Alkoxysilane‐Treated SnO2 Interlayer for Energy Band Alignment of SnO2 Electron Injection Layer in Inverted Perovskite Light‐Emitting Diodes

Efficient inverted perovskite light‐emitting diodes (PeLEDs) are demonstrated by the introduction of tetraethyl orthosilicate (TEOS)‐incorporated tin oxide (SnO2) interlayer between the SnO2 electron injection layer and the perovskite emission layer. The TEOS incorporation into the SnO2 solution spontaneously converts it to a SiO2–SnO2 composite colloidal solution with a wide band gap, thermal stability, transparency, and chemical stability toward perovskite. The TEOS‐incorporated SnO2 interlayer effectively restricts the charge transfer from perovskite into SnO2 and promotes electron injection from SnO2 into perovskite due to the shift toward favorable energy band alignment. In addition, the TEOS‐treated interlayer balances the electron injection rate and the hole injection rate, thereby facilitating radiative recombination of the charge carriers injected into perovskite. As a result, the inverted PeLEDs exhibit significantly improved performance of 33 996 cd m−2 luminance, 9.99% of external quantum efficiency, and 44.83 cd A−1 of current efficiency.


Introduction
][9][10] Recognizing the growing demand for high-performance displays, our research underscores the significance of adopting the inverted structure.The inverted structure demonstrates greater compatibility than the normal structure in active matrix displays with n-type thin film transistors (TFT) backplanes, such as amorphous silicon or metal-oxidebased TFTs.[13] The inverted structure PeLEDs with high brightness, high efficiency, low turn-on voltage, and robust operational stability serve as crucial criteria for the development of active matrix-driven displays compatible with present TFT technology.
Inorganic metal oxide materials such as zinc oxide (ZnO), titanium oxide (TiO 2 ), and tin oxide (SnO 2 ) are widely employed as an electron transport layer (ETL) or as an electron injection layer (EIL) in various optoelectronic devices.[16] Among them, ZnO has been commonly used as an EIL for inverted green PeLEDs, as shown in Table S1 (Supporting Information), summarizing the recent advances in inverted green PeLEDs.However, the ZnO does not have good chemical stability toward the perovskite EML as it has been reported that the interfacial reaction between the ZnO and the perovskite layer leads to decomposition, consequently limiting its application to reliable PeLEDs. [17,18]o avoid such potential device degradation pathways, it is necessary to select stable and inert EILs for designing efficient inverted PeLEDs.As an alternative, chemically stable TiO 2 EIL has been attempted in PeLEDs, achieving 2.38% of maximum external quantum efficiency (EQE max ). [19]Meanwhile, SnO 2 EILs have also been widely implemented in optoelectronic devices owing to their superb chemical and thermal stability, high electron mobility, low-temperature solution-processability, and excellent optical transparency in the visible region, which can minimize the optical outcoupling loss derived from the EIL. [20]Furthermore, their deep valance energy band level and the wide bandgap structure impart excellent hole-blocking properties that are necessary for efficient EILs.Wang et al. fabricated SnO 2 -based near infrared PeLEDs with improved thermal and chemical stability compared to the ZnO-based PeLEDs. [21]Chen et al. applied additional SnO 2 EIL along with the conventional ZnMgO EIL in inverted quantum dot light-emitting diodes to enhance the charge injection and light coupling efficiency. [22]Despite these advantages, the conduction band minimum (CBM) of the SnO 2 lies at the deeper energy level compared to that of the perovskite layer. [23]Such a misaligned energy level is undesirable for preparing efficient PeLEDs because the large band offset between the SnO 2 and the perovskite emission layer induces electron transfer from perovskite to SnO 2 , causing significant photoluminescence (PL) quenching. [24,25]o overcome the undesired charge quenching issues while preserving the advantages of SnO 2 EIL, we introduced an alkoxysilane-treated SnO 2 interlayer in between SnO 2 EIL and perovskite EML for adjusting the band energy level alignment.[28] Recently, Matsushima et al. fabricated a siloxane network to form an insoluble poly(N-vinyl carbazole) (PVCz) hole transporting layer by incorporating tetraethyl orthosilicate (TEOS) to PVCz and demonstrated 15.4% of EQE max from a normal PeLEDs owing to the suppressed quenching of excited charges. [28]ere in this study, we modulate the band energy level of the SnO 2 -based EIL by controlling the TEOS concentration of the alkoxysilane-treated SnO 2 interlayer.The incorporated TEOS in SnO 2 colloidal solution converts into silicon oxide (siloxane) by the sol-gel reaction.The introduction of the alkoxysilane-treated SnO 2 interlayer improves energy band alignment favorable for charge injection and successfully suppresses PL quenching.Accordingly, we demonstrate up to ≈30-fold enhanced EQE max from the inverted PeLEDs with SnO 2 EIL by introducing TEOS-treated SnO 2 interlayer.

