(VI) reduction under white light

In this study, the Bi24O31Br10 nanosheets were successfully synthesized using hydrothermal method. Subsequently, series binary BUC-21/Bi24O31Br10 composites were fabricated by facile ball-milling method. The results suggested that the introduction of a specific quality of Bi24O31Br10 on the surface of BUC-21 could enhance the utilization efficiency of white light and suppress the photo-induced carriers recombination to promote the photocatalytic efficiency. The BB-100 (the mass ratio of BUC-21/Bi24O31Br10 being 1) exhibited the best performance, in which 99.9% Cr(VI) ions were photoreduced into Cr(III) upon the white light irradiation within 120 min. As well, the influences of small organic acids, initial pH, light intensities along with the co-existing matters on the Cr(VI) removal were investigated. Furthermore, the Box-Behnken experimental design methodology proved that the photoreduction process was significantly influenced by the co-existing inorganic anions and negatively charged dissolved organic matters (DOM). After 4-run recycling for the adsorption-photoreduction of Cr(VI) experiments, the BB-100 still exhibited satisfied reduction activity with good stability and reusability. A possible reaction mechanism was proposed and clarified through the electrochemical determination, time-resolved photoluminescence decay spectra, active species trapping experiments, electron spin resonance analyses (ESR) and density functional theory (DFT) calculation.

Excellent visible light photocatalytic efficiency of Na and S co-doped g-C3N4 nanotubes for H2 production and organic pollutant degradation

Na and S co-doped g-C3N4 nanotubes (NaxSCNNTs) were synthesized via thermal polymerization using NaHCO3 and thiourea as Na and S source, respectively. The co-doping of Na and S in g-C3N4 nanotubes was verified by FTIR, SEM elemental mapping and XPS measurements. After loading Pt, the optimal Na0.1SCNNT produced H2 at a rate of 173.7 μmol h−1, which is 1.76 times and 14 times of that of Na0SCNNT and bulk g-C3N4, respectively. Moreover, the performance of Na0.1SCNNT was increased by 50% after replacing Pt with PtCo. The apparent quantum efficiency of Na0.1SCNNT/Pt and Na0.1SCNNT/PtCo were 6.7% and 10.2% at λ = 420 nm, respectively. Na0.1SCNNT also displayed the best photocatalytic activity for both p-chlorophenol and rhodamine B degradation, which are 3.1 and 3.4 times of that of bulk g-C3N4, respectively. Cyclic photocatalytic experiments demonstrated the high stability of Na0.1SCNNT. The enhanced photocatalytic activity of Na0.1SCNNT is resulted from the large specific surface area, narrowed bandgap, enhanced visible light absorption, and down-shifted valance band, which are supported by steady-state PL spectra and time-resolved transient PL decay, as well as photoelectrochemical analysis. Finally, the possible photocatalytic mechanisms for H2 production, and degradation of rhodamine B and p-chlorophenol are proposed.

Highly efficient visible-light photoactivity of Z-scheme MoS2/Ag2CO3 photocatalysts for organic pollutants degradation and bacterial inactivation

Here, a novel Z-scheme MoS2/Ag2CO3 heterojunction photocatalyst was assembled from two-dimensional MoS2 nanosheets and Ag2CO3 nanoparticles through facile hydrothermal and in-situ precipitation method. The MoS2/Ag2CO3 heterojunction exhibited much enhanced visible-light photocatalytic performance in probe experiment for organic pollutants degradation and Escherichia coli (E. coli) inactivation compared to pristine Ag2CO3 and MoS2. The degradation rates of Lanasol Red 5B, rhodamine B, ciprofloxacin, and metronidazole reached 95%, 90%, 80%, and 72%, respectively. On the other hand, E. coli was completely inactivated in 80 min in the presence of 5%-MoS2/Ag2CO3. The improved photocatalytic performance was ascribed to the enhanced photogenerated charge separation efficiency and increased lifetime of the charge carriers, proved by photoluminescence spectra, time-resolved fluorescence emission decay spectra, and electrochemical measures. In addition, the active species trapping and ESR experiments all indicated that holes (h+) exhibited a significant contribution and superoxide radicals (O2−) acted as assistants. Based on experiment results, the photocatalytic enhancement mechanism for organic pollutants degradation and E. coli inactivation was discussed. The effect of representative environmental factors on the degradation of Lanasol Red 5B was investigated. The experiment results indicated that the degradation efficiency was partially influenced in the presence of inorganic salt. Furthermore, the appearance of a small amount of Ag nanoparticles not only enhanced the charge transfer, but also improved the stability of photocatalyst. Overall, MoS2/Ag2CO3 heterojunction has a great application potential for future water purification.

