Spray‐Coated Inorganic Lead‐Free Double Perovskite Cs2AgBiBr6 Based Large‐Scale Triboelectric Nanogenerator for Enhanced Energy Harvesting

Low‐cost and efficient large‐scale triboelectric nanogenerator (TENG) is considered as the new scheme for distributed mechanical conversion or renewable energy utilization. An extremely popular all‐inorganic lead‐free double perovskite Cs2AgBiBr6 (CABB) has emerged as extraordinary potential material in triboelectric semiconductors’ substitution, overcoming high‐impedance limitations associated with organic‐polymer‐insulator based materials. In this study, assembled by the certified available positive frictional material CABB, TENG with sandwiched structure of ITO/compact‐TiO2/mesoporous‐TiO2/CABB – the poly‐tetra‐fluoroethylene/Al exhibits appropriate performance on environmental stability and output capacity for which structure can impede charges decay. Fabrication process comparison shows that as an inexpensive large‐scale functional films preparation method, sprayed CABB TENG with brilliant relative dielectric constant and work function difference possess more distinguished output characteristics. This is confirmed by higher open‐circuit voltage of 105 V, larger short‐current density of 2.45 mA m−2 at 0.25 Hz motion parameter, and more abundant output power density of 0.76 W m−2 under 10 Hz. Further study confirms that both higher frequency and larger contact‐area are conducive to total output power, while terminal charging speed is inversely or positively proportional with capacitance or mechanical frequency. Final physical display effect of sprayed CABB TENG lights up at least 53 commercial yellow‐LEDs, holding decent energy conversion ability.


Introduction
Since triboelectric nanogenerator (TENG) structure concept was first raised by Wang's group [1] in 2012, it has attracted widespread attention and has been offered significant application potentials in various fields such as self-powered sensors, [2,3] medical therapies, [4] artificial intelligence, [5] and Internet of things (loTs) [6] for its excellent energy conversion characterization.As an emerging eco-friendly energy-harvesting system, TENG provides an efficient mechanical energytransformation mode that can convert distributed low-frequency mechanical energy, such as water wave, [7] wind energy, [8] or body motion [9] into electrical energy by utilizing the coupling of contact electrification and electrostatic induction effects [10] based on the chargeretention capability and work function (W f ) difference between two frictional materials.However, though with highly negative charge storing capability, the practicality and popularity of these traditionally used dielectric frictional polymer materials are usually limited due to their inherent low current density output. [11]To address these challenges, the integration of semiconductors [12] with competitive electronic conductivity into TENGs becomes an outstanding approach for robust TENG formation.These schemes can facilitate charge transition thereby optimizing electrical output performances.For example, gallium nitride (GaN)-based semiconductor direct-current TENGs [13] (SDC-TENGs) were recently investigated to explore the carrier transport mechanism.The maximum voltage of the studied device reached 25 V for lighting up a series of LEDs.A gallium nitride/silicon (GaN/Si) heterojunction [14] could also achieve a maximum DC voltage of 130 V, with simultaneous peak power density of 2.8 W m −2 .
