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Rei Usami, Koshi Oi, Keisuke Yamada, Jiang Pu, Hao Ou, Takahiko Endo, [Yasumitsu Miyata](https://orcid.org/0000-0002-9733-5119), [Taishi Takenobu](https://orcid.org/0000-0001-7313-6396)

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[Stepwise Engineering of Van der Waals Heterostructures for High Current Density in Light Emitting Devices](https://mdr.nims.go.jp/datasets/70b1aa19-c824-4798-84b5-d8fb40153e87)

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Advanced Electronic Materials www.advelectronicmat.deRESEARCH ARTICLEStepwise Engineering of Van der Waals Heterostructures for High Current Density in Light Emitting Devices Rei Usami1 Koshi Oi1 Keisuke Yamada1 Jiang Pu2 Hao Ou1 Takahiko Endo3 Yasumitsu Miyata3 , 4 Taishi Takenobu1 1 Department of Applied Physics, Graduate School of Engineering, Nagoya University, Nagoya, Aichi, Japan 2 Department of Physics, Institute of Science Tokyo, Tokyo, Japan 3 Department of Physics, Tokyo Metropolitan University, Tokyo, Japan 4 Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Nagoya University, Tsukuba, Ibaraki, Japan Correspondence: Taishi Takenobu ( takenobu@nagoya-u.jp) Received: 11 December 2024 Revised: 19 April 2026 Accepted: 25 May 2026 Keywords: electric double layer doping | light emitting device | Van der Waals heterostructure ABSTRACT Van der Waals (vdW) heterostructures of transition metal dichalcogenides (TMDs) have been widely employed in optoelectronic applications, including photodetectors, photovoltaic cells, and light-emitting devices (LEDs). Among these, PN-junction-based heterostructures are critical for advanced LED and laser applications, where achieving high current density is essential. However, the development of PN-junction-type LEDs using vdW heterostructures has been significantly hindered by the lack of effective doping techniques, resulting in devices with limited current densities. In this study, we propose a novel strategy for high- density carrier doping and reduced device resistance in vdW heterostructures by combining stepwise engineering of vdW stacking with electric double-layer (EDL) carrier doping. The stepwise-engineered heterostructure, based on WS2 /WSe2 , takes advantage of this configuration to facilitate efficient charge transport and enhanced carrier injection, as both P-type and N-type materials are in direct contact with the electrolyte, enabling high-density doping in both materials. Through EDL doping, clear electroluminescence was observed at the interface, with a peak current density of 9.4 × 104 A/cm2 . This result marks a significant advancement over previous reports, demonstrating a promising pathway toward vdW heterostructure-based laser applications. 1T  i  a  b  f  [  d  c  c  v  f            To©Ah Introduction he integration of dissimilar materials into heterostructuress essential for a wide range of electronic and optoelectronicpplications [ 1, 2 ]. In particular, light-emitting devices (LEDs)ased on PN junctions in semiconductor heterostructures areundamental for advanced light sources and laser technologies 1–4 ]. Recently, the development of novel heterostructures usingangling-bond-free van der Waals (vdW) materials, which are notonstrained by lattice mismatch, has been realized with semi-onductor transition metal dichalcogenides (TMDs) [ 5–8 ]. ThesedW heterostructures have enabled the fabrication of variousunctional devices, including PN junctions [ 9, 10 ], photovoltaichis is an open access article under the terms of the Creative Commons Attribution Licenriginal work is properly cited. 