Results and Discussion
To confirm the change in energy band structures of EIL by the introduction of alkoxysilane-treated SnO 2 interlayers, we measured the optical and electrical properties of SnO 2 and TEOStreated SnO 2 interlayers with different volume percentages of TEOS, as shown in Figure 1.The bandgap (E g ) of each film was obtained from the Tauc plots with the UV-vis absorption spectra as shown in Figure 1a, and it was calculated from the following Equation (1): where  is the absorption value, h is the photon energy, and A is a constant.
It clearly shows that the E g of the SnO 2 and TEOS-treated SnO 2 interlayers gradually widen as the concentration of TEOS increases.The calculated E g of each film was 4.0, 4.37, 4.50, and 4.53 eV for SnO 2 films with 0 (control), 1, 5, and 10 vol.%TEOS incorporation, respectively.The Fermi energy level (E F ), the valence band maximum (E VBM ), and the conduction band minimum (E CBM ) were calculated from Equations (1-3): [29] E F = h − E cut−off (2) where h is the energy of He irradiation (21.22   S2 (Supporting Information).We confirmed that the TEOS-treatment increased the WF and CBM of interlayers due to the insulating characteristics of siloxane with wide E g .From the measured parameters, the corresponding schematic energy band diagram is illustrated in Figure 1c.
Through the TEOS-treatment, the band offset between the interlayer and the perovskite EML was gradually reduced, and it could be expected that the electron injection from ITO to perovskite EML through SnO 2 /TEOS-treated SnO 2 interlayer EIL is facilitated due to the altered band energy level alignment.
The direct current conductivity ( 0 ) of the SnO 2 EIL and TEOS-treated SnO 2 interlayers were determined based on the slope of the current-voltage (I-V) measurements for ITO/SnO 2 with control, 1, 5, and 10 vol.%TEOS/Au stacks, as shown in Figure 1d. [30]The thickness of each EIL for conductivity calculation is obtained from the scanning electron microscopy (SEM) cross-sectional images, as shown in Figure S1 (Supporting Information).As the concentration of TEOS increased, the thickness of the EIL tended to increase slightly.The overall thickness of the EIL was estimated to be ≈40, ≈41, ≈43, and ≈45 nm, corresponding to the concentrations of control, 1, 5, and 10 vol.%TEOS, respectively.The conductivity of pristine SnO 2 was 3.78 × 10 −6 S cm −1 , and the SnO 2 interlayer treated with 1, 5, and 10 vol.%TEOS had a gradual decrease in conductivity to 2.28 × 10 −6 , 1.34 × 10 −6 , 7.18 × 10 −7 S cm −1 , respectively.The SnO 2 is a good electron-accepting material, and consequently, the electrons in the perovskite are easily transferred into the SnO 2 layer, thus causing significant PL quenching of the excited state. [31,32][37] Thus, the TEOS-treated SnO 2 interlayer can contribute to modulating the electron injection rate and the resulting electron and hole injection balance, thereby enhancing the efficiency of PeLEDs.
We investigated the morphological properties of SnO 2 with different concentrations of TEOS.We investigated the morphological properties of SnO 2 with different concentrations of TEOS.As mentioned in the experimental section, the SnO 2 sol is syn-thesized from SnCl•2H 2 O, and consequently, the SnO 2 sol contains HCl acid.[40][41] This implies that the formed silicon oxide would form a SnO 2 -SiO 2 composite film rather than the coreshell structure of SnO 2 -silicon oxide, as shown in the transmission electron microscopy (TEM) images (Figure S2a-d, Supporting Information).
Figure S3 (Supporting Information) displays the morphological properties of the EIL using SEM surface images of the corresponding control, 1, 5, and 10 vol.%TEOS SnO 2 interlayer films deposited on glass substrates (Figure S3a-d, Supporting Information).Figure S3e-h (Supporting Information) represents the surface images of the perovskite layer on each respective EILs.All the EIL and the perovskite layer overlayers demonstrate uniform and pinhole-free films with complete coverage.These images indicate that the concentration of TEOS in EIL does not affect the perovskite film compatibility.