Novel BiSbO4/BiOBr nanoarchitecture with enhanced visible-light driven photocatalytic performance: Oxygen-induced pathway of activation and mechanism unveiling

Hetero-structured photocatalysts are known to accelerate the separation and migration of photo-induced carriers. In this study, we propose a novel BiSbO4/BiOBr hetero-structured nanocomposite with enhanced molecular oxygen activation property. The formation of heterojunctions in the synthesized catalyst is confirmed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analyses. Based on photoluminescence spectra (PL), time-resolved transient decay photoluminescence spectra, and photoelectrochemical tests, it was shown that photo-induced electron transfer in BiSbO4/BiOBr nanocomposites is faster than in pure BiSbO4 or BiOBr. The accelerated migration of electrons promotes the activation of molecular oxygen and ultimately, enhances the degradation of Rhodamine B (RhB). Density function theory (DFT) calculations and electron spin resonance (ESR) tests indicate that the photo-induced electrons flow from BiOBr to BiSbO4, leading to faster separation of photo-generated electron-hole pairs and further production of superoxide radicals. Liquid chromatography mass spectrometry (LC-MS) analyses were also conducted in order to identify the intermediates of RhB degradation. Knowing that the photocatalytic reaction is activated by an oxygen-induced pathway, it is possible to propose a mechanism for the degradation of RhB based on the identified intermediates.

Interaction of a sphingolipid with human serum albumin in the native, thermally denatured and chemically denatured states: Emission wavelength-dependent photophysical revelation

The present study exhibits a spectroscopic deciphering of the effect of a phosphosphingolipid, sphingomyelin (SM), on native as well as thermally disrupted (at ~65 °C), and urea-induced partially (in the presence of ~4.5 M urea) and completely (in the presence of ~8 M urea) chemically denatured human serum albumin (HSA). The steady-state absorption studies reveal ground-state complex formation between SM and the serum albumin. The modulations in the steady-state emission spectral profile of the Trp residue in HSA along with the time-resolved fluorescence measurements depict SM-induced modification of the micro-environment around the sole Trp residue of HSA in all the studied cases, with no significant structural modification of the protein. However, monitoring the emission wavelength-sensitive time-resolved decay behaviour of Trp, keeping the excitation wavelength constant, in the absence and presence of SM in all the cases provides an interesting result depicting a progressive increase of average fluorescence lifetime of Trp upon shifting the monitoring emission wavelength gradually to the red end of the spectrum. A significantly greater extent of increase in the average lifetime of Trp with added SM compared to that in the absence of the lipid in case of completely chemically denatured HSA than those in the other studied cases provides a probable indication that SM modifies the solvation structure of the microenvironment around Trp in presence of 8 M urea most effectively and thus leading to a significant modulation of the solvation dynamics of the flourophore in its excited-state.

Studies of Ultrafast Transient Absorption Spectroscopy of Gold Nanorods in an Aqueous Solution.

Herein, ultrafast transient absorption spectroscopy is performed to probe the electron transfer studies between aqueous solution and gold nanorods (Au NRs). The seed-mediated growth method is used to synthesize crystalline cylindrical Au NRs having longitudinal plasmon resonance peak maximum at 825 nm. The as-synthesized Au NRs show average width and length of ∼10 ± 2 and ∼50 ± 2 nm, respectively, with an aspect ratio in the range of ∼5. The time-resolved decay profiles have been studied in a subpicosecond resolution range using pump wavelength at 410 nm excitation and probe wavelengths from visible to near-infrared region. The plasmon dynamics studies of Au NRs depend on the electron heating phenomena, coherent acoustic phonon vibration and electronic transient behavior, i.e., electron–phonon coupling, and homogenous dephasing processes. Thus, the obtained results highlighted that the ultrafast charge transfer dynamics studies in Au NRs could play an important role to elucidate their electronic, photothermal, and optical properties for molecular imaging, photothermal therapy, and optoelectronic and light-harvesting devices.