2026 The Author(s). Advanced Electronic Materials published by Wiley-VCH GmbH dvanced Electronic Materials , 2026; 12:e00930 ttps://doi.org/10.1002/aelm.202400930cells [ 11 ], and photodetectors [ 12 ]. However, most reports onTMD-based LEDs involve tunneling structures with hexagonalboron nitride tunneling layers [ 13–15 ]. In contrast, there are sur-prisingly few studies on pure PN junction-based LEDs made fromTMD heterostructures, despite this being the standard devicestructure for cutting-edge light sources and laser applications [ 16–20 ]. One major challenge is the lack of effective doping methodsfor TMD semiconductors. Furthermore, although achieving highcurrent density is crucial for laser applications, reports on currentdensity in these devices remain scarce. To address this issue, we focused on electrolyte-based electricdouble-layer (EDL) doping, which has been shown to achievese, which permits use, distribution and reproduction in any medium, provided the 1 of 9http://www.advelectronicmat.dehttps://doi.org/10.1002/aelm.202400930https://orcid.org/0000-0001-7313-6396mailto:takenobu@nagoya-u.jphttp://creativecommons.org/licenses/by/4.0/https://doi.org/10.1002/aelm.202400930http://crossmark.crossref.org/dialog/?doi=10.1002%2Faelm.202400930&domain=pdf&date_stamp=2026-06-01e  T  i  a  f  A  r  (3  v  h  E  h  a  oT  t  c  N  c  W  t  d  l22FT  d  o  e  ao  t  t  c  T3  s  u  P  b  t  a  s  h  p  cT m  c  w  N  w  v  FIGURE 1 Proposed device structure and fabrication of vdW het- erostructure. Schematic representations of (a) the previous and (b) the proposed stepwise-engineered EDLEDs. (c) Optical micrograph of the fabricated vdW heterostructure, with P-type WSe2 on top and N-type WS2 on the bottom. The scale bar represents 100 µm. (d) PL spectra of WSe2 (top) and WS2 (bottom).                   2 2199160x, 2026, 16, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/aelm.202400930 by National Institute For, Wiley Online Library on [19/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatxtremely high doping densities exceeding 1014 /cm2 [ 20–25 ].his technique has enabled doping-induced phase transitionsn semiconductor TMDs, such as ambipolar carrier transportnd electric field-induced superconductivity—key phenomenaor forming PN junctions and achieving high current density.dditionally, PN junction-type LEDs have been successfully fab-icated using this doping method, with clear electroluminescenceEL) emissions observed in monolayer semiconductor TMDs [ 26–2 ], in-plane TMD heterostructures [ 33, 34 ], and out-of-planedW heterostructures [ 20 ]. These results strongly suggest thatigh current densities can be achieved through high-densityDL doping. However, directly applying EDL doping to vdWeterostructures presents challenges, as the emission positionnd area can shift with applied voltage, complicating the analysisf current densities [ 20 ]. o confront these challenges, we propose a novel device struc-ure based on stepwise engineering of vdW heterostructures,ombining EDL doping with a P-type WSe2 monolayer and an-type WS2 monolayer. We observed non-linear current-voltageharacteristics and fixed-position EL at the interface betweenSe2 and WS2 , confirming the formation of a PN junctionhrough heterostructure design. Notably, the estimated currentensity reached 9.4 × 104 A/cm2 , presenting a new pathway foraser applications based on vdW heterostructures.  Results and Discussion .1 Proposed Device Architecture and abrication wo-terminal LEDs based on EDL doping, known as electric-ouble-layer LEDs (EDLEDs), are unique devices that requirenly a luminescent material, a two-terminal electrode, and anlectrolyte [ 31–33 ]. As illustrated in Figure 1a , by simply applying voltage between the two electrodes, two types of EDL doping—ne for holes and the other for electrons—are self-assembled onhe semiconductor surface, leading to the formation of a PN junc-ion and EL emission. This concept was first proposed for organiconjugated polymers [ 35–37 ] and has recently been extended toMDs, including monolayers and in-plane heterostructures [ 31–4 ]. In this study, as shown in Figure 1b , we propose a devicetructure based on stepwise engineering, which incorporates anpper electrolyte and a lower staircase-shaped heterostructure of- and N-type semiconductors. The electrolyte directly contactsoth P- and N-type materials, which is essential for forminghe EDL layer on the semiconductors. Notably, in monolayernd in-plane heterostructure EDLEDs, the light-emitting zonehifts depending on the applied voltage [ 31–34, 38 ], whereas vdWeterostructures with vdW gaps are