As the most promising semiconductor, perovskite-like materials with the structure of ABX 3 [15] or A 2 B I + B II 3+ X 6 [16,17] are widely used in the areas such as photovoltaics, [18] photo-detectors, [19] display [20] and light-emitting diodes [21] due to their remarkable optoelectronic properties.Moreso, in accordance with their piezoelectric and dielectric properties, perovskite-based piezoelectric nanogenerators (PENGs) and TENGs have been successively proposed.Su. et al. reported the first photoinduced enhancement of perovskite TENG [22] based on MAPbI 3 with a combination of photoelectricity and triboelectricity that reached a peak voltage of 15.3 V in the absence of illumination and 17 V upon irradiation with light source.Tang group has also made great progress on CsPbX 3 TENG whose output power density was [23] approximately up to 3.04 W m −2 generated by promoted build-in electric field, while adjusting Fermi level (E F ) through ion doping [24] is indeed a feasible strategy to increase corresponding performance mentioned above to 3.07 W m −2 .Furthermore, this CsPb x Ba 1-x Br 3 TENG could continuously light up over 80 commercial LED devices.Semiconductor-based TENG utilizes electron-ion coupling mechanism [25] to construct stable nanogenerator, [26] which combines electrostatic induction with ionic coupling and ensures a stable output in complex environments.Considering the toxicity of lead and instability of hybrid perovskite (MA + , FA + ), [16,27] inorganic lead-free double perovskite Cs 2 AgBiBr 6 (CABB) with highly dielectric constant [16] has absolute prospect in power generation while also maintaining device reliability under atmospheric conditions and safeguarding the investigator's health.Furthermore, the preparation method of high-quality and large-area TENG films has also attracted researchers' attention as well.Under normal circumstances, semiconductor layers of TENG are usually fabricated through blade technique, [28] dipping method, [29] spin-coating, [24] rolling method [30] et.al, and the polymer layers are usually purchased or synthesized by phase inversion method [28] and so on.An all-fibrous TENG [31] has been prepared by Xu. et al. using a one-step solution blow spinning technology.Similarly, Peng.et al. utilized a melt blowing technology to prepare large-size PP-NWF films. [32]This group also prepared large-area sandwiched CNTs/PP films [33] using co-extrusion blow film molding method afterward.Low-cost and large-area semiconductor films manufactured with spraying method [34] exhibit a great potential at uniform and stable TENG preparation, being expected to be applied in this experiment.
In this work, vertical contact-separation CABB TENGs were initially prepared, comprehensively studied for their triboelectric behaviors, charge mechanism, and triboelectric charge polarities with a sandwiched structure of ITO/c-TiO 2 (compact TiO 2 )/m-TiO 2 (mesoporous TiO 2 )/CABB -the poly tetra fluoroethylene (PTFE)/Al.As an inorganic crystallographic structure semiconductor, CABB TENG have absolute advantage in atmospheric stabilization at the lattice structure compared with organo-inorganic hybrid halide perovskite, which could work continuously under environmental conditions.Through exploring the polarity of CABB TENG, CABB locates between polyimide (PI) and fluorinated ethylene propylene (FEP), and could be regarded as a representative positive triboelectric material when equipped with PTFE.Using a low-cost and convenient scheme, stable and uniform large area CABB TENG obtained with spraying method usually demonstrates distinguished output characteristics, which derive from prominent relative dielectric constant and W f difference under theoretical analysis.Subsequent experimental praxis that open-circuit voltage (V oc ) of sprayed and spin-coated films were 105 and 51 V.A short-current density (J sc ) of 2.45 and 0.9 mA m −2 were obtained under 0.25 Hz mechanical motion frequency, which also confirms the inferred conclusion.Moreso, a higher frequency and larger contact area contribute to better V oc and I sc , being beneficial for the total output power.Rectifier output indicates that to store same electricity, swifter charging speed relies on smaller capacitance and larger mechanical frequency, while sprayed film possesses superior charge collection capability as expected.Ultimately, at least 53 commercial yellow LEDs were switched on and the maximum power density of sprayed CABB TENG is achieved at 0.76 W m −2 when using 10 Hz motor frequency.Therefore, fabricating TENGs with all-inorganic lead-free double perovskite CABB friction layer is a momentous enabling step toward achieving semiconductor-based TENGs, as well as a practicable route to obtain highly output performance TENGs.

Results and Discussion
In the vertical contact-separation CABB TENG mode, CABB and PTFE usually play the role of positive and negative triboelectric materials, respectively, for their different electron-binding capabilities, where PTFE accepts electrons and CABB donates electrons.Figure 1a demonstrates this CABB TENG device with a sandwiched structure of ITO/c-TiO 2 /m-TiO 2 /CABB -PTFE/Al.The positive triboelectric material structure is illustrated in Figure 1b and its actual cross-sectional structure is presented in Figure 1c.It is observable from Figure 1c that the sprayed film is much denser and more homogeneous than the spin-coated one where many agglomerates were formed [35] and crystal growth has been impeded for the fast crystallization process induced by fast solvent evaporation that appeared during a spin-coated procedure.The cross-sectional scales are presented in Figure S1 (Supporting Information).As shown in the schematic diagrams of Figure 1d,f, the TiO 2 layer, including c-TiO 2 and m-TiO 2 , was made on ITO glass substrate through spin-coated process, while inorganic lead-free CABB double perovskite film is fabricated next through a vapor assisted annealing method [36] or spraying method. [37]Considering the low solubility of CsBr in DMSO, high concentration CABB solution of 0.5m is usually synthesized through redissolving CABB crystals that are fabricated by a cooling crystallization method as reported by previous studies [16,27] in DMSO.In addition, preheated ITO glasses contribute to  an improved grain size [38] of CABB films.For comparation, untreated spin-coated film is shown in Figure S2 (Supporting Information).The surface structures of low-temperature sol-gel compact TiO 2 , mesoporous TiO 2 nanoparticles, and CABB films are presented in Figure 1e 1 ,e 2 ,g,h.The grain size of CABB layer is mainly focused on 626 or 211 nm by spin-coated or sprayed film respectively.Corresponding AFM pictures in Figure S3 (Supporting Information) also showed the roughness of each film.As an important parameter for the measurement of the surface state, the surface roughness (measured by the root mean square value, RMS) data characterized by AFM elucidates that sprayed film [39] with lower undulation has more effective contact area when a contact-separation TENG works, causing an improved triboelectric charge density.