The X-ray photoelectron spectroscopy (XPS) characterizations are conducted to elucidate the differences in chemical properties between the pristine SnO 2 and TEOS-treated SnO 2 film condition.The full XPS spectrum of the survey scan, given in Figure S4 (Supporting Information), reveals peaks corresponding to pristine SnO 2 and the presence of Si attributed to TEOS treatment.With the addition of TEOS, the Si 2p peak emerged at 102.5 eV, indicating the presence of silicon oxide, as shown in Figure 2a.As shown in Figure 2b, the appearance of new peaks corresponding to silicon oxide in O 1s and Si 2p confirms the presence of silicon oxide in SnO 2 film.The O 1s maximum peak of pristine SnO 2 was at 530.2 eV, while the peak for TEOS condition was 530.8 and 532.4 eV caused by attributed to the Si─O bond, implying that a new silicon oxide bond was formed in the thin film.The binding energies of 495.0 and 486.6 eV correspond to the Sn 3d 3/2 and Sn 3d 5/2 peaks of pristine SnO 2 , respectively, as shown in Figure 2c.
Then, we compared the impacts of TEOS on perovskite films.When employing TEOS treatment, the perovskite film showed improved optoelectronic properties.Figure 3a is the UV-vis absorption spectra of the perovskite films and shows that all samples, irrespective of the TEOS concentration, have similar absorbance and on-set absorption edges at ≈540 nm in wavelength, which is a characteristic of perovskite film.This confirms that the introduction of TEOS-treated SnO 2 does not affect the bandgap and quality of the perovskite film.
The PL spectra were further analyzed in Figure 3b.While PL spectral shapes of the perovskite films remained the same, the PL intensities were greatly enlarged when introducing the TEOStreated SnO 2 interlayer.As a result, all samples have the same maximum PL peak position, as shown in a normalized static PL in Figure S5 (Supporting Information), indicating that the addition of TEOS does not affect the optical properties or crystallinity of the perovskite film.The time-resolved PL (TRPL) spectra in Figure 3c were measured to elucidate on the charge carrier recombination dynamics.We observed that TEOS-treated SnO 2 interlayers increased the PL lifetime of the perovskite films.The TRPL decay curves were fitted by the biexponential function with the following Equation ( 4): [42]  avg = ( where  1,  2, and  avg represent fast, slow, and average decay times, respectively, and A 1 and A 2 are the fractions corresponding to each component.All fitted parameters can be found in Table S3 (Supporting Information).The average PL lifetime for the perovskite film on pristine SnO 2 is calculated to be 16.73 ns, whereas the perovskite film on the SnO 2 treated with TEOS at 1, 5, and 10 vol.% concentrations exhibit an average PL lifetime of 26.55, 35.29, and 35.67 ns, respectively.From the static PL and TRPL results, we could conclude that greater TEOS incorporation at SnO 2 interlayers reduce the PL quenching of the excited states due to the more suppressed charge transfer. [28,43]However, no signifi-cant change in PL intensities and average lifetime was observed between 5 and 10 vol.%TEOS.This implies that the addition of the TEOS with an appropriate concentration improves the emissive properties of the perovskite film, which is advantageous for PeLEDs.