expected to provide fixed-osition light emission. This characteristic is advantageous forreating LEDs with optical resonators and future laser devices. o fabricate a heterostructured PN junction, we selected a WSe2onolayer as the P-type semiconductor due to its strong P-typeurrent in EDL transistors [ 38, 39 ]. Similarly, a WS2 monolayeras chosen as the N-type semiconductor, owing to its significant-type current in EDL transistors [ 38 ]. The target materialsere single-crystalline triangular monolayers grown via chemicalapor deposition (CVD) [ 34 ], where the edges of the CVD-grownof 9single crystals exhibit zigzag configurations [ 34, 40 ]. This featureenables precise control over the twist angle between the WSe2 and WS2 monolayers. As shown in Figure 1c , we aligned thezigzag edges of the single-crystal WSe2 and WS2 monolayers (twistangle = 0◦), with the electrodes also aligned parallel to the zigzagedges. This ensures that carrier transport occurs in the armchairdirection at the interface between WSe2 and WS2 , facilitatingefficient charge transfer across the junction. To confirm the monolayer status of the samples, we collectedphotoluminescence (PL) spectra using a 532 nm laser (JASCONRS-5100). The PL spectra shown in Figure 1d confirmed themonolayer nature of the materials [ 38 ]. Given that WSe2 istypically smaller than WS2 , we selected the larger WS2 monolayer,grown on a SiO2 /Si substrate, as the bottom layer. The smallerWSe2 monolayer was then transferred onto the WS2 layer. Finally,the ion-gel, composed of a triblock copolymer (poly(styrene-block-methyl methacrylate-block-styrene), PS-PMMA-PS; MPS= 4.3 kg/mol, MPMMA = 12.5 kg/mol, Mw = 21.1 kg/mol)and an ionic liquid, N , N -Diethyl- N -methyl- N -(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)imide ([DEME][TFSI]),Advanced Electronic Materials, 2026ive Commons LicenseFIGURE 2 Current-voltage characteristics and EL emission in vdW heterostructure of WS2 and WSe2 . (a) Optical micrograph of the fabricated vdW heterostructure device, where the electrode on N-type WS2 is the cathode, and the electrode on P-type WSe2 is the anode. Scale bar: 10 µm. (b) Current- voltage characteristics of the vdW heterostructure composed of WS2 and WSe2 . (c) Optical micrograph of the EL emission from the vdW heterostructure of WS2 and WSe2 . Scale bar: 10 µm. d  s  T  0  t2EA  w  a  a  E  d  t  c  w  t  W  a  i  t  C  P  a  a  e  a  WT  j  a  t  o                                A 2199160x, 2026, 16, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/aelm.202400930 by National Institute For, Wiley Online Library on [19/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatissolved in ethyl propionate [ 31–37 ], was spin-coated onto theurface of the stepwise heterostructure at 6000 rpm for 120 s.he weight ratio of the copolymer, ionic liquid, and solvent was.7:9.3:90. For details on the optimized conditions, please refer tohe Methods Section. .2 Current–Voltage Characteristics and lectroluminescence s shown in Figure 2a , the current ( I )—voltage ( V ) characteristicsere investigated with the electrode on the P-type WSe2 as thenode and the electrode on the N-type WS2 as the cathode, using semiconductor parameter analyzer (Agilent Technologies, Inc.5270) in a shielded probe station. All experiments were con-ucted in a glove box under a nitrogen atmosphere at roomemperature. As shown in Figure 2b , we observed non-linearurrent-voltage characteristics for both forward and reverse bias,ith clear rectification behavior. These results are consistent withhose observed in EDL transistors, where the P-type current of theSe2 monolayer and the N-type current of the WS2 monolayerre relatively larger than their opposite-charge counterparts,ndicating the formation of a PN junction. To further confirmhis, we observed the device under voltage application using aCD camera (SHODENSHA) and a spectrometer (Hamamatsuhotonics K.K., Lambda Vision SA-100C-HPCB/C). Once again,ll experiments were performed in a glove box under a nitrogentmosphere at room temperature. As shown in Figure 2c , clear ELmission was observed at the WSe2 /WS2 heterostructure interfacet 3.4 V, confirming the formation of the PN junction at theSe2 /WS2 interface. o gain a deeper understanding of the formation of the PNunction, we also investigated the transient current-voltage char-cteristics, as the dynamic response of ions is much slower thanhat of the hole and electron carriers. Based on previous reportsn EDLEDs using monolayer TMDs [ 31, 32 ], we analyzed thedvanced Electronic Materials, 2026I –V characteristics by dividing them into three distinct regimesand comparing their time-dependent currents, as shown in thelogarithmic plot of the applied voltage ( V ) versus the absolutecurrent (| I |) in Figure 3a . First, as shown in Figure 3b , in regime (I) of Figure 3a , weobserved a typical ion displacement current without a clearenhancement of the base current. This suggests the formationof EDL capacitors on the electrode surfaces. As illustrated inFigure 1a,b , applying an electric field redistributes anions andcations, forming EDLs on each electrode. These EDLs createa strong electric field and induce steeper band bending at themetal/TMD interfaces. Next, in regime (II), shown in Figure 3c , two distinct contri-butions were observed. Similar to regime (I), one contributionwas the ion displacement current, attributed to the formation ofEDLs. In addition, a nonlinear increase in the base current wasobserved, indicating time-dependent conductivity enhancementin WSe2 and/or WS2 due to EDL capacitor formation. Thissuggests that in regime (II), an EDL doping layer is forming on theTMD surfaces. The relatively small enhancement in base currentmay indicate that the EDL doping primarily occurs in one of theTMDs, either WSe2 or WS2 . Finally, as shown in Figure 3d , in regime (III) of Figure 3a , atransient increase in current was observed. This large increasein transient current indicates the gradual spread of a 2D chargesheet and the formation of EDL capacitors on the surfaces ofboth WSe2 and WS2 . This result is consistent with the observationof EL emission from the WSe2 /WS2 heterostructure interface at3.4 V, which corresponds to region (III). Notably, while theseresults qualitatively agree with those observed for EDLEDs usingmonolayer TMDs, the significant change between regimes (II)and (III) in Figure 3a is a unique feature of vdW heterostructuresand strongly suggests the influence of the vdW gap (Section S1 )[ 31, 32 ]. 3 of 9ive Commons LicenseFIGURE 3 Transient current-voltage characteristics in the vdW heterostructure of WS2 and WSe2 . (a) Logarithmic plot of the applied voltage ( V ) dependence of absolute current (| I |). Transient current responses of the fabricated vdW heterostructure device under the application of constant voltage: (b) 0 V ≤ V ≤ 0.3 V, (c) 1.6 V ≤ V ≤ 2.2 V, and (d) 2.4 V ≤ V ≤ 2.9 V. These three transient behaviors correspond to regimes I, II, and III as defined in Figure 3a. 2AA  W  r  a  i  p  t  t  f  i  h  tI  a  t  d  t h  T  o                       4 2199160x, 2026, 16, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/aelm.202400930 by National Institute For, Wiley Online Library on [19/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable .3 Fixed-Position Electroluminescence chieved Through Heterostructure Design s mentioned above, clear EL emission was observed from theSe2 /WS2 heterostructure interface at 3.4 V, corresponding toegime (III). As illustrated in Figure 1b , this fixed EL emissionligns with the stepwise-engineered EDLED design. To furthernvestigate, we examined the voltage dependence of the ELroperties. As shown in Figure 4a , the EL intensity detected byhe CCD camera increased with voltage from 2.9 to 3.4 V. Notably,he EL color and position remained almost constant, confirmingixed-position EL emission from the WSe2 /WS2 heterostructurenterface. It is important to note that in monolayer and in-planeeterostructure EDLEDs, the position of the light-emitting zoneypically shifts with applied voltage (Section S2 ) [ 31–34, 38 ]. n monolayer and in-plane heterostructure EDLEDs, applying voltage modifies not only the semiconductor region but alsohe