As indicated in Figure 2a, XRD analysis of CABB films were carried out for characterizing its crystallographic structures.CABB possesses a perovskite-like structure through the substi-tution of Pb 2+ by Bi 3+ and Ag + , and the schematic structure is shown in the inset of Figure 2a.In addition, the XRD of the sprayed film, spin-coated film, and the simulated XRD are illustrated in the same diagram, whose diffraction pattern showed that peak positions exactly matched the CABB standard cubic elpasolite structure as the cell unit parameter is refined to a = 11.2640(8)Å with the space group Fm-3m.High annealing temperature at 285 °C facilitates the crystal pure phase formation of the CABB. Figure 2b-f present some basic properties of the films.Figure 2b,c are the UV-vis absorption and photoluminescence (PL) spectra of spin-coated and sprayed film.Absorption cutoff wavelength of spin-coated and sprayed film are 612 and 524 nm, whereas the bandgap energies are 2.03 and 2.37 eV respectively, and are within the range of former studies. [40,41]The peak positions in the both PL spectra are around 640 nm, where the large existing Stokes shift compared with its absorption spectrum suggests a strong electron-phonon coupling effect [42] within CABB double perovskite.Figure 2d estimates CABB films fluorescence lifetime () information subsequently, where fluorescence spectrometer is adjusted to a microsecond flashlamp (us lamp) mode that covers whole microsecond time scales.Through exponential fit, fast decay time of spin-coated and sprayed films are at 158 and 258 ns, while slow decay time are at 667 and 780 ns.Generally speaking, double exponential decay model in time-resolved PL (TRPL) shows the information about trap state and carrierrelated radiative recombination, which characterizes the material purity and lattice defects as well.Where the fast lifetime component  1 arises from the quenching of charge carriers at the surface, while the relatively slow decay lifetime  2 is attribute to the trap-induced nonradiative recombination in bulk perovskite. [43]rolonged carrier lifetime in sprayed film indicates the decreased trap-state density at the surface and the suppression of trapassisted nonradiative recombination in perovskite film meanwhile, which means that sprayed film with fewer defects and denser surface is more efficient for the extraction and transport of surface friction charges.A mobility and trap density calculation through SCLC (space-charge-limited bulk conduction) method are clarified in Figure 2e,f, where n Measured trap density of spin-coated and sprayed films are 3.68 × 10 15 and 1.28 × 10 14 cm −3 respectively, while the mobility were 1.09 × 10 −5 and 3.49 × 10 −4 cm 2 V −1 s −1 .The phenomenon of defect reduction and mobility improvement arises from the fact that sprayed [39] CABB films are more compact and smooth, have a better carrier transport capacity due to a full contact area.This displays a preponderance on carrier transportation as the AFM picture in Figure S3 (Supporting Information) depicts.What's more, corresponding surface potential data in Figure 2g,h also proves that sprayed film with high-quality surface possesses more stable surface potential at 0.43 V, while spincoated film is 0.38 V for which is affected by the surrounding surface fluctuations.Sprayed surface with higher potential is also beneficial to improve its output characteristics.Figure 2i portrays the significant influence factor of TENGs' electrical output characteristics about the relative dielectric constant ( r ).By measuring the capacitance-frequency at dark, where the frequency range covers from 10 to 10MHz, parameter  r is figured out through a parallel plate capacitor model: where C is the measured capacitor, S is the electrode area and D is the samples thickness.The  r of CABB SC is 48, as shown in the inset of Figure 2i, which is also comparable to previous studies. [16,41,44]Simultaneously,  r of spin-coated and sprayed films were 9.2 and 11.6 respectively under higher frequency above 10 6 Hz.Compared with some commonly used dielectric materials, such as PTFE [45] at 2.0-2.1, the polyvinylidene difluoride (PVDF) [46] at 6-8, the polyethylene glycol terephthalate (PET) [47] at 3-4, [48] inorganic lead-free double perovskite CABB composes the splendid semiconductor dielectric films provided with severalfold higher dielectric constant.Through comprehensive discussion of factors affecting dielectric polarization of CABB films, [49][50][51] the most profound element is probably the electrostatic potential gradient appearance within CABB film where inhomogeneous distribution of space charge is mainly caused by charge carrier migration over a material macroscopic dimension.Besides, the transfer of charge density, [23,50] which could promote larger open-circuit voltage (V oc ) output, is also positively affected by  r .This was later confirmed by experimental results that sprayed CABB film manifests substantially enhanced space charge polarization than spin-coated film.
