Changes In Surface Potential Research Articles

Microscopic investigations on the surface-state dependent moisture stability of a hybrid perovskite.

Hybrid organic-inorganic perovskite (HOIP) materials have caught significant attention in photovoltaics and photoelectronics for their outstanding photovoltaic properties. However, their instability to various environment, such as illumination, temperature, moisture and oxygen, hinders their way to commercialization. To figure out the interaction mechanism between H2O and CH3NH3PbI3 (MAPbI3), extensive theoretical studies have been carried out; however, the experimental results are insufficient and inconsistent. Here, we systematically investigate and compare the influence of H2O on MAPbI3 perovskite films with or without DMF) post-annealing in dark or light condition. The interaction between H2O and the surface of pristine MAPbI3 leads to the fusion of grain boundaries thus grain growth into micron level in short-time moisture exposure. While the penetration of H2O into MAPbI3 results in swelled crystalline whisker, cracking into smaller grains in long-time exposure upon the release of H2O. However, no degradation occurs in dark condition. As the DMF post-annealing treatment changes the surface states of MAPbI3, the interactions between the external H2O and internal MAPbI3 significantly varies from the pristine MAPbI3. Three different surface states with different topographies have influence on the interaction process and mechanism with H2O, leading to different decomposition rates, the striped surface that is the most rough among the three and experiencing the minimum change in surface potential with exposure to 80% humidity decomposes into PbI2 fastest. However, the addition of light will once again affect the aforementioned process. It is found that even ambient light could severely speed up the moisture-induced decomposition of MAPbI3, while the N,N-dimethylformamide (DMF) post-annealing treatment significantly improves the stability of MAPbI3 films upon exposure to humidity and illumination, benefiting from the MAI-deficient thus H2O resistant surface.

The Equivalent Media Generated by Bubbles of High Contrasts: Volumetric Metamaterials and Metasurfaces

We deal with the point-interaction approximations for the acoustic wave fields generated by a cluster of highly contrasted bubbles for a wide range of densities and bulk moduli contrasts. We derive the equivalent fields when the cluster of bubbles is appropriately distributed (but not necessarily periodically) in a bounded domain $\Omega$ of $\mathbb{R}^3$. We handle two situations. 1. In the first one, we distribute the bubbles to occupy a $3$ dimensional domain. For this case, we show that the equivalent speed of propagation changes sign when the medium is excited with frequencies smaller or larger than (but not necessarily close to) the Minnaert resonance. As a consequence, this medium behaves as a reflective or absorbing depending on whether the used frequency is smaller or larger than this resonance. In addition, if the used frequency is extremely close to this resonance, for a cluster of bubbles with density above a certain threshold, then the medium behaves as a 'wall', i.e. allowing no incident sound to penetrate. 2. In the second one, we distribute the bubbles to occupy a $2$ dimensional (open or closed) surface, not necessarily flat. For this case, we show that the equivalent medium is modeled by a Dirac potential supported on that surface. The sign of the surface potential changes for frequencies smaller or larger than the Minnaert resonance, i.e. it behaves as a smart metasurface reducing or amplifying the transmitted sound across it. As in the $3$D case, if the used frequency is extremely close to this resonance, for a cluster of bubbles with density above an appropriate threshold, then the surface allows no incident sound to be transmitted across the surface, i.e. it behaves as a white screen.

AlGaN/GaN HEMT based sensor and system for polar liquid detection

In this paper, a GaN-high electron mobility transistor (HEMT) based sensor is designed, fabricated and characterized for polar liquid sensing. The fabricated HEMT sensor chip is packaged by using low temperature co-fired ceramic (LTCC) technique. The sensor shows a typical drain current of 21.2 mA at 3.3 V. The fabricated sensor shows a percentage change of 1.78%, 2.18% and 6.3% in drain current for mercury chloride, copper chloride and sodium chloride respectively with respect to the drain current of pure water. The readout circuit shows a change of 0.15, 0.20 and 0.34 mA in drain current for acetone, water and methanol respectively and ensures the detection of different polar liquids. Due to the novel inter-digital structure, the sensor shows a sensitivity of 5.98 mA/mm/Debye at a drain voltage of 3.3 V. Sensing mainly depends on the dipole moment because the change in the dipole moment of the liquid causes a change in surface potential at the gate sensing area. This paper gives a theoretical and practical perspective on polar liquid detection using both, the sensor and system.