EDL, leading to changes in the spatial distribution of carrierensity within the sample. This dynamic redistribution causeshe light-emitting zone to shift. In contrast, for WSe2 /WS2eterostructures, the vdW gap at the interface plays a critical role.he resistance of the vdW gap is significantly higher than thatf the semiconductor regions, which causes the potential dropof 9Creaand the spatial distribution of carrier density to be predominantlydetermined by the vdW gap. Additionally, charge accumulationwithin the semiconductor regions requires the applied voltageto exceed the threshold voltage specific to each material. Sincethe threshold voltages of WSe2 and WS2 differ, charge sheetsdo not extend across the vdW gap. This prevents significantcarrier redistribution across the interface and contributes to thefixed emission position. The combination of these effects—highvdW gap resistance and localized charge accumulation due todiffering threshold voltages—ensures that the emission positionremains pinned at the heterostructure interface, independent ofthe applied voltage. This behavior is particularly advantageous forapplications requiring stable and localized light emission, such asoptical resonators and laser devices. To clarify the luminescence mechanism, we further analyzedthe EL spectrum and compared it with the PL characteristics ofthe same sample. As shown in Figure 4b,c , the EL spectrum ismuch closer to the direct-gap emission of WS2 than to that ofWSe2 or to the interlayer transition expected for the WS2 /WSe2 heterostructure, strongly suggesting that the EL originates fromWS2 . This observation appears inconsistent with the simpleband alignment expected from theory. According to the reportedband offsets for the WS2 /WSe2 heterojunction [ 41 ], as shownAdvanced Electronic Materials, 2026tive Commons LicenseFIGURE 4 EL properties in the vdW heterostructure of WS2 and WSe2 . (a) Voltage dependence of the optical micrograph showing EL emission from the vdW heterostructure of WS2 and WSe2 . The scale bar represents 10 µm. (b) EL spectrum (red) of the vdW heterostructure EDLED compared with the PL spectrum (black) of the WS2 monolayer. (c) Voltage dependence of EL spectra. (d) Theoretical band profile of the WS2 /WSe2 heterojunction. (e) WSe2 PL peak mapping, (f) WS2 PL peak mapping. The black dotted lines indicate the edge of top WSe2 monolayer. i  t  t  WT  f  t  F  2  v  p  a  r  s  s  a  c  W  o  m  i  E                    A 2199160x, 2026, 16, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/aelm.202400930 by National Institute For, Wiley Online Library on [19/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicablen Figure 4d , the conduction-band offset is ΔEC = 0.32 eV andhe valence-band offset is ΔEV = 0.62 eV, which would suggesthat recombination should occur more readily in WSe2 than inS2 . o examine whether local variation of the bandgap could accountor the observed WS2 EL, we performed spatial mapping ofhe PL peak energies on the identical sample. As shown inigure 4e,f , the observed PL peak energies ranged from 1.90 to.05 eV for WS2 and from 1.61 to 1.64 eV for WSe2 . Although thesealues exhibit broader spatial variation than typically reported forristine monolayer WS2 and WSe2 , presumably due to local strainnd/or transfer-induced inhomogeneity, the observed variationemains much smaller than the several-hundred-meV energycale relevant to the interfacial injection asymmetry, as repre-ented by the theoretically expected band offsets ( ΔEC = 0.32 eVnd ΔEV = 0.62 eV). Therefore, local bandgap variation aloneannot account for the reversal from the theoretically expectedSe2 -side recombination to the experimentally observed WS2 -rigin EL. These results suggest that the dominant factor is noterely the intrinsic bandgap, but rather the effective carriernjection process across the heterointerface under high-densityDL doping. dvanced Electronic Materials, 2026A more plausible explanation is that the effective injection barrieris substantially modified by the strong local electric field formedacross the van der Waals gap during operation. Previous