Phonon-Assisted Trapping and Re-excitation of Free Carriers and Excitons in Lead Halide Perovskites

Despite the advances in solar cells based on lead halide perovskites, the nature of photogenerated charges and trap states within these materials remains unclear. A model describing recombination in CH3NH3PbI3−xClx has been developed that accounts for phonon-assisted free-exciton and free-carrier trapping. We utilize optical spectroscopies and observe significant co-existence of the tetragonal and orthorhombic structural phases at low temperatures. From these measurements, we evaluate the longitudinal−optical phonon energy, exciton binding energy, and temperature-dependent electronic bandgap. We use these parameters to model the temperature- and fluence-dependent time-resolved photoluminescence decays, enabling us to demonstrate how shallow traps from which carriers can be re-excited can account for the delayed recombination in lead halide perovskites. The trap-state density reaches a maximum at the tetragonal to orthorhombic phase transition at ∼140 K, suggesting the formation of disorder-induced trap states, which are shown to dominate the recombination dynamics in CH3NH3PbI3−xClx.

The crystal structure and slow time-resolved oxidative decay of an E. coli DHFR complex with tetrahydrofolate with implications to drug design

The crystal structure and slow time-resolved oxidative decay of an <i>E. coli</i> DHFR complex with tetrahydrofolate with implications to drug design

Site-Selective Interaction of Human Serum Albumin with 4-Chloro-7-nitro-1,2,3-benzoxadiazole Modified Olanzapine Derivative and Effect of β-Cyclodextrin on Binding: In the Light of Spectroscopy and Molecular Docking.

Here, we present a detailed investigation on the interaction of 4-chloro-7-nitro-1,2,3-benzoxadiazole (NBD) embedded olanzapine derivative (OLA-NBD) with a model transport protein, human serum albumin (HSA). The thermodynamic parameters, ΔHo, ΔSo, and ΔGo, as evaluated by considering the van't Hoff relationship imply the major contribution of electrostatic/ionic interactions for the HSA-OLA-NBD association. The OLA-NBD induced quenching of HSA emission occurs through static quenching mechanism, indicating a 1:1 association, as portrayed from Benesi-Hildebrand plot, with ∼104 M-1 association constant value, and it is in good harmony with the value estimated from anisotropy experiment. The invariance of the time-resolved decay behavior of HSA with added OLA-NBD concentration, along with matching dependency of the binding constant (Kb) value on temperature, also supports the occurrence of static quenching. The effect of β-cyclodextrin on HSA-OLA-NBD binding is characterized by a smaller Kb value revealing that the OLA-NBD molecules are gradually removed from β-CD by HSA to achieve its medicinal outcome of drug delivery. The outcome from circular dichroism (CD) illustrates the variation of HSA secondary structure upon interaction with OLA-NBD. Concurrently, HSA-OLA-NBD association kinetics is also explored by applying the fluorescence technique. The possible interaction zone of OLA-NBD in HSA is investigated from AutoDock-based docking simulation study.

Copper(I)-Based Highly Emissive All-Inorganic Rare-Earth Halide Clusters

Summary The development of new environmentally friendly luminescent materials is crucial for future solid-state lighting, sensor, and display applications. Here, a Cu(I)-based all-inorganic rare-earth halide material, Rb 8 CuSc 3 Cl 18 , has been synthesized by a solid-state reaction method. In this compound, two Cu(I) ions are connected to three rare-earth halide octahedra to form a paddle-wheel-like cluster. The Cu(I) coordinated rare-earth halide clusters contribute to a strong blue photoluminescence emission. This Cu(I)-regulated emission can be extended to other isostructural compounds, such as Rb 8 CuY 3 Cl 18 . Moreover, the crucial role of Cu(I) has been illustrated by the isostructural non-emissive Rb 8 AgSc 3 Cl 18 . On the basis of comprehensive spectroscopy studies and density functional theory calculations, we found that Cu(I) photo-oxidation and correct orbital-energy-level alignment are crucial for the observed bright-blue emission through a proposed metal (Cu)-to-octahedra ([ScCl 6 ] 3− ) charge-transfer mechanism. The discovery of Cu(I)-based all-inorganic rare-earth halide clusters establishes a new strategy for constructing promising emissive halide materials.

Silicon nitride nanobeam enhanced emission from all-inorganic perovskite nanocrystals.