Figure 3 mainly explains the working principle of vertical contact-separation mode of CABB TENG.Based on triboelectric and electrostatic induction effect coupling, Figure 3a-d elaborates device action, namely the triboelectricity generation process, during a "press-release" working period.In the initial state, no voltage applies and no current flows for there are no charges on both CABB side or PTFE surface when they are wide apart.CABB and PTFE start to be polarized, thereby loosing and gaining charges respectively in accordance with the triboelectric effects, until contact appears even compresses tightly between them by external forces.In the next step after their separation, triboelectric charges are induced on electrodes, and external voltage signals are subsequently generated.With "press-release" or "contact-separation" movement exists, periodic signals remain continuously.Finite element analysis software COMSOL Multiphysics also interprets the working procedure on vertical contactseparation mode TENG intuitionally through ideally electric potential distributing simulation in Figure 3e,f.Contact area of the device is set to be 2 cm × 2 cm and thickness of both CABB layer and PTFE film are 2 um and 50 um.As the "release" process proceeds, electric potential between triboelectric materials increases gradually since CABB and PTFE with opposite polarity have different charges on its surface.As the electricity mechanism declared in Figure 3a-d,g-j elucidate electron transfer principle at microcosmic level.Under normal circumstances, the contact triboelectrification between friction materials derives from W f difference. [51,52]Figure 3h introduces effective band energy structure of this device.Unpolarized CABB films' band energy data, W f and valence band (VB) energy are achieved through UVvis absorption analysis in Figure 2b,c and ultraviolet photoelectron spectroscopy (UPS) analysis in Figure 3g, where Figure 3g 0g 2 are the ups, W f and VB energy spectra separately.CABB films' W f are 4.69 and 4.11 eV, and the homologous VB energy are 1.57and 1.62 eV under spin-coated or sprayed fabrication.Differential preparation methods cause CABB surface state (defects, dislocations) being capable of storing electrons variation, leading to W f offset [53] further.Comprehensive information of TiO 2 [54]   and PTFE [55] band energy structure were obtained from previous studies.The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) play the role of valence band and conduction band as well as the chemical potential represents the E F in PTFE for accuracies of organic polymer. [56,57]s specified in Figure 3h, W f difference between CABB and PTFE is almost at 1.61 or 2.19 eV, promoting electron escape from CABB's orbital to PTFE's and leading to the band bend even achieving E F equilibrium as Figure 3j points.Notably, due to distinct W f between diverse films, sprayed films with higher W f exhibit distinguished output capacities than spin-coated for larger W f difference [58] would result in easier electron transition and enhanced output performance, being verified in Figure 4 and having the same conclusion as the obtained Figure 2f.Moreover, c-TiO 2 here serves as a hole-blocking layer that impedes the surface holes decay [59] from CABB suface to ITO electrodes, while the m-TiO 2 nanoparticles serve as the skeleton to construct a bulk heterojunction with CABB which contributes to the expansion of the specific surface area when contact separation occurs.However, TiO 2 thickness influence is also discussed in Figures S4 and  S5 (Supporting Information), indicating that spin-coated CABB film with proper TiO 2 thickness of 0.38 um and sprayed CABB film with TiO 2 thickness at 0.45 um possesses better output characteristics for its suitable electron transmission and trapping.