Regulated surface potential impacts bioelectrogenic activity, interfacial electron transfer and microbial dynamics in microbial fuel cell

Influence of surface anode potential on the performance of microbial fuel cell (MFC) was evaluated by opting positive and negative poised anode potentials (+100/-100 mV) on two MFCs, and studied at two phases (during potential (DP) and post potential (PP)) along with a third MFC operated as control (no applied anode potential). Variation in physico-chemical factors as well as biocatalytic metabolic behavior was analyzed in terms of electron transfer, power density, electro-kinetics and microbial community. Post potential operation at −100 mV depicted rapid electron transfer, higher redox catalytic currents (−0.44/0.42 mA) and voltage (653 ± 28 mV) in comparison to other experimental conditions. Disparity in electron carriers is noticed at both the phases with +100 mV (dominantly direct electron transfer)/-100 mV (cytochrome components) potential as well as control (non-specific and multiple carriers) which signify alteration in electron transfer mechanism aligned with change in surface potential. Microbial community analysis depicted the enrichment of exo-electrogenic bacteria belonging to phylum Proteobacteria (Gram negative bacteria) dominant at −100 mV, while Firmicutes (Gram positive bacteria) at +100 mV and a mixed bacterial population at control. Electrochemical investigations correlated with biological efficiency of MFC, which discerns a way to comprehend the underlying electron transfer process triggered in response to change in anode potential.

Effects of the physical parameter on gate all around FET

As the devices are getting compact, the size of transistors reduces day by day; however, with certain limitations. Due to miniaturization, the characteristics of the transistor change due to quantum mechanical effects and the present scenario, analytically modeled surface potential-based gate all around (GAA) FET model by solving 1-D Poisson’s equation, approximation method and using necessary boundary condition. Here, the change in channel material (Si, InP, GaAs, InAs and Ge), channel radius (varied from 6 nm to 10 nm), oxide thickness (changed from 2 nm to 5 nm), drain to source voltage (varied from −0.5 V to 0.5 V), Source/Drain doping (varied from 1017 to 1022/cm3) and temperature (from 0 to 300 K) of the transistor, surface potential changes from −1.6 V to 1.3 V approx. respectively, considered as the GAA FET parameters. The proposed novel model exhibits better control over hot carrier effect, Drain Induced Barrier Lowering (DIBL), reduced threshold voltage and other such short channel effects in the GAA FET. Moreover, the I–V characteristics of the GAA FET were analyzed. The MATLAB code is used for modeling of the GAA FET nanowire transistor.

Illumination/Darkness-Induced Changes in Leaf Surface Potential Linked With Kinetics of Ion Fluxes.

A highly reproducible plant electrical signal–light-induced bioelectrogenesis (LIB) was obtained by means of periodic illumination/darkness stimulation of broad bean (Vicia faba L.) leaves. By stimulating the same position of the same leaf with different concentrations of NaCl, we observed that the amplitude and waveform of the LIB was correlated with the intensity of stimulation. This method allowed us to link dynamic ion fluxes induced by periodic illumination/darkness to salt stress. The self-referencing ion electrode technique was used to explore the ionic mechanisms of the LIB. Fluxes of H+, Ca2+, K+, and Cl− showed periodic changes under periodic illumination/darkness before and after 50 mM NaCl stimulation. Gray relational analysis was used to analyze correlations between each of these ions and LIB. The results showed that different ions are involved in surface potential changes at different stages under periodic illumination/darkness. The gray relational grade reflected the contribution of each ion to the change in surface potential at a certain time period. The ion fluxes data obtained under periodic illumination/darkness stimulation will contribute to the future development of a dynamic model for interpretation of electrophysiological events in plant cells.

Adsorption of sodium iodine at air/water interface

The change in surface potential was measured for NaI solutions. The modelled surface charge was then calculated and compared with molecular simulations. It was found that I− was enhanced at the air/water interface more than Na+. The result, which was confirmed by simulations, was opposite to the previous observation with NaCl. The trend is also consistent with anionic effects: larger and more polar anions adsorbed stronger at the air/water interface. The theoretical model was applied successfully to describe the changes for both systems, which are positive for NaCl and negative for NaI, respectively. The combined results of the two systems also revealed that the self-ionization of pure water induced a positive surface charge at 16.9 mV.