Optically active perovskite nanocrystals have shown considerable promise for a myriad of applications, such as single photon source, light-emitting diodes and nanophotonics. Coupling those nanocrystals to photonic micro- and nanostructures will offer additional degrees of freedom to manipulate their optical properties. Herein, we demonstrate the coupling of perovskite nanocrystals to a mechanically robust, poly(methyl-methacrylate) (PMMA)-encapsulated silicon nitride nanobeam photonic crystal cavity at room temperature. As determined from the time-resolved photoluminescence decay measurements, we observed enhanced spontaneous emission from the perovskite nanocrystals by a factor of 1.4, consistent with finite difference time domain simulation. In addition, by varying the concentration of the perovskite nanocrystal in the PMMA layer, the effective index of the layer can be modified, allowing us to tune the cavity mode resonance. Our results show that solution-processable perovskite nanocrystals hold a promising prospect for applications such as on-chip light sources, optoelectronic devices and photonic integrated circuits.

Solid-State Fluorescent Carbon Dots with Aggregation-Induced Yellow Emission for White Light-Emitting Diodes with High Luminous Efficiencies.

For practical applications of carbon dots (CDs), a major challenge is to prevent the notorious aggregation-caused quenching (ACQ) effect. Herein, a new type of CDs (CD1) has been developed that can transform from ACQ to an enhancement of fluorescence by aggregation-induced emission (AIE). The blue fluorescence of the CDs is suppressed by ACQ. However, this is accompanied by the phenomenon of AIE at a longer wavelength, resulting in the emergence and gradual enhancement of yellow fluorescence. The obtained CD1 solid powder shows a bright yellow emission with a photoluminescence quantum yield (PLQY) of 65%. The photoluminescence (PL) spectra, absorption spectra, and time-resolved PL decay curves indicate that Förster resonant energy transfer from dispersed CD1 particles to large CD1 agglomerations leads to the enhancement of yellow fluorescence. To exploit its high PLQY and strong AIE, CD1 is applied as a color-converting layer on blue light-emitting diode (LED) chips to fabricate white LEDs (WLEDs). The obtained devices show white light coordinates of (0.29, 0.38) and (0.32, 0.42), which are close to pure white light (0.33, 0.33), and luminous efficiencies of 97.8 and 93.9 lm·W-1 and show good stability. The low cost, easy fabrication, controllability, and favorable fluorescence properties signify that CD1 of AIE will have superior performance in a variety of applications.

Aqueously synthesized color-tunable quaternary Cu-In-Zn-S quantum dots for Cu(II) detection via mild and rapid cation exchange

Non-cadimum photoluminescent I−III−VI semiconductor nanocrystals have attracted increasing attention due to their low toxicity, extraordinary optical and electronic properties. Herein, water-soluble quaternary Cu-In-Zn-S quantum dots (CIZS QDs) with tunable emission from 535 nm to 645 nm were successfully synthesized via ecofriendly one-pot aqueous method. The full width at half-maximum (FWHM) of the emissions are about 68 nm–88 nm, which are rather narrow among Cu-based semiconductors and preferred to facilitate improving color purity. The photoluminescence of water-soluble QDs was enhanced by ZnS coating with the absolute quantum yield (QY) up to 30.8%. Further, a novel fluorescent sensor for Cu2+ detection was developed based on the alteration of intrinsic optical properties of the CIZS/ZnS QDs after cation exchange at room temperature within 10 min, presenting a linear range of 0.020–20 μM and a detection limit down to 6.7 nM. Mechanism studies revealed that the QDs served as the template for cation exchange, through UV–vis absorption and fluorescence spectra in combination with the chemical composition and time-resolved photoluminescence decay analysis. Ions interference experiments demonstrated the good selectivity of the QDs towards Cu2+ and the sensor showed comparable accuracy to ICP-AES method as well as good performance in real sample detection, manifesting the reliability of the current strategy for sensing Cu2+ mildly and rapidly.

Simultaneous removal of tetracycline and Cr(VI) by a novel three-dimensional AgI/BiVO4 p-n junction photocatalyst and insight into the photocatalytic mechanism