To keep E F under equilibrium, Figure 3i presents the bending energy band structure between TiO 2 and CABB, where sprayed CABB film has a larger hole barrier that contributes to impeding the carriers decay.Figure 3j describes carriers transition process in detail with polymer or conductive material as frictional layer.Conductive side like metal or ITO (W fm < W fs ) tends to drain electrons, negatively charging CABB surface.The electrons with higher E F will flow from metal to semiconductor due to the E F difference when metal-semiconductor contacts [60] at initial state.When relative motion appears, the nonequilibrium carriers generated by friction energy, and the surface state electrons that jumps to a higher energy level due to achieving friction energy that results to the charge flowing through interface to external circuit.Polymer with high charge binding capacity emerges the opposite.Considering the existence of surface/defects states in the band gap of dielectric materials caused by its surface symmetry breaking, [61] dielectrics VB below semiconductor E F will induce the charge to fill the surface states of dielectric materials in its bandgap, which is formed by electrons transferring from semiconductor into dielectrics, resulting in overall negative charges on the dielectric surface.Such electrons will not transfer back to semiconductor surface even to the separation, for they are surface-state-bound charges and cannot flow freely in general.Hence, results in net positive electrostatic charges on semiconductor and negative electrostatic charges on polymer.Through a continuous friction, directional interfacial electric field finally forms at contact interface.
The measurement of device basic output properties about V oc and short-circuit current density (J sc ) in a vertical contact mode using a linear motor with programmable motion are shown in Figure 4.A source measure unit (SMU)-Keithley completes the acquisition of characteristic curves.To ensure measurement accuracy and reduce electrical drift, linear motor, and SMU-Keithley are grounded.Figure 4a is the V oc of ITO/c-TiO 2 /m-TiO 2 /CABB -PTFE/Al based TENG at a motion frequency of 0.25 Hz, where distinct output signals are ascribed to a power management circuit as Figure 5b illustrates.Direct output voltage without rectifier is measured through connecting the moving device to SMU-Keithley and is represented as V oc 1, while corresponding rectifier output is considered as V oc 3. Noteworthily, the input port of rectifier bridge is equivalent to an infinite impedance, where signals are denoted as V oc 2. Above tests are carried out on spin-coated and sprayed devices separately under same temperature and humidity, which V oc is 51 V and 105 V correspondingly, alleging a phenomenon that sprayed CABB TENG possesses higher triboelectric performance than spin-coated one.Additionally, V oc 3 usually manifests an upward trend than V oc 1. Figure 4b records direct output J sc 1 and rectifier output J sc 2 at similar condition as V oc .Conspicuously, J sc 1 exhibits the characteristics of alternating current (AC), and J sc 2 is rectified as the direct current (DC).Similar to V oc changes in fabrication process, J sc of sprayed film at 2.45 mA m −2 has a large increase than spincoated film at 0.9 mA m −2 , which is almost 2.7 times as much, meaning that output power capability could be increased accordingly.Motor mechanical frequency impacts on output characteristics are also discussed in Figure 4c,d that V oc and J sc boost accordingly as the frequency motion increases.When mechanical frequency increases from 0.125-10 Hz, V oc and J sc of spin-coated film separately raises from 51 V and 0.40 mA m −2 to 60 V and 2.88 mA m −2 .As the frequency reaches 2.5 Hz, the growth rate of V oc and J sc tend to be stable as shown in Figure S6a (Support-ing Information).Similarly, V oc and J sc of sprayed film surges from 105 V and 0.87 mA m −2 to 191 V and 8.72 mA m −2 as the same frequency pattern, where V oc and J sc demonstrate apparent advantage under 5 Hz motion.Detailed variation tendency of the sprayed film is also presented in Figure S7a (Supporting Information).However, with the frequency continues to rise to 10 Hz, V oc and J sc decline for the restricted charge transfer considering the transient contact. [62]When two surfaces rapidly contact and separate, an insufficient electrification effect occurs with less charges and lower voltages so that V oc and J sc decrease.The effects of contact area on output characteristics are also investigated in Figure 4e,f.As the area improves, the V oc and short-circuit current (I sc ) of spin-coated and sprayed films grow correspondingly.V oc of spin-coated and sprayed changes from 41 and 92 V to 103 and 155 V, and the I