The critical role of grain boundaries for (CH(NH2)2PbI3)0.85(CH3NH3PbBr3)0.15 perovskite solar cells studied by Kelvin probe force microscopy under bias voltage and illumination is reported. Ion ...migration is enhanced at the grain boundaries. Under illumination, the light‐induced potential causes ion migration leading to a rearranged ion distribution. Such a distribution favors photogenerated charge‐carrier collection at the grain boundaries.
Surface properties of superprotonic (K1-х(NH4)x)3H(SO4)2 (x ≥ 0.57) single crystals and their evolution under humidity were studied by optical polarization microscopy, scanning electron microscopy ...(SEM), and energy-dispersive X-ray spectroscopy (EDXS). Traditional method of atomic force microscopy (AFM) and sophisticated methods such as Kelvin probe force microscopy (KPFM) and scanning capacitance force microscopy (SCFM) were also used. Fresh and aged cleavage surfaces perpendicular and parallel to the c axis of the trigonal superprotonic phase were examined. The effect of air humidity on the surface morphology, surface conductivity, surface potential and surface capacitance was studied. The influence of material composition and surface orientation was considered. During ageing for 430 h, the (001) sample surfaces, initially stepped, were smoothened, surface electric potential changed from negative greater than a hundred of millivolts in absolute value to positive of about 80 mV, and a modified layer containing new crystal phases was formed.
•Superprotonic phases (K1-x(NH4)x)3H(SO4)2 (x ≥ 0.57) are stabilized at room temperature and demonstrate high proton conductivity.•Their surface properties were studied by AFM. C-AFM, KPFM, SCFM, optical and electron microscopy, and structural analysis.•Local CVCs have shown that conductivity is anisotropic and is due to the composition and structure of superprotonic phases.•Based on morphological data, the stability of the surface of samples of different composition to humidity was assessed.•The formation of a modified layer with new phases on the crystal surface during prolonged exposure under humidity is shown.
CH3NH3PbI3-based solar cells were characterized with electron beam-induced current (EBIC) and compared to CH3NH3PbI3–x Cl x ones. A spatial map of charge separation efficiency in working cells shows ...p-i-n structures for both thin film cells. Effective diffusion lengths, L D, (from EBIC profile) show that holes are extracted significantly more efficiently than electrons in CH3NH3PbI3, explaining why CH3NH3PbI3-based cells require mesoporous electron conductors, while CH3NH3PbI3–x Cl x ones, where L D values are comparable for both charge types, do not.
The measurement of electrical surface charges and their associated potentials at the nanoscale plays a crucial role in understanding important molecular processes, such as corrosion or biological ...tissue interactions. Measurement of these potential distributions, especially in aqueous environments, is not always possible with standard AFM-based techniques. The herein proposed single-harmonic response open-loop Kelvin-probe Force Microscopy (SH-KPFM) mode circumvents issues of common methods and enables such investigations in water via a suitable choice of the electrical excitation signal. The mode is validated by means of parameter sweeps on calibration samples and compared to conventional KPFM in air. Furthermore, SH-KPFM is applied to investigate the potential distribution and time-dependent depolarization of a charged PMMA surface immersed in deionized water, demonstrating its ability to analyze complex electrostatic interactions on the nanoscale.
Copper (Cu) is present not only in the electrode for inverted-structure halide perovskite solar cells (PSCs) but also in transport layers such as copper iodide (CuI), copper thiocyanate (CuSCN), and ...copper phthalocyanine (CuPc) alternatives to spiro-OMeTAD due to their improved thermal stability. While Cu or Cu-incorporated materials have been effectively utilized in halide perovskites, there is a lack of thorough investigation on the direct reaction between Cu and a perovskite under thermal stress. In this study, we investigated the thermal reaction between Cu and a perovskite as well as the degradation mechanism by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Kelvin probe force microscopy (KPFM). The results show that high temperatures of 100 °C induce Cu to be incorporated into the perovskite lattice by forming “Cu-rich yet organic A-site-poor” perovskites, (Cu x A1–x )PbX3, near the grain boundaries, which result in device performance degradation.