We further studied the current density-voltage (J-V) curves of electron-only devices (EODs) and hole-only devices (HODs) to compare the charge carrier mobility of the device with varying TEOS ratios.Space-charge-limited current (SCLC) measurement has been demonstrated as a useful method for evaluating the electrical characterization of PeLEDs in previous  studies. [44]EODs and HODs were fabricated with the structure of glass/ITO/SnO 2 /SnO 2 with control, 1, 5, and 10 vol.%TEOS/perovskite/1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBI)/Al and glass/ITO/PEDOT:PSS/perovskite/PTAA/Au, respectively.The electron mobility and the hole mobility were determined using the Mott-Gurney Law Equation ( 5): [45]  = where J D , L, ℇ, ℇ 0 , and V are the current density, the thickness of the perovskite layer, the relative dielectric constant, [46] vacuum permittivity, and the applied voltage in the SCLC region, respectively. [47]Figure 3d and Table S4 (Supporting Information) demonstrate that the control device exhibits imbalanced charge injection, where electron injection from the SnO 2 is faster than hole injection.This indicates that electrons could accumulate at the interface between the perovskite and HIL, thus causing electron leakage through HIL.The hole mobility measured 1.14 × 10 −4 , whereas the electron mobility decreased gradually from 1.05 × 10 −3 for the control group to 2.15 × 10 −4 , 6.42 × 10 −5 , and 1.98 × 10 −6 cm 2 (Vs) −1 under 1, 5, and 10 vol.%TEOS conditions, respectively.Notably, at TEOS concentrations of 1 and 5 vol.%, the electron mobility is closely approximated to hole mobility, suggesting a more balanced injection of charge carrier.At 10 vol.%TEOS concentrations, however, the electron injection was not efficient, exhibiting a significant disparity from the hole injection rate.Excessive and non-uniform carrier distribution in PeLEDs has been reported to induce strong non-radiative Auger recombination.Such process results in significant PL quenching and diminished de-vice efficiency. [25]Our findings emphasize the importance of optimizing TEOS concentration for achieving a balanced charge carrier in the PeLEDs.
To demonstrate the significance of TEOS-treated SnO 2 interlayers for device performance, we fabricated inverted PeLEDs.The device architecture of PeLEDs is composed of indium tin oxide (ITO)/SnO 2 /SnO 2 with different concentrations of TEOS/perovskite/PTAA/phosphomolybdic acid hydrate (PMAH)/Au.Figure 4a-d is current density-voltage-luminance (J-V-L) curves, EQE curves, current efficiency (CE), and normalized electroluminescence (EL) spectra curves of the device with control, 1, 5, and 10 vol.%TEOS-treatment samples.Notably, the device performance was greatly enhanced with the introduction of TEOS.
The EQE max and maximum luminance (L max ) of PeLEDs from control devices using pristine SnO 2 are only 0.34% and 5,495 cd m −2 , respectively.The TEOS-treatment improved the EQE max to 5.36%, 9.99%, and 1.27% for concentrations of 1, 5, and 10 vol.%, respectively.Thus, the CE max of the device was 1.64, 24.05, 44.83, and 5.19 cd A −1 for control, 1, 5, and 10 vol.%TEOS treatment, respectively.Similarly, L max was 26,287 cd m −2 for 1 vol.%TEOS, 33,996 cd m −2 for 5 vol.%TEOS, and 6,002 cd m −2 for 10 vol.%TEOS treatment, as shown along the left axis in Figure 4a and as summarized in Table 1.Normalized EL spectra of the samples in Figure 4d indicate that all samples have the same EL peak position and emission spectra width.
As the concentration of TEOS-treatment increases, the device performances were gradually improved, reaching the maximum values at 5 vol.%TEOS-treatment device.The device exhibited balanced charge injection into the perovskite EML, leading to higher luminance.Due to the gradual decrease of the electron injection energy barrier between EIL and perovskite, the turnon voltage (V on ) was lowered, accordingly.While the device with 10 vol.%TEOS-treated interlayer showed greatly suppressed leakage current density, the corresponding device exhibited the highest V on due to the insulating properties of excess silicon oxide in the interlayer.Overall, the balanced charge injection and the reduced leakage current by the introduced 5 vol.%TEOS-treated interlayer resulted in the highest EQE max and CE max values, as shown in Figure 4b,c.Although the 10 vol.%TEOS-treatment sample exhibited better optical properties (PL) than the 5 vol.%TEOS-treatment sample, the device performance showed poorer results.Consequently, we conducted additional studies on the TEOS 10 vol.% concentration.The high concentration of siloxane contained in EIL may have excessively interfered with charge injection due to the poor performance in the above EOD and device experiments.Therefore, we further diluted 10 vol.%TEOS-treated solution and checked their device performance.Dilutions were carried out at volume ratios of 1:0.5, 1:1, 1:5, and 1:10 for TEOS 10% solution by adding the corresponding amount of IPA solvent, and the performance of each device was shown in Figure S6 (Supporting Information).
