Cover Picture: n‐Channel,Ambipolar, and p‐Channel Organic Heterojunction Transistors Fabricated with Various Film Morphologies (Adv. Funct. Mater. 3/2007)

Simultaneous introduction of short‐range repulsive interactions between dissimilar colloidal particles and attractive interactions between like particles provides a general new route to fabricating self‐organizing bipolar devices. By identifying combinations of conductive device materials between which short‐range repulsive forces exist in the presence of an intervening liquid, electrochemical junctions can be self‐formed, as reported by Chiang and co‐workers on p. 379. The relationship between the performance characteristics of organic field‐effect transistors (OFETs) with 2,5‐bis(4‐biphenylyl)bithiophene/copper hexadecafluorophthalocyanine (BP2T/F₁₆CuPc) heterojunctions and the thickness of the BP2T bottom layer is investigated. Three operating modes (n‐channel, ambipolar, and p‐channel) are obtained by varying the thickness of the organic semiconductor layer. The changes in operating mode are attributable to the morphology of the film and the heterojunction effect, which also leads to an evolution of the field‐effect mobility with increasing film thickness. In BP2T/F₁₆CuPc heterojunctions the mobile charge carriers accumulate at both sides of the heterojunction interface, with an accumulation layer thickness of ca. 10 nm. High field‐effect mobility values can be achieved in continuous and flat films that exhibit the heterojunction effect.     

Heterojunction Ambipolar Organic Transistors Fabricated by a Two‐Step Vacuum‐Deposition Process

Ambipolar organic field‐effect transistors (OFETs) are produced, based on organic heterojunctions fabricated by a two‐step vacuum‐deposition process. Copper phthalocyanine (CuPc) deposited at a high temperature (250 °C) acts as the first (p‐type component) layer, and hexadecafluorophthalocyaninatocopper (F₁₆CuPc) deposited at room temperature (25 °C) acts as the second (n‐type component) layer. A heterojunction with an interpenetrating network is obtained as the active layer for the OFETs. These heterojunction devices display significant ambipolar charge transport with symmetric electron and hole mobilities of the order of 10^–4 cm² V^–1 s^–1 in air. Conductive channels are at the interface between the F₁₆CuPc and CuPc domains in the interpenetrating networks. Electrons are transported in the F₁₆CuPc regions, and holes in the CuPc regions. The molecular arrangement in the heterojunction is well ordered, resulting in a balance of the two carrier densities responsible for the ambipolar electrical characteristics. The thin‐film morphology of the organic heterojunction with its interpenetrating network structure can be controlled well by the vacuum‐deposition process. The structure of interpenetrating networks is similar to that of the bulk heterojunction used in organic photovoltaic cells, therefore, it may be helpful in understanding the process of charge collection in organic photovoltaic cells.     

High‐Performance Organic Heterojunction Phototransistors Based on Highly Ordered Copper Phthalocyanine/para‐Sexiphenyl Thin Films

High‐performance organic heterojunction phototransistors are fabricated using highly ordered copper phthalocyanine (CuPc) and para ‐sexiphenyl (p ‐6P) thin films. The p ‐6P thin film plays an important role on the performance of CuPc/p ‐6P heterojunction phototransistors. It acts as a molecular template layer to induce the growth of highly ordered CuPc thin film, which dramatically improves the charge transport and decreases the grain boundaries. On the other hand, the p ‐6P thin film can form an effective heterojunction with CuPc thin film, which is greatly helpful to enhance the light absorption and photogenerated carriers. Under 365 nm ultraviolet light irradiation, the ratio of photocurrent and dark current and photoresponsivity of CuPc/p ‐6P heterojunction phototransistors reaches to about 2.2 × 10⁴ and 4.3 × 10² A W^?1, respectively, which are much larger than that of CuPc phototransistors of about 2.7 × 10² and 7.3 A W^?1, respectively. A detailed study carried out with current sensing atomic force microscopy proves that the photocurrent is predominately produced inside the highly ordered CuPc/p ‐6P heterojunction grains, while the photocurrent produced at the boundaries between grains can be neglected. The research provides a good method for fabricating high‐performance organic phototransistors using a combination of molecular template growth and organic heterojunction.     