Elegant Z-scheme WO3/Au/In2S3 nanowire arrays were precisely constructed through a facile step-by-step route. Surface potential change on pristine or In2S3–Au coated WO3 single nanowire under dark ...and illumination detected through a Kelvin probe force microscopy (KPFM) technique indicates that the vectorial holes transfer of In2S3 → Au → WO3 should occur upon the excitation of both WO3 and In2S3. In such charge transfer processes, the embedded Au nanoparticles in the heterojunction systems act as a charge mediator for electrons in the conduction band of WO3 and holes in the valence band of In2S3. The strong charge carrier separation ability of this structure will finally enhance the oxidation ability of WO3 with high concertation of photogenerated holes and, further, leave the free electrons in the In2S3 with long surviving time. Therefore, the unique Z-scheme WO3/Au/In2S3 heterostructure shows great visible-light activity toward photocatalytic reduction of CO2 in the presence of water vapor into renewable hydrocarbon fuel (methane: CH4).
Despite the rapid progress in organic–inorganic halide perovskites (OIHPs) for applications such as solar cells and detectors, knowledge of coupling between electronic and ionic charge carrier ...dynamics is so far limited. While the presence of dual-conduction channels is widely accepted, the precise physical mechanisms governing the impact of electronic (e.g. electrons and holes) and ionic conduction, especially interface phenomena, remain uncertain. The lack of understanding stems largely from the lack of appropriate tools to capture the electrochemical dynamics on the length scales of the local inhomogeneities present (e.g., interfaces, grain boundaries, space charge regions) and time scales over which the coupled dynamics take place. Here, we implement Kelvin probe force microscopy (KPFM) to explore the charge carrier dynamics at the methylammonium lead tribromide (MAPbBr3) single crystal–gold electrode interface. In this work, the temporal dynamics of the electric field and charge carrier distribution at the electrode interface is spatially visualized by time-resolved KPFM mapping. The results demonstrate an interplay of several phenomena, including charge injection, recombination, and ion migration, leading to an unbalanced charge dynamic at MAPbBr3 single crystal–electrode interface under forward and reverse bias conditions explaining the origin of the current–voltage hysteresis in these devices. We contrast the bias-assisted charge dynamics under both illuminated and dark conditions, providing a comprehensive picture of overall carrier dynamics and interface properties in a MAPbBr3 single crystal with lateral symmetric Au electrodes. Remarkably, illumination leads to the formation of a wider space charge region due to accumulation of negative charges (both electrons and halide ions) at the positive electrode, which can effectively screen the external electric field leading to lower charge extraction efficiency. The results suggest that the choice of contact or interfacial engineering can control the performance of OIHP devices without requiring modification of the material’s bulk properties.
The aggravating extreme climate changes and natural disasters stimulate the exploration of low‐carbon/zero‐carbon alternatives to traditional carbon‐based fossil fuels. Solar‐to‐hydrogen (STH) ...transformation is considered as appealing route to convert renewable solar energy into carbon‐free hydrogen. Restricted by the low efficiency and high cost of noble metal cocatalysts, high‐performance and cost‐effective photocatalysts are required to realize the realistic STH transformation. Herein, the 2D FePS3 (FPS) nanosheets anchored with TiO2 nanoparticles (TiO2/FePS3) are synthesized and tested for the photocatalytic hydrogen evolution reaction. With the integration of FPS, the photocatalytic H2‐evolution rate on TiO2/FePS3 is radically increased by ≈1686%, much faster than that of TiO2 alone. The origin of the greatly raised activity is revealed by theoretical calculations and various advanced characterizations, such as transient‐state photoluminescence spectroscopy/surface photovoltage spectroscopy, in situ atomic force microscopy combined with Kelvin probe force microscopy (AFM‐KPFM), in situ X‐ray photoelectron spectroscopy (XPS), and synchrotron‐based X‐ray absorption near edge structure. Especially, the in situ AFM‐KPFM and in situ XPS together confirm the electron transport pathway in TiO2/FePS3 with light illumination, unveiling the efficient separation/transfer of charge carrier in TiO2/FePS3 step‐scheme heterojunction. This work sheds light on designing and fabricating novel 2D material‐based S‐scheme heterojunctions in photocatalysis.