Electrochemical Reduction of Undoped and Cobalt-Doped BiFeO3 Induced by Water Exposure: Quantitative Determination of Reduction Potentials and Defect Energy Levels Using Photoelectron Spectroscopy.

The interaction of BiFeO3 and Co-doped BiFeO3 thin-film surfaces with water vapor is examined using photoelectron spectroscopy. Water exposure results in an upward shift of the Fermi energy, which is limited by the reduction of Bi and Fe in undoped BiFeO3 and by the reduction of Co in oxidized Co-doped BiFeO3. The results highlight the importance of surface potential changes induced by the interaction of solid surfaces with water and the ability of photoelectron spectroscopy to quantitatively determine electrochemical reduction potentials and defect energy levels.

Nano-morphology, crystallinity and surface potential of anatase on micro-arc oxidized titanium affect its protein adsorption, cell proliferation and cell differentiation.

Using a novel microwave-assisted hydrothermal (MW) process we created nano-scale anatase on micro-arc-oxidized (MAO) titanium surface. The morphology/crystallinity and surface potential of the anatase which altered by Ca/P ions concentrations and pH in the MW medium were characterized by atomic force microscopy, Kelvin probe force microscopy, Raman spectrometer, and x-ray photoelectron spectroscopy. The surface of MWDD (processed in DD water) and MWCP (in neutral pH medium with Ca/P ions) are covered with anatase spikes, which enhance their nano-roughness, hydrophilicity, and possess lower surface potential than other groups. The nano-precipitates on surface of MWCP9 and MWCP11 (processed in medium containing Ca/P ions at pH 9 or pH 11) were mainly amorphous anatase with less P ions. The protein adsorption of negatively charged bovine serum albumin was higher in MWDD and MWCP groups which possess lower surface potential. The adsorption of positively charged histones on the surface of MWCP11 was higher compared to the other groups. The osteogenic characterizations of D1 mice bone marrow mesenchymal stem cells co-cultured for 1, 7, and 14 days were measured by ALP and osteopontin assays. Although MW groups revealed comparable viability of D1 mice bone marrow mesenchymal stem cells to MAO group, their superior hydrophilicity and higher protein adsorption, thus regulating the differentiation of osteoprogenitor stem cells demonstrating higher ALP and osteopontin secretion after 7 days and 14 days. The nanoscale topography, crystallinity and surface potential change the hydrophilicity and protein adsorption on the MW treated titanium surface, thus regulating the differentiation of osteoprogenitor stem cells in vitro.

Effects of barrier thickness on carrier non-radiative relaxation process in InGaAs/GaAsP superlattice solar cells by piezoelectric photothermal and surface photovoltage spectroscopies

We investigated the carrier non-radiative relaxation process of InGaAs/GaAsP superlattice (SL) solar cells with different barrier thicknesses by combining piezoelectric photothermal (PPT) and surface photovoltage (SPV) measurements. The former technique detected heat generated by non-radiative relaxation and the latter detected the surface potential change induced by the carrier accumulation. Although the mechanisms of these measurements were different, corresponding signals of the transition between the quantum levels were observed in both spectra. The SPV signal intensities were independent of the barrier thicknesses. The carrier tunneling process functioned poorly under open-circuit conditions. Conversely, the PPT signal intensities increased with decreasing barrier thickness. We experimentally demonstrated that the non-radiative relaxation component increased as the barrier thicknesses decreased owing to the lattice relaxation at interfaces between the quantum well and barrier layers. We concluded that the non-radiative relaxation process in the SL structure must be directly evaluated to improve the solar cell performance.

CVD grown nitrogen doped graphene is an exceptional visible-light driven photocatalyst for surface catalytic reactions