studieson MoS2 /WSe2 heterointerfaces have suggested that interfacialcharge transfer can modify the electronic structure beyondthe simple equilibrium band alignment expected from isolatedmonolayers [ 42 ]. In the present WS2 /WSe2 device, such interfacialmodulation may be further enhanced under high-density EDLdoping, because electrons accumulated on the WS2 side andholes accumulated on the WSe2 side near the heterointerfacecan generate a strong local electric field across the van derWaals gap. This local field may substantially alter the effectiveband profile and the relative injection barriers during operation,thereby making hole injection into WS2 more plausible thanwould be expected from the simple equilibrium band alignment. Another, more speculative, possibility is that hole injection fromWSe2 to WS2 is assisted by local metallization at the WSe2 edge,analogous to edge metallization reported in other TMD systemssuch as MoS2 and MoSe2 [ 43, 44 ]. To the best of our knowledge,however, there is currently no direct experimental evidence forsuch a mechanism in WSe2 , and we therefore regard this only asa tentative possibility. 5 of 9 Creative Commons LicenseF  d  b  f  p  d  g  t  p  i  p  hA  v  b  t  a  s  m  t  t  v  2SF  e  s  i  o  c  c  b  tT  r  d  h  i  b  a  t  d  dT  l  e  P  t  c  rT  c  h  (  FIGURE 5 Current density as a function of applied voltage in vdW heterostructure EDLEDs. The results demonstrate the characteristic I –V behavior of the device, highlighting the impact of the stepwise-engineered heterostructure.                                6 2199160x, 2026, 16, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/aelm.202400930 by National Institute For, Wiley Online Library on [19/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creaturther clarification of the dominant mechanism will requireirect probing of the local potential profile and effective injectionarrier near the heterointerface. In particular, Kelvin probeorce microscopy would be a powerful method to examine localotential redistribution and band bending, while temperature-ependent EL and transport measurements would help distin-uish between thermally activated injection and field-assisted orunneling-like processes. Although the detailed recombinationathway remains to be clarified, the present results clearlyndicate that the vdW heterointerface is responsible for the fixed-osition EL, which is a unique feature of the stepwise vdWeterostructure. s shown in Figure 4e , the PL peak energy exhibits clear spatialariation in the monolayer WS2 region. Therefore, a comparisonased on a single PL spectrum is not sufficient for discussinghe spectral relationship between PL and EL. To obtain a moreppropriate reference spectrum, we constructed the PL spectrumhown in Figure 4b by summing PL spectra extracted fromultiple points in the monolayer WS2 region as close as possibleo the EL emission site near the WS2 /WSe2 boundary. Based onhis analysis, we find that the peak energy of the EL spectrum is inery good agreement with that of the corresponding PL spectrum..4 Achieving High Current Density in tepwise-Engineered vdW Heterostructure EDLEDs inally, we estimated the current density in the stepwise-ngineered vdW heterostructure EDLED. In this device, thetepwise design facilitates hole injection from the top WSe2 layernto the bottom WS2 layer, where hole–electron recombinationccurs on the WS2 side of the heterostructure interface. Toalculate the current density, we defined the cross-section of theurrent path at the light-emitting zone as a rectangle formedy the WSe2 /WS2 interface length (127.5 µm) and the WS2 layerhickness (0.7 nm). he resulting current density–voltage relationship in the voltageange of 2.9 to 3.4 V is shown in Figure 5 . A maximum currentensity of 9.4 × 104 A/cm2 was achieved, which is significantlyigher than that of conventional laser diodes [ 45 ]. Additionally, asllustrated in Figure 3a , the device current increases dramaticallyy five orders of magnitude, from ∼ 10− 9 A at 1 V to ∼ 10− 4 At 3.5 V. This substantial amplification strongly indicates thathe stepwise-engineered