sc of both grow from 0.1 and 0.3 uA to 1.15 and 2.60 uA respectively, and the growth state are presented in Figures S6b and S7b (Supporting Information) as well.The insets of Figure 4e,f showed that as contact area increased, the ratio of sprayed to spin-coated film on V oc and J sc decreased.Although, the contact area was multiplied, the V oc and J sc changes unmultiplied obviously as Figure 4f, Figures S6b and S7b (Supporting Information) describe, whose appearance may be due to the incomplete polarization.Large-scaled CABB sprayed TENG with the area of 50 mm × 50 mm × 1.1 mm was fabricated as presented din Figure S10 (Supporting Information).The output voltage and output current could respectively achieve at 172 V and 3.16 uA at 0.25 Hz, and promising to the total output power.In addition, analogous experiments on V oc and J sc as described in Figure 4a,b were performed as shown in Figure 4g,h, except for the device revising through a replacement of PTFE with various polymers.Commonly used polymers like PVC, PVDF, PI, Nylon, FEP, and PET are constructed into new vertical contact mode TENG to evaluate the charging polarity of CABB.Like the polarity as PTFE possessed, positive V oc appears at the separation of PVC, PVDF, and PI-based TENG, where positive J sc occurs upon pressing and negative J sc upon releasing, signifying that CABB is positively charged and is a classical positive triboelectric material compared with above films.On the contrary, the TENG based on the polymers such as Nylon, FEP, and PET present negative effects like inverse V oc and J sc state compared with PTFE, etc., indicating that CABB could be negatively charged when in contact with these materials.Hence CABB polarity is between PI and FEP in these selected polymers.Furthermore, the analysis showed that output signals like V oc and J sc decrease along with the debasement of polarity difference between CABB and polymers.Concurrently, the ultimate trend of spin-coated and sprayed CABB TENG assembled with same polymer is identical as PTFE, suggesting that the characteristics of sprayed films' output are better than spin-coated one where surface properties like surface potential and roughness affect  r [63] and W f . [64]ong-term ceaseless test in all inorganic lead-free double perovskite CABB TENG output characteristics is presented in Figure 5a.After >900 s of continuous experiment, both spin-coated and sprayed CABB TENG with a mechanical frequency of 0.25 Hz demonstrate superior stability without any voltage attenuation.To further evaluate the output properties of CABB TENG fabricated through spin-coating and spraying method, the charging curves with different mechanical frequencies or capacitances and output power densities at various external load resistances were gained as shown in Figure 5. Figure 5b explicitly simplifies the equivalent circuit of full-bridge rectifier used above for power management that can convert AC signals generated from TENG to DC, profitably for energy utilization.Figure 5c,d,f,g,i substantiate the charging voltage influence factors, in terms of mechanical frequencies and capacitances.Figure 5c,f manifests the relationship between mechanical frequencies and the charging features.Regardless of the preparation process, the output response exhibits the same results that mechanical frequencies are positive to the charging voltage.The mechanical frequency at 10 Hz can  5i describes the connection between output characteristics and fabrication technique difference under the same testing condition.An apparent conclusion could be obtained that the CABB TENG fabricated through spraying method holds a stronger charge collection capability than that obtained by spin-coating, which agrees with previous discussion.Load voltage, load current density, and power density with various resistances are as portrayed in Figure 5e,h.As the resistance increased from 10 to 2 GΩ, load voltage increased gradually while load current density reduced.In light of the maximum power transfer theory, [24,65] the highest output power density can be acquired when external resistance matches the internal.The CABB TENG can fulfill a maximum power density at 0.051 W m −2 with an external load of 200 MΩ through spincoating method and 0.76 W m −2 with an external load of 300 MΩ through spraying method.Figure 5j displays the physical effect that TENG device with the power management circuit can light up at least 36 commercial yellow LEDs or 53 commercial yellow LEDs respectively under spin-coating and spraying method.This only requires ten seconds to charge 200 V for using 100 nF capac-itor as Figure S11 (Supporting Information) depicts.Some property comparisons are listed in Table 1, presenting different TENG structures and their output features.