The photocatalytic potential of large area CVD grown nitrogen doped graphene (NGr) has been explored though the chemical transformation of 4-nitrobenzene thiol into p,p′-dimercaptoazobenzene. Decoration of NGr with Ag nanocubes with rounded edges to form NGr/Ag nanohybrids resulted in a slight increase in the work-function and a decrease in the n-type character of NGr due to ground state transfer of negative charge from NGr to Ag. The Ag nanocubes exhibited a localized surface plasmon resonance (LSPR) at ~425 nm. When the NGr/Ag nanohybrids were illuminated with visible light of wavelength close to the LSPR peak, Kelvin probe force microscopy (KPFM) indicated a dramatic change in surface potential of −225 mV and Raman spectra detected electron accumulation in NGr, which are attributed to a high local field enhancement-mediated hot electron injection into NGr and the formation of long-lived charge separated states. Pristine nitrogen doped graphene and its coupled system with plasmonic Ag nanoparticles showed superior photocatalytic performance compared to bare plasmonic Ag catalyst. While standalone Ag NPs were unable to complete the transformation of 4-NBT into DMAB even at a laser power of 10 mW, NGr/Ag nanohybrids completed this transformation at a laser power of 1 mW, pointing to the high photoreduction strength of NGr/Ag. Density functional theory (DFT) based computational modeling was used to examine the electronic structure of graphene doped with graphitic, pyridinic and pyrrolic nitrogen dopant atoms. DFT results indicated an enhanced chemical reactivity of NGr due to stronger localization of charge at the dopant sites and a pronounced difference in the projected density of states (PDOS) for carbon atoms in proximity to, and distant from, the nitrogen dopant sites.

Traps induced Greens function based mathematical modeling for BaTiO3–SrTiO3 gate stack dual metal GAA MOSFET

In this paper, an analytical model has been developed to analyze the impact of trap charges on Dual Metal Gate-All-Around (DMGAA) MOSFET with BaTiO3–SrTiO3 epitaxial oxide layer as gate stack using Greens function and conformal mapping. Trap charges have been induced to observe the changes in surface potential, electric field and drain current. To further investigate the impact of trap charges the trap density is varied. This enhances the drain current with high ION/IOFF ratio. The analytical results so obtained are compared with the simulated data and are in good agreement thus validating the proposed model. It is also proposed that the device can offer high performance, low leakage power along with high gain and is perfect for analog RF applications. It can be concluded that proposed DMGAA MOSFET is a promising device and a suitable replacement for the existing conventional GAA MOSFETs.

Removal of model dyes on charged UF membranes: Experiment and simulation

Charged ultrafiltration (UF) membranes can repel electrically charged molecules that are smaller than the size of the membrane pores and display high rejection of solutes, high flux, and low operation pressures compared to uncharged UF, nanofiltration (NF) and reverse osmosis (RO). Here, a charged UF membrane composite (PANI/PVDF) was prepared and regulated via electrochemically reversible control in portions of amine/imine functional groups of PANI. As a result, the permeability and rejection ratios of CR2- on charged PANI/PVDF, with PVDF as a control, increased from 19.6 to a maximum of 183.3 L m-2 h-1 bar-1 and from 3.4% to 74%, which expands the trade-off confine benefited from surface potential change from-12.21 mV to-25.26 mV, furtherly, the rejection ratio of CR2- on PANI/PVDF reached up to 93% via the electrochemical regulation. Finally, a fixed-charge model was built that well describes the steric and electric repulsion effects on membrane performance and the important roles of the electrochemically controllable surface charge. Moreover, the contour map of rejection ratios containing the ratio of molecular size vs the average pore size of the membrane (r/R = 0.2-1.0) and the zeta potential (-10 to-60 mV) were taken into account, which can be used to visually understand the rejection performance of membranes. This model is also appropriate for varying molecular sizes and for molecules with different charges. Our work opens a new horizon for the design of electrochemically controllable charged membranes to remove charged compounds.

Effect of surface potential on corrosion behavior of the fusion boundary in the dissimilar welds between 316L stainless steels and Inconel 182 alloy

The microstructure, surface potential value and corrosion properties of fusion boundary in 316L stainless steel/Inconel 182 dissimilar welds were investigated. The results indicated that there were two different types of fusion boundaries alternately distributed in the dissimilar welds, and there was a large potential value difference between two sides of the fusion line in different types of fusion boundaries. The oxides and oxidation behavior of different types of fusion boundaries were strongly dependent on their surface potential value change on the fusion boundaries.