Simultaneous combination of photocatalytic oxidation of tetracycline (TC) and reduction of Cr(VI) over the AgI/BiVO4 p-n junction photocatalysts were studied systematically. The result showed that the pollutant degradation efficiency of the photocatalyst was greatly enhanced when the system contained both TC and Cr(VI) compared to that containing Cr(VI) or TC alone. It is proposed that the co-existence of oxidizable and reducible species, such as TC and Cr(VI), ensured efficient use of the photoinduced electrons and holes, which leaded high efficiencies for both TC oxidation and Cr(VI) reduction. Among these photocatalysts, the 0.3-AgI/BiVO4 exhibits excellent photocatalytic activity, which is ascribed to the increased lifetime of the charge carriers confirmed by the result of time-resolved fluorescence emission decay spectra. In addition, seven degradation products of TC were found by GC–MS. Moreover, the band structure of the photocatalyst was obtained by the DFT calculation, VB-XPS spectra and the values of the Fermi level obtained by CASTEP. Finally, simultaneous photocatalytic oxidation and reduction enhancing mechanism over the AgI/BiVO4 photocatalyst was discussed in detail. The strategy of forming novel p-n junction photocatalyst for both the Cr(VI) reduction and TC oxidation will benefit the development of the other new photocatalysts for the purpose of controlling and improving the environment.

Core Structure Engineering in Hole-Transport Materials to Achieve Highly Efficient Perovskite Solar Cells.

In this work, the thiadiazolopyridine (PT) unit was introduced as the core structure, with N3 ,N3 ,N6 ,N6 -tetrakis(4-methoxyphenyl)-9-phenyl-9 H-carbazole-3,6-diamine as the peripheral group, to obtain a new compound, JY8, for use as a hole-transport material (HTM) in planar perovskite solar cells (PSCs). Compared with the previously reported JY5 with benzothiadiazole as the core structure, the PT unit with stronger electron-withdrawing ability enhanced the intermolecular dipole-dipole interaction. Moreover, the introduction of the PT unit made the central part in JY8 more planar than its analogue JY5, which is conducive to charge transport. Field-emission (FE)-SEM images suggested a smooth and condense morphology of the JY8 film, which could improve the contact between the perovskite layer and the metal electrode. Space-charge limitation of current results, steady-state, and time-resolved photoluminescence decay curves indicated that JY8 as HTM facilitated hole extraction and hole transport. Consequently, planar PSCs fabricated with JY8 as the HTM exhibited a decent efficiency of 19.14 % with a high fill factor of 81 %.

Fluorescence lifetime imaging with a single-photon SPAD array using long overlapping gates: an experimental and theoretical study.

Developing large arrays of single-photon avalanche diodes (SPADs) with on-chip time-correlated single-photon counting (TCSPC) capabilities continues to be a difficult task due to stringent silicon real estate constraints, high data rates and system complexity. As an alternative to TCSPC, time-gated architectures have been proposed, where the numbers of photons detected within different time gates are used as a replacement to the usual time-resolved luminescence decay. However, because of technological limitations, the minimum gate length implement is on the order of nanoseconds, longer than most fluorophore lifetimes of interest. However, recent FLIM measurements have shown that it is mainly the gate step and rise/fall time, rather than its length, which determine lifetime resolution. In addition, the large number of photons captured by longer gates results in higher SNR. In this paper, we study the effects of using long, overlapping gates on lifetime extraction by phasor analysis, using a recently developed 512×512 time-gated SPAD array. The experiments used Cy3B, Rhodamine 6G and Atto550 dyes as test samples. The gate window length was varied between 11.3 ns and 23 ns while the gate step was varied between 17.86 ps and 3 ns. We validated the results with a standard TCSPC setup and investigated the case of multi-exponential samples through simulations. Results indicate that lifetime extraction is not degraded by the use of longer gates, nor is the ability to resolve multi-exponential decays.

Study the photocatalytic mechanism of the novel Ag/p-Ag2O/n-BiVO4 plasmonic photocatalyst for the simultaneous removal of BPA and chromium(VI)

Herein, we demonstrate the successful construction of a novel flowerlike Ag/p-Ag2O/n-BiVO4 plasmonic photocatalyst for the photocatalytic oxidation of BPA and reduction of chromium(VI) simultaneously under visible light irradiation. Among these samples, 2mM-Ag/p-Ag2O/n-BiVO4 exhibits the highest photocatalytic performances. The photocatalytic reduction and oxidation efficiency can achieve 69.8 and 91.9%, respectively, after 100 min visible-light irradiation. The enhancement mechanism for the plasmonic photocatalyst is explored, which can be attributed to the enhanced absorbance in the visible light region, and the facilitated charge transfer and the suppressed recombination of electron-hole pairs in the Ag/p-Ag2O/n-BiVO4. The results of the electrochemical impedance spectroscopy, the fluorescence emission spectra and the time-resolved fluorescence emission decay spectra indicate the enhanced charge separation in the Ag/p-Ag2O/n-BiVO4 plasmonic photocatalyst. In addition, the free radical scavenging test shows that h+ and OH radicals play crucial roles in the photocatalytic oxidation reaction. The photogenerated electrons in the photocatalytic reduction process, are confirmed by the DMPO spin-trapping technology. Moreover, the band structures of various photocatalysts are revealed via the valence band XPS spectra and the Fermi level obtained by CASTEP code.