structure and the formation of the EDLoping layer play crucial roles in achieving such high currentensity. he proposed stepwise-engineered heterostructure is particu-arly advantageous because it enables direct contact with thelectrolyte, forming efficient EDL doping layers for both the- and N-type semiconductors. This design minimizes resis-ance throughout the device, except at the PN interface. Theseharacteristics are pivotal for enhancing carrier injection andecombination efficiency. o benchmark the present device, we compared the reportedurrent densities of representative monolayer, few-layer, andeterostructure TMD light-emitting devices in the literatureTables S1 and S2 ). This comparison highlights that electrolyte-of 9gated devices generally reach much higher current densitiesthan devices based on other doping schemes, and that thepresent WS2 /WSe2 device is among the highest-current-densitybilayer/heterostructure devices reported to date. A summary ofthe additional device statistics, including an additional WSe2 /WS2 emitting device and the peak current-density distribution acrossstepwise heterostructure devices, is provided in Figures S3 and S4 .Although a quantitative evaluation of the EL efficiency is beyondthe scope of the present study because the optical setup wasnot calibrated for absolute photon collection, previous studieson monolayer EDL emitters have shown that the EL efficiencyis typically well below 1% [ 31, 32 ]. In this context, the observedincrease in EL intensity with current, together with the absenceof marked spectral broadening or degradation, suggests thatradiative recombination remains operative at the heterointerfaceand that nonradiative loss and severe Joule heating do not dom-inate within the present operating range, although quantitativeevaluation of the efficiency in the present heterostructure devicewill be an important subject for future work. TMDs have already been combined with optical resonators torealize optically pumped lasing-related devices [ 46 ], and veryrecently electrically driven TMD laser operation has also beenreported [ 47 ]. From this perspective, further development ofTMD-based laser devices will benefit from electrically drivenstructures that are relatively simple, compatible with optical-cavity integration, and capable of sustaining both fixed-positionemission and high current injection. The present stepwise-engineered heterostructure has these favorable features: a com-paratively simple device structure, electroluminescence localizedat a fixed heterointerface position, and high current density.These characteristics make the present architecture a promisingplatform for future integration with optical resonators and forexploring more advanced current-driven vdW heterostructureAdvanced Electronic Materials, 2026ive Commons Licensel  o  b  t  W3I  a  e  v  p  e  s  n  a  0  e  l  o  o  b  n  b  o44HT  m  d  s  s  1  w  h  m m  S  r  w  p  s  A a  o4T  s  a  t  c                                 A 2199160x, 2026, 16, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/aelm.202400930 by National Institute For, Wiley Online Library on [19/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creatight sources. More broadly, electrically driven high-injectionperation assisted by electrostatic carrier accumulation has alsoeen explored in other material systems [ 51, 52 ], suggestinghat the present strategy may be relevant beyond the specificS2 /WSe2 heterostructure studied here.  Conclusions n this study, we proposed a novel and innovative strategy tochieve high current density in vdW heterostructure-based light-mitting devices. This strategy leverages a stepwise-engineereddW stacking design combined with EDL carrier doping. Theroposed device structure is remarkably simple, requiring only anlectrolyte thin film deposited on the stepwise-engineered vdWtacking along with two electrodes. To demonstrate the effective-ess of this approach, we employed a WS2 /WSe2 heterostructure,chieving an exceptionally high current density of approximately.1 MA/cm2 . Notably, the stepwise-engineered heterostructurenabled stable EL emission localized at a fixed position under aateral bias. These findings underscore the significant potentialf this device architecture for integration with optical resonators,pening new avenues for the realization of laser applicationsased on vdW heterostructures. We believe that this approachot only provides a pathway to enhance device performanceut also contributes to the broader development of advancedptoelectronic technologies.  