Direct evidence for grain boundary passivation in Cu(In,Ga)Se2 solar cells through alkali-fluoride post-deposition treatments

The properties and performance of polycrystalline materials depend critically on the properties of their grain boundaries. Polycrystalline photovoltaic materials – e.g. hybrid halide perovskites, copper indium gallium diselenide (CIGSe) and cadmium telluride – have already demonstrated high efficiencies and promise cost-effective electricity supply. For CIGSe-based solar cells, an efficiency above 23% has recently been achieved using an alkali-fluoride post-deposition treatment; however, its full impact and functional principle are not yet fully understood. Here, we show direct evidence for the passivation of grain boundaries in CIGSe treated with three different alkali-fluorides through a detailed study of the nanoscale optoelectronic properties. We determine a correlation of the surface potential change at grain boundaries with the open-circuit voltage, which is supported by numerical simulations. Our results suggest that heavier alkali elements might lead to better passivation by reducing the density of charged defects and increasing the formation of secondary phases at grain boundaries.

Semiconductor-Based Biosensor Functionalized with Jacalin for Detection of Secretory IgA in Sweat Sample

Recently, mental stress-related diseases, such as integration disorder syndrome and depression, affect people's health. Previously, the relation between concentration of stress-markers and mental stress condition has been reported, suggesting that a simple and daily detection of these markers from biological samples is important to prevent the disease. Secretory immunoglobulin A (s-IgA) which is present in the non-invasive biological samples, such as sweat or saliva, is one of the candidates to measure the mental stress. For the detection of s-IgA, field effect transistor (FET) biosensor is a promising device to easily and quickly detect biomolecules, as the FET characteristics can be responded to the change of surface potential caused by the adsorption of charged molecules. To achieve a sensitive detection by using FET biosensors, small receptors have been applied for an effective use of charge-recognition region, Debye length [1]. In this study, jacalin, a small tetrameric lectin from plant (66 kDa), was selected as a receptor to detect s-IgA. Each monomer of jacalin has a glycan-binding site to the hinge region of IgA, thus the sensitivity expected to be improved due to increasing the amounts of specifically adsorbed s-IgA. The SiO2 gate surface was exposed to O2 plasma (200 W for 1 min) in order to introduce hydroxyl groups reacting with triethoxysilane groups of self-assembled monolayer (SAM). Then, FET was immersed in 1%(v/w) 3-aminopropyltriethoxysilane toluene solution at 60ºC for 7 min in an argon atmosphere, followed by the cross-linking by glutaraldehyde. After the modification with the cross-linker, jacalin was immobilized on FET gate surfaces, and ethanolamine capping was performed to prevent the non-specific adsorption of contaminating molecules. The electrical responses were calculated by the FET characteristics before and after the addition of target solution. The FET characteristics were measured by sweeping the gate-voltage from -2.0 V to 0 V with 0.1 V drain voltage in 0.01 × phosphate buffered saline (pH 7.4). The immobilization of jacalin through the aminopropylsilane SAM was confirmed from atomic force microscopic images on the surface morphology change of the FET gate surfaces. Additionally, to optimize the immobilization condition, the relationship between concentration of jacalin solution and magnitudes of electrical responses were examined. Then, the specificity of jacalin-immobilized FET biosensor to s-IgA were confirmed by the comparison of responses caused by the addition of s-IgA and human serum albumin (HSA). The ΔV g was shifted in a positive direction due to the negative charges of s-IgA (isoelectric point = 4.5-5.0). On the other hand, when the HSA was added to the FET biosensor, the responses was scarcely observed, suggesting that the jacalin-immobilized surface specifically captured the s-IgA (Figure 1). In addition, a correlation between the FET responses and s-IgA from 100 ng/mL to 100 μg/mL, including the fluctuations of concentration in human sweat sample, was clearly obtained. These results suggested that jacalin could be useful as a receptor for FET biosensors to achieve a simple and sensitive detection of s-IgA. [1] S. Cheng, K. Hotani, S. Hideshima, S. Kuroiwa, T. Nakanishi, M. Hashimoto, Y. Mori and T. Osaka, Materials, 7, (4), 2490-2500, (2014). Figure 1

An Electrophysiological Approach to Measure Changes in the Membrane Surface Potential in Real Time