It can be observed that a lower dilution ratio results in a delayed V on for luminescence.Similar to the original TEOS 10 vol.% treatment, its 1:1 and 1:0.5 dilution conditions initiated luminescence above 2.75 V.This indicates that the concentration of siloxane remains high, causing non-uniform charge injection, and further dilution is necessary for a thinner layer.Among these, the 1:5 dilution condition exhibited the highest efficiency and performance, with a significantly earlier V on of 2.25 V.However, under 1:10 dilution conditions, performance deteriorated due to insufficient film coverage resulting from the reduced concentration.It was evident that the turn on was pushed to 2.5 V due to the weakened luminescence intensity.Nevertheless, they still performed better than control SnO 2 , confirming the effect of TEOS treatment.Therefore, we found that the preceding 5 vol.%TEOS treatment was the most optimal concentration in terms of mobility and charge injection with HIL Finally, we compared the operational stability of the control and TEOS 5 vol.% device, as shown in Figure S7 (Supporting Information).The significantly enhanced operational stability of the 5 vol.%TEOS-treated device compared to the control device is attributed to the reduced leakage current and the enhanced lu-minescence due to the insulating property of silicon oxide, the proper energy band alignment of EIL, the reduced charge transfer from perovskite into SnO 2 , and the balanced electron and hole injection rate.

Conclusion
In summary, we have demonstrated efficient SnO 2 -based PeLEDs and reported on a facile method for preparing effective EIL by introducing TEOS.When employing 5 vol.%TEOS treatment on SnO 2 film for EILs, the CBM increased from 4.38 to 3.62 eV, and work function increased from 4.51 to 4.20 eV compared to the control samples.Accordingly, the reduced energy band offset between the EIL and perovskite layer enhanced charge injection properties.In addition, benefiting from the insulating properties of silicon oxide, electron mobility was able to reach the optimal point in balance between EIL and HIL.As a result, the best-performing devices exhibit CE max of 44.83 cd A −1 , EQE max of 9.99%, and L max of 33 996 cd m −2 .Our research indicates that incorporating TEOS-treated SnO 2 for the electron injection layer presents a promising approach for the development of high-performance inverted PeLEDs.

Preparation of Electron Injection Layer (EIL) Solution Incorporating TEOS:
The SnO 2 nanoparticles (NPs) were synthesized according to a previously reported method. [14]In short, 0.451 g of SnCl 2 •2H 2 O was dissolved into 20 mL of IPA and deionized H 2 O (95:5 v/v) mixture to obtain 0.1 m solution.The resulting solution was refluxed at 90 °C for 7 h.After the reaction was complete, a clear yellow solution was obtained.This solution was then cooled down to room temperature and filtered with 0.45 μm poly(tetrafluoroethylene) (PTFE) filter.The solution was diluted with IPA in a 1:1 (v/v) ratio and used as EILs.Additionally, the SnO 2 with TEOS treatment precursor solutions were prepared by varying a certain ratio of TEOS.The volume percentage of TEOS in the solution was tested within the range of 0-10 vol.%.The amount of SnO 2 in each solution was kept constant, and the TEOS ratio was adjusted under the control condition, SnO 2 :IPA (1:1).The 1 vol.%TEOS-treated solution was composed of SnO 2 :IPA:TEOS in a volume ratio of 1:0.99:0.01, the 5 vol.% solution of 1:0.95:0.05,and the 10 vol.% solution of 1: 0.9:0.1.Also, for experiments at 10 vol.% concentration, additional test solutions were prepared by diluting the 10 vol.%TEOS-treated solution with IPA in volume ratios of 1:0.5, 1:1, 1:5, and 1:10, while keeping other experimental conditions constant.