Conclusion
In summary, vertical contact-separation TENGs comprised of all-inorganic lead-free CABB double perovskite and PTFE fabricated through spin-coating and spraying method are systematically studied for triboelectric behaviors, charge mechanism, and triboelectric charge polarities.CABB is certified as a classical positive triboelectric material simultaneously compared with PTFE, which polarity is located in PI and FEP as well.By various preparation technologies, sprayed film, with excellent output characteristics, are often ascribed to larger relative dielectric constant and work function difference.Besides, testing at 0.25 Hz mechanical frequency, sprayed CABB TENG with definitely robust stability in ambient atmosphere possesses the open circuit voltage (V oc ) at 105 V and short current density (J sc ) at 2.45 mA m −2 , higher than spin-coated one with V oc at 51 V and J sc at 0.9 mA m −2 .Mechanical frequency and effective contact area also have positive effects on output properties.After being equipped with power management circuit, smaller capacitance and larger mechanical frequency contribute to swifter charging speed and storage of the same electricity, and sprayed films presents stronger charge collection capability than spin-coated one as expected.Furthermore, sprayed CABB TENG fulfil a higher maximum power density at 0.76 W m −2 and could light up at least 53 commercial yellow LEDs in just 10 s using 100 nF capacitor while spin-coated one at 0.051 W m −2 when adjusted at 10 Hz.This work proposes

Figure 3 .
Figure 3. Whole "press-release" cycle of the TENG illustrated by motion displacement d: a) fully contacted, b) start releasing, c) fully released, and d) start pressing.e,f) The potential distribution analysis simulated by COMSOL Multiphysics software.The distance between ITO/c-TiO 2 /m-TiO 2 /CABB layer and PTFE layer are e) d = 0.5 um, and f) d = 4 mm.g) The ups spectra of ITO/c-TiO 2 /m-TiO 2 /CABB spin-coated and sprayed film.Where g 0 ) The ups spectra.g 1 ) The Wf spectra.g 2 ) The VB energy spectra.h) Detailed band energy structure of TENG.i) Bending energy structure of the heterojunction between TiO 2 and spin-coated or sprayed CABB film.j) The band structure of interfacial charge distribution under contact and separation, where contact with PTFE.

Figure 4 .
Figure 4. a) The open circuit voltage (V oc ) and b) The short current density (J sc ) of ITO/c-TiO 2 /m-TiO 2 /CABB -PTFE/Al TENG where CABB film is fabricated through spin-coating and spraying method.The relationship between c) V oc , d) J sc, and frequency.The relationship between e) V oc , f) J sc, and contact area.g) The V oc and h) The J sc of CABB-based TENG with various triboelectric films.CABB films were fabricated through spin-coating and spraying method.

Figure 5 .
Figure 5. a) Stability test of ITO/c-TiO 2 /m-TiO 2 /CABB -PTFE/Al TENG over 900s, where CABB film is fabricated through spin-coating and spraying method respectively.b) Power management circuit for rectifying alternating current (AC) output signals to direct current (DC).c,f) Charging curves of ITO/c-TiO 2 /m-TiO 2 /CABB -PTFE/Al TENG at various mechanical frequencies but same capacitance at 3.3 uF.d,g) Charging curves of ITO/c-TiO 2 /m-TiO 2 /CABB -PTFE/Al TENG at various capacitances but same mechanical frequency at 10 Hz. e,h) Output properties of ITO/c-TiO 2 /m-TiO 2 /CABB -PTFE/Al TENG on the voltage, current density, and power density at various external load resistances.CABB films were fabricated through c-e) spincoating and f-h) spraying method.i) A comparison of the ITO/c-TiO 2 /m-TiO 2 /CABB (fabricated through spin-coating and spraying method) -PTFE/Al TENG charging curves under the same test condition.j) The physical display effect of spin-coated and sprayed CABB TENG.j 1 ) 36 commercial yellow LEDs are lighted up by spin-coated CABB TENG.j 2 ) 53 commercial yellow LEDs are lighted up by sprayed CABB TENG.

Table 1 .
Output performance comparison of various perovskite-like materials based TENGs.