Biological membranes carry fixed charges at their surfaces. These arise primarily from phospholipid headgroups. In addition, membrane proteins contribute to the surface potential with their charged residues. Membrane lipids are asymmetrically distributed. Because of this asymmetry, the net-negative charge at the inner leaflet exceeds that at the outer leaflet. Changes in surface potential are predicted to give rise to apparent changes in membrane capacitance. Here, we show that it is possible to detect changes in surface potential by an electrophysiological approach; the analysis of cellular currents relies on assuming that the electrical properties of a cell are faithfully described by a three-element circuit (i.e., the minimal equivalent circuit) comprised of two resistors and one capacitor. However, to account for changes in surface potential, it is necessary to add a battery to this circuit connected in series with the capacitor. This extended circuit model predicts that the current response to a square-wave voltage pulse harbors information, which allows for separating the changes in surface potential from a true capacitance change. We interrogated our model by investigating changes in the capacitance induced by ligand binding to the serotonin transporter and to the glycine transporters (GlyT1 and GlyT2). The experimental observations were consistent with the predictions of the extended circuit. We conclude that ligand-induced changes in surface potential (reflecting the binding event) and in true membrane capacitance (reflecting the concomitant conformational change) can be detected in real time even in instances in which they occur simultaneously.

Sensitivity Improvement of Medical Dosimeters Using Solution Processed TIPS-Pentacene FETs

In this paper, we have explored the electrical and material properties of TIPS-Pentacene for low doses of gamma irradiation. Interface trap/defect generation was studied post gamma irradiation of TIPS-Pentacene transistors. This paper demonstrates that the traps/defects at the bulk/surface of TIPS-Pentacene and SiO2/Si interface states significantly influence the sensing behavior. It is demonstrated that the interface trap charges introduced by the gamma radiation are significant in the TIPS-Pentacene thin-film instead of the SiO2/Si. The detector exhibits a record high sensitivity of ~3 V/Gy at 1 Gy in ambient air. A theoretical model was developed to understand the change in ON-current and channel doping. The change in surface potential of film was studied by Kelvin probe force microscopy (KPFM). Developed model was in good agreement with the KPFM results. These promising results indicate that our device can be used as a dosimeter for medical applications with high sensitivity.

Imaging the surface potential at the steps on the rutile TiO2(110) surface by Kelvin probe force microscopy.

Although step structures have generally been considered to be active sites, their role on a TiO2 surface in catalytic reactions is poorly understood. In this study, we measured the contact potential difference around the steps on a rutile TiO2(110)-(1 × 1) surface with O2 exposure using Kelvin probe force microscopy. A drop in contact potential difference was observed at the steps, indicating that the work function locally decreased. Moreover, for the first time, we found that the drop in contact potential difference at a <1−11> step was larger than that at a <001> step. We propose a model for interpreting the surface potential at the steps by combining the upward dipole moment, in analogy to the Smoluchowski effect, and the local dipole moment of surface atoms. This local change in surface potential provides insight into the important role of the steps in the catalytic reaction.

Enhanced photo-stability of inverted organic solar cells via using polyethylenimine in the electron extraction layers

Abstract The influence of using Polyethylenimine (PEI) in the electron extraction layers (EELs) on the photo-stability of inverted organic solar cells (OSCs) is investigated. Results show that introducing PEI in the commonly used ZnO EELs, either mixed in the same layer with the ZnO (ZnO:PEI mixture) or in a separate layer in the form of a bilayer EEL configuration (ZnO/PEI), reduces the susceptibility of OSCs to photo-degradation with the mixture giving more significant stability enhancements. In comparison to the widely used ZnO EEL, the use of ZnO:PEI mixture is found to lead to ∼ 5× higher PCE stability under continuous UV irradiation, the latter being the main factor behind the limited stability of the cells under sunlight, primarily due to a more stable V o c and FF. Tests on electron only devices show that the higher photo-stability is mainly due to the role of the ZnO:PEI mixture in minimizing light-induced deterioration in electron collection efficiency at OSCs electron collection contacts under sunlight. Kelvin probe force microscopy (KPFM) measurements show that the use of ZnO:PEI helps maintain a more stable surface potential at the electron collection contact, hence the more stable V o c and FF. X-ray photoelectron spectroscopy (XPS) measurements reveal that the stability enhancement is likely associated with chemical interactions between PEI and ITO at the ITO/ZnO:PEI interface that produce a more electronically and energetically stable contact that is less susceptible to changes in surface potential or work function by UV illumination. Using PEI in the form of a neat layer next to the ITO in a bilayer EEL (PEI/ZnO) is found to provide a similar significant enhancement in photo-stability, further ascertaining the above conclusions. The findings not only reveal the potential of utilizing PEI in the EEL, but also shed light on some of the root causes of the limited photo-stability of OSCs and approaches to mitigate their effect.