Experimental Section .1 Preparation of Van der Waals eterostructures he vdW stacks were fabricated using a polymer-assisted transferethod [ 48, 49 ]. As the polymer, we prepared Elvacite 2552Cissolved in anisole (weight ratio 1:1.5). Prior to sample collection,mall drop of polymer was picked and transferred onto glasslide using a toothpick. The slide glass was then annealed at80◦C in air for 1 h. The polymer was first put into contactith the WSe2 monolayer at 90◦C, and the transfer stage waseated to 160◦C to increase the contact area. Subsequently, theonolayer was picked up at 60◦C. The polymer with WSe2onolayer was brought into contact with the WS2 monolayer oni/SiO2 substrate at 170◦C, at which the polymer would melt. Byemoving the substrate from the glass slide, part of the polymeras left on the substrate, with the WSe2 monolayer. The residualolymer was then washed away by sequentially immersing theubstrate in chloroform (2 min) and isopropyl alcohol (2 min).fter fabricating the staircase-shaped heterostructure of WSe2nd WS2 , Au/Ni electrodes (40/2.5 nm) were thermally depositedn both materials through the shadow mask. .2 Optimization of Ion-Gel Films he ion-gel composition strongly influences the film thickness,urface morphology, ionic conductivity, and mechanical stability,ll of which affect the efficiency of EDL doping. Accordingo our previous optimization study [ 50 ], increasing the solventontent and/or the ionic-liquid content relative to the polymer,dvanced Electronic Materials, 2026as well as increasing the spin-coating speed, reduces the filmthickness, whereas decreasing the ionic-liquid content lowers theionic conductivity and makes the gel mechanically harder. Inthe present study, the composition and spin-coating conditionswere chosen so that the film remained sufficiently thin andflat for stable optical measurements, while maintaining ionicconductivity high enough for effective EDL doping. The presentratio was selected as a practical balance among these competingrequirements. Acknowledgements This work was financially supported by JSPS KAKENHI Grant Num-bers JP20H05867, JP20H05664, JP21H05232, JP21H05234, JP21H05236,JP22H00280, JP22H04957, JP22KJ1555, JP22K19059, and JP22H01899, aswell as by JST CREST Grant Numbers JPMJCR23A4 and JPMJCR23O3,Japan. 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Sawabe, T. Takenobu, S. Z. Bisri, T. Yamao, S. Hotta, and Y. Iwasa,High Current Densities in a Highly Photoluminescent Organic Single-rystal Light-Emitting Transistor,” Applied Physics Letters 97 (2010):43307, https://doi.org/10.1063/1.3466915 . upporting Information dditional supporting information can be found online in the Supportingnformation section. upporting File : aelm70445-sup-0001-SuppMat.docx. dvanced Electronic Materials, 2026 9 of 9ary on [19/10/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttps://doi.org/10.1002/adma.202509861https://doi.org/10.1038/s41467-018-03723-whttps://doi.org/10.1039/D3NA00371Jhttps://doi.org/10.1063/1.3466915 Stepwise Engineering of Van der Waals Heterostructures for High Current Density in Light Emitting Devices 1 | Introduction 2 | Results and Discussion 2.1 | Proposed Device Architecture and Fabrication 2.2 | Current-Voltage Characteristics and Electroluminescence 2.3 | Fixed-Position Electroluminescence Achieved Through Heterostructure Design 2.4 | Achieving High Current Density in Stepwise-Engineered vdW Heterostructure EDLEDs 3 | Conclusions 4 | Experimental Section 4.1 | Preparation of Van der Waals Heterostructures 4.2 | Optimization of Ion-Gel Films Acknowledgements Conflicts of Interest Data Availability Statement References Supporting Information