Anchoring of TiO2 nanoparticles onto FePS3 nanosheets creates S‐scheme n‐p heterojunction of TiO2/FePS3 with a strong built‐in electric field, significantly raising the photocatalytic hydrogen evolution rate. Atomic force microscopy Kelvin probe force microscopy and X‐ray photoelectron spectroscopy confirm the photogenerated charge transfer pathway, corroborating the formation of a TiO2/FePS3 S‐scheme heterojunction with efficient charge separation and transfer.
Herein, we report on an air-processed high performance self-powered hybrid perovskite (Pe) photodetector with plasmonic Silver nanoparticle (Ag NP) embedded hole-transport-layer (HTL), without the ...use of any electron-transporting layer (ETL). It is demonstrated that in the absence of ETL in the device, the Ag NPs embedded PEDOT:PSS HTL improves the photodetection performance significantly. We used a novel N2 gas assisted fast crystallization method for the deposition of perovskite film in ambient condition to form uniform Pe layer as compared to the nonuniform film obtained in conventional deposition method. The Pe film on Ag NPs embedded PEDOT:PSS layer shows enhanced optical absorption in the UV–visible region due to the plasmonic absorption by the Ag NPs. At zero bias, the ETL-free Ag NPs-Pe hybrid device shows ∼45% enhanced responsivity and ∼3 times faster photoresponse compared to the pristine device. The enhancements in the performance of hybrid photodetector are attributed to plasmon-enhanced optical absorption and hot electron generation, as well as improvement in charge extraction and transport by Ag NPs, which are corroborated by steady-state and time-resolved photoluminescence measurements. Impedance analysis of the devices shows the reduced carrier transfer resistance of the hybrid device, which results in superior transport of photo-generated charge carriers. Direct evidence for the increase in the work function by ∼47 meV for Ag NPs doped PEDOT:PSS film is provided from the Kelvin probe force microscopy analysis. This increase in work function enables favorable band alignment with reduced energy barrier and a superior carrier transport resulting in improved photodetection performance for the hybrid device. Our results are significant for the development of high-performance, low-cost, ETL free plasmonic perovskite photodetectors for futuristic applications.
Self-powered electron-transport-layer-free perovskite fast photodetector with plasmonics enabled hole-transport-layer using a modified perovskite deposition method in ambient air. Display omitted
•Air processed high performance self-powered hybrid perovskite photodetector with plasmonic Ag nanoparticle embedded hole-transport-layer.•A novel N2 gas assisted fast crystallization method for the deposition of high quality uniform perovskite film in ambient condition.•Enhanced performance is due to plasmonic absorption, hot electron generation and improved charge extraction and transport by Ag NPs.•Direct evidence for the increase in the work function of Ag NP embedded PEDOT:PSS film is provided from the Kelvin probe force microscopy.
Contact electrification (CE) (or triboelectrification) is a well‐known phenomenon, and the identity of the charge carriers and their transfer mechanism have been discussed for decades. Recently, the ...species of transferred charges in the CE between a metal and a ceramic was revealed as electron transfer and its subsequent release is dominated by the thermionic emission process. Here, the release of CE‐induced electrostatic charges on a dielectric surface under photon excitation is studied by varying the light intensity and wavelength, but under no significant raise in temperature. The results suggest that there exists a threshold photon energy for releasing the triboelectric charges from the surface, which is 4.1 eV (light wavelength at 300 nm) for SiO2 and 3.4 eV (light wavelength at 360 nm) for PVC; photons with energy smaller than this cannot effectively excite the surface electrostatic charges. This process is attributed to the photoelectron emission of the charges trapped in the surface states of the dielectric material. Further, a photoelectron emission model is proposed to describe light‐induced charge decay on a dielectric surface. The findings provide an additional strong evidence about the electron transfer process in the CE between metals and dielectrics as well as polymers.
The decay of contact electrification (CE)‐induced electrostatic charges under light irradiation is investigated at the nanoscale. The results suggest that there exists a threshold photon energy for releasing the triboelectric charges from the surface, and the charge decay is suggested to be caused by photoemission. The photon excitation effect provides strong evidence for electron transfer in CE.
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