Methods toward simplification of time resolved fluorescence anisotropy in proteins labeled with NBD (4-chloro-7-nitrobenzofurazan) adducts

The analysis of time resolved fluorescence anisotropy for NBD tagged proteins is difficult when multiple exponential components arise from heterogeneous amino acid fluorescent adducts. Two approaches were taken toward simplification. First, N terminal selective labeling of tear lipocalin with NBD-Cl was attempted at pH 7.0. While lysines were predominantly labeled at pH 8.0, selective N terminal labeling was attained at neutral pH. Second, fluorescence anisotropic decay analysis was simplified to recover only the rotational correlation time of the protein not the side chain. The boundaries for analysis of anisotropic decays were limited to the longer lifetimes. A modified tail fit enabled fitting the anisotropic decay to a single exponential. The correlation time for tear lipocalin matched published values. Additionally, a method for normalization of acquisition times of vertically (VV) and horizontally (VH) polarized fluorescence emission decays is presented for time-resolved anisotropy. Here it is applied to Picoharp software (Picoquant, Berlin). Picoharp software is programmed with an automatic stop at unequal acquisition times if the fluorescent counts exceeds a default. The method adjusts the intensity decays to the same acquisition time and is applicable to all time-resolved anisotropic decay data collected with time-correlated photon counting.•NBD labeling at pH 7.0 was not selective for N terminus of LCN1.•Constraints for range simplifies fittings of anisotropic decays.•Different acquisition times for decays can be normalized to facilitate fitting in data obtained by Picoharp.

Novel π-extended porphyrin-based hole-transporting materials with triarylamine donor units for high performance perovskite solar cells

Efficient hole transporting materials (HTMs) for perovskite solar cells (PrSCs) is highly desired in emerging solar cell technologies. Three HTMs comprising a coplanar porphyrin core with different substituted electron donating triarylamine (TAA) groups (coded as SGT-061, SGT-062, and SGT-063) were successfully developed and used as HTMs for PrSCs. The porphyrin-based HTMs with more bulky donor groups (SGT-062 and SGT-063) possess the larger dihedral angle between alkoxy-substituted phenyl ring and the donor TAA core, leading to the greater interference for the dense molecular arrangement and reducing the π-π stacking of HTM molecules. But SGT-061 with a less bulky donor enables a tight molecular arrangement to increase the π-π stacking between molecules. This renders SGT-061 to have a higher hole mobility than that of SGT-062 and SGT-063 HTMs with bigger donor groups. Moreover, the dynamic charge transfer process of perovskite/various HTM films was studied by time-resolved photoluminescence decay. And SGT-061 exhibited more efficient hole extraction ability than that of SGT-062 and SGT-063. This could be ascribed to better hole mobility and better co-facial π-π stacking between molecules. These results indicate that a less bulky electron donor unit is a preferred peripheral group for developing porphyrin based HTMs for efficient perovskite solar cells.

SnO2-rGO nanocomposite as an efficient electron transport layer for stable perovskite solar cells on AZO substrate

Electron transport layer (ETL) plays an important role in realizing efficient and stable perovskite solar cells (PSCs). There are continuous efforts in developing new types of low cost ETLs with improved conductivity and compatibility with perovskite and the conducting electrode. Here, in order to obtain high efficient and stable PSCs on ZnO:Al (AZO) substrate, reduced graphene oxide (rGO) is incorporated into SnO2 nanoparticles to form composite ETL. For planar PSC on AZO substrates, SnO2-rGO with a low incorporation ratio of 3 wt% rGO significantly enhances the device short circuit current density (Jsc) and the fill factor when compared to the device with pristine SnO2 ETL, leading to an overall power conversion efficiency of 16.8% with negligible hysteresis. The effectiveness of the excited charge transfer process of SnO2-rGO ETL is revealed by time-resolved photoluminescence decay, and by electrochemical impedance spectrum measurements. Furthermore, the solar cell stability is also enhanced due to the incorporation of rGO in the ETL. This work provides a low cost and effective ETL modification strategy for achieving high performance planar PSCs.