Device Fabrication: The patterned indium tin oxide substrates (ITO, 2.5 cm x 2.5 cm, etched area = 1 cm x 2.5 cm) were sonicated in deionized water with 5% detergent (Micro-90, International Products), ethanol, and acetone for 30 min each sequentially, and then air blowing was used to dry the substrates.After that, the ITO substrates were exposed to Ar/O 2 plasma treatment to obtain a hydrophilic surface.For the electron injection layer, the SnO 2 was deposited by spin-coating 200 μL of SnO 2 NPs solution at 3000 rpm for 30 s and followed by annealing at 150 °C for 30 min.Then, the 200 μL of TEOS-treated SnO 2 solutions (0, 1, 5, and 10 vol.%) were deposited on the SnO 2 film at 5000 rpm for 30 s and were annealed at 150 °C for 30 min.Substrates were performed with UV-ozone cleaner for 15 min before the deposition of the perovskite layer.The perovskite precursor solution was prepared by mixing FABr, MABr, GABr, CsBr, and PbBr 2 in a (FA 0.7 MA 0.1 GA 0.2 ) 0.87 Cs 0.13 PbBr 3 stoichiometric ratio in DMSO, as previously reported method. [48]The precursor solution was stirred overnight at room temperature and filtered with a 0.45 μm poly(tetrafluoroethylene) (PTFE) filter before use.After filtration, 100 μL of the solution was dropped on the ITO/EIL substrate with two spin-coating steps at 1000 rpm and 6000 rpm for 5 and 90 s, respectively.Chlorobenzene was dripped onto the perovskite film during the second spin step.For the hole injecting material, PTAA powder was dissolved in toluene at 7 mg mL −1 without any dopants, and the prepared solution was spin-coated at 3000 rpm for 30 s on the perovskite layer without thermal annealing.On top of the HTL, PMAH dissolved in IPA with a concentration of 5 mg mL −1 was spin-coated at 3000 rpm for 30 s, followed by baking at 100 °C for 10 min.(PMAH, which was a heteropoly acid containing MoO 3 , has been commonly used as an effective HIL in perovskite optoelectronic devices.) [12,49,50]Finally, 60 nm of the Au counter electrode was deposited by a thermal evaporation system under an ultra-high vacuum.The size of the active area was fixed at 0.04 cm 2 .The fabrication was completed by encapsulating the device with a glass lid and organic sealant.
Characterization: The ultraviolet photoelectron spectroscopy (UPS) spectra were obtained by a UV source: He1 21.22 eV (UPS, Thermo Fisher Scientific Co., theta probe base system).The ultraviolet-visible (UV-vis) absorption spectra were measured by a UV-vis spectrometer (3600 Plus, Shimadzu).The current-voltage (I-V) curves for estimating the conductivity of electron injection layers were obtained by a potentiostat (IviumStat, Ivium Technology).The current density-voltage-luminance characteristics of PeLEDs were obtained with a spectroradiometer (CS-2000, Konica Minolta) and a source measurement unit (2611B, Keithley).The static photoluminescence (PL) was obtained by a fluorophotometer (RF-6000, Shimadzu).The time-resolved photoluminescence (TRPL) spectra were measured using a photon-counting spectrofluorometer (PC1, ISS) under the irradiation of a 373 nm picosecond laser.The transmission electron microscopy (TEM) images were obtained using a field emission transmission electron microscope (FE-TEM, JEM-2100F, JEOL).The scanning electron microscopy (SEM) images were taken using a field emission scanning electron microscope (FE-SEM, Quanta 250 FEG).The X-ray photoelectron spectroscopy (XPS, X-TOOL, ULVAC-PHI) spectra were measured using Al K as the X-ray source and a beam diameter of 100 μm × 100 μm.The operational lifetime of PeLEDs was measured using an OLED reliability test system (RTS-101, 2HNM) under applied current conditions.

Figure 1 .
Figure 1.Optoelectronic properties of SnO 2 (control) and TEOS-treated SnO 2 interlayers: a) Tauc plots of control and TEOS-treated SnO 2 interlayers, b) UPS spectra of control and TEOS-treated SnO 2 interlayers (left = cut-off region, right = valence band region), c) corresponding schematic energy band diagram of the inverted PeLEDs, and d) I-V characteristics of ITO/control or TEOS-treated SnO 2 interlayers/Au.

Figure 3 .
Figure 3.The optoelectronic properties of perovskite on SnO 2 (control) and on SnO 2 /TEOS-treated SnO 2 interlayers: a) UV-vis absorption spectra, b) static PL spectra, and c) TRPL decay curves and d) J-V curves of the electron-only devices and hole-only device.
eV) and E cut-off and E VB stands for the secondary electron cut-off energy and the electron binding energy, which were obtained by linear extrapolations from the ultraviolet photoelectron spectroscopy (UPS) data, as shown in Figure 1b.The measured work functions (WFs) are −4.51,−4.27, −4.20, and −4.20 eV for SnO 2 film with control, 1, 5, and 10 vol.%TEOS incorporation, respectively.The calculated E CBM were −4.38 eV for pristine SnO 2 , −3.78 eV for 1 vol.%TEOS, −3.62 eV for 5 vol.%TEOS, and −3.57eV for 10 vol.%TEOS-treated SnO 2 interlayer.All parameters were summarized in Table

Table 1 .
Device performance of PeLEDs with various TEOS-treatment.