Multi‐Alternating Organic Semiconducting Films with High Electric Conductivity

High electric conductivity is observed in multilayer stack of m‐MTDATA/F₁₆CuPc. Impedance data shows that the circuit resistance is significantly dropped by three orders of magnitude from ～0.2 MΩ to ～0.4 kΩ when the number of alternating units is increased from one to six, keeping a total thickness of 300 nm. Impedance results show that as the number of alternating units increases, the organic stack shows an increasing capacitance and a decreasing resistance. This result suggests the increasing charges accumulate at the heterojunctions, leading to reduction in overall film resistance. The application of the high conductive units in OLED device results in stability enhancement.     

利用MoO3为电极修饰层的F16CuPc/ CuPc异质结的双极性有机场效应晶体管

在本文中,我们利用钛青铜(CuPc)和氟化钛青铜(F16CuPc)作为空穴传输层和电子传输层的制备了具有异质结结构的有机场效应晶体管(OFETs)。与单层的F16CuPc晶体管相比,异质结结构的晶体管的电子迁移率从3.1×10-3cm2/Vs提高至8.7×10-3cm2/vs,然而,空穴的传输行为却没有被观测到。为了提高空穴的注入能力,我们利用MoO3对源-漏电极进行了修饰,有效地改善了空穴注入。并进一步证实了MoO3的引入使得器件的接触电阻变小,平衡了电子和空穴的注入,从而最终实现了器件的双极性传输。     

Organic Light‐Emitting Transistors Containing a Laterally Arranged Heterojunction

An approach to produce organic light‐emitting transistors (OLETs) containing a laterally arranged heterojunction structure, which minimizes exciton quenching at the metal electrodes, is described. This device configuration provides an organic light‐emitting diode (OLED) structure where the anode (source) electrode, hole‐transport material (field‐effect material), light‐emitting material, and cathode (drain) electrode are laterally arranged, thus offering a chance to control the electroluminescent intensity by changing the gate bias. Pentacene and tris(8‐quinolinolato)aluminum (Alq₃) are employed as the field‐effect and light‐emitting materials, respectively. The laterally arranged heterojunction structures are achieved by successively inclined deposition of the field‐effect and light‐emitting materials. After deposition of pentacene, a narrow gap of about 10–20 nm between the drain electrode and pentacene was obtained, thereby creating an opportunity to fabricate a laterally arranged heterojunction. In the OLETs, unsymmetrical source and drain electrodes, that is, Au and LiF/Al ones, are used to ensure efficient injection of holes and electrons. Visible‐light emission from OLETs is observed under ambient atmosphere. This result is ascribed to efficient carrier injection and transport, formation of a heterojunction, as well as good luminescence from the organic emissive layer. The device structure serves as an excellent model system for OLETs and demonstrates a general concept of adjusting the charge‐carrier injection and transport, as well as the electroluminescent properties, by forming laterally arranged heterojunctions.     

Surface‐Transfer Doping of Organic Semiconductors Using Functionalized Self‐Assembled Monolayers

Controlling charge doping in organic semiconductors represents one of the key challenges in organic electronics that needs to be solved in order to optimize charge transport in organic devices. Charge transfer or charge separation at the molecule/substrate interface can be used to dope the semiconductor (substrate) surface or the active molecular layers close to the interface, and this process is referred to as surface‐transfer doping. By modifying the Au(111) substrate with self‐assembled monolayers (SAMs) of aromatic thiols with strong electron‐withdrawing trifluoromethyl (CF₃) functional groups, significant electron transfer from the active organic layers (copper(II) phthalocyanine; CuPc) to the underlying CF₃‐SAM near the interface is clearly observed by synchrotron photoemission spectroscopy. The electron transfer at the CuPc/CF₃‐SAM interface leads to an electron accumulation layer in CF₃‐SAM and a depletion layer in CuPc, thereby achieving p‐type doping of the CuPc layers close to the interface. In contrast, methyl (CH₃)‐terminated SAMs do not display significant electron transfer behavior at the CuPc/CH₃‐SAM interface, suggesting that these effects can be generalized to other organic‐SAM interfaces. Angular‐dependent near‐edge X‐ray absorption fine structure (NEXAFS) measurements reveal that CuPc molecules adopt a standing‐up configuration on both SAMs, suggesting that interface charge transfer has a negligible effect on the molecular orientation of CuPc on various SAMs.     

Solution‐Deposited Zinc Oxide and Zinc Oxide/Pentacene Bilayer Transistors: High Mobility n‐Channel,Ambipolar, and Nonvolatile Devices

A solution processed n‐channel zinc oxide (ZnO) field effect transistor (FET) was fabricated by simple dip coating and subsequent heat treatment of a zinc acetate film. The field effect mobility of electrons depends on ZnO grain size, controlled by changing the number of coatings and zinc acetate solution concentration. The highest electron mobility achieved by this method is 7.2 cm² V^?1 s^?1 with On/Off ratio of 70. This electron mobility is higher than for the most recently reported solution processed ZnO transistor. We also fabricated bilayer transistors where the first layer is ZnO, and the second layer is pentacene, a p‐channel organic which is deposited by thermal evaporation. By changing the ZnO grain size (or thickness) this type of bilayer transistor shows p‐channel, ambipolar and n‐channel behavior. For the ambipolar transistor, well balanced electron and hole mobilities are 7.6 × 10^?3 and 6.3 × 10^?3 cm² V^?1 s^?1 respectively. When the ZnO layer is very thin, the transistor shows p‐channel behavior with very high reversible hysteresis. The nonvolatile tuning function of this transistor was investigated.     

High‐Performance,Air‐Stable,Top‐Gate,p‐Channel WSe2 Field‐Effect Transistor with Fluoropolymer Buffer Layer

High‐performance, air‐stable, p‐channel WSe₂ top‐gate field‐effect transistors (FETs) using a bilayer gate dielectric composed of high‐ and low‐k dielectrics are reported. Using only a high‐k Al₂O₃ as the top‐gate dielectric generally degrades the electrical properties of p‐channel WSe₂, therefore, a thin fluoropolymer (Cytop) as a buffer layer to protect the 2D channel from high‐k oxide forming is deposited. As a result, a top‐gate‐patterned 2D WSe₂ FET is realized. The top‐gate p‐channel WSe₂ FET demonstrates a high hole mobility of 100 cm²_­ V^?1 s^?1 and a I_ON/I_OFF ratio > 10⁷ at low gate voltages (V_GS ca. ?4 V) and a drain voltage (V_DS) of ?1 V on a glass substrate. Furthermore, the top‐gate FET shows a very good stability in ambient air with a relative humidity of 45% for 7 days after device fabrication. Our approach of creating a high‐k oxide/low‐k organic bilayer dielectric is advantageous over single‐layer high‐k dielectrics for top‐gate p‐channel WSe₂ FETs, which will lead the way toward future electronic nanodevices and their integration.     

Potential barrier and photovoltage at interfaces of hexadecafluoro-copper-phthalocyanine and copper phthalocyanine films on the surface of tin dioxide

Potential barrier formation during the deposition of ultrathin coatings of copper phthalocyanine (CuPc) and hexadecafluoro-copper-phthalocyanine (F₁₆CuPc) on the surface of polycrystalline tin dioxide and during the deposition of F₁₆CuPc coatings over a CuPc film is studied. A photoinduced change in the surface potential of the prepared structures upon exposure to light in the visible wavelength region is detected. The surface photovoltage of the studied organic films has a positive sign with respect to the substrate, its spectral dependences correspond to the absorption spectra of the organic materials CuPc and F₁₆CuPc. Surface potential measurements are performed using a probe beam of low-energy electrons, based on the total current spectroscopy technique. A total decrease in the work function by 0.2 eV is detected during the deposition of a CuPc film up to 8 nm in thickness on a SnO₂ substrate; in the case of the F₁₆CuPc/SnO₂ interface, an increase in the work function by 0.55 eV is detected. At the initial deposition stage, at organic film thicknesses of up to 1.5 nm, the interfacial potential barrier corresponded to electron density transfer from the organic film to the substrate in both cases of CuPc/SnO₂ and F₁₆CuPc/SnO₂. It is assumed that the photoinduced change in the surface potential is caused by charge-carrier separation in a boundary region up to 1.5 nm thick.     

High‐Mobility Air‐Stable Solution‐Shear‐Processed n‐Channel Organic Transistors Based on Core‐Chlorinated Naphthalene Diimides

High charge carrier mobility solution‐processed n‐channel organic thin‐film transistors (OTFTs) based on core‐chlorinated naphthalene tetracarboxylic diimides (NDIs) with fluoroalkyl chains are demonstrated. These OTFTs were prepared through a solution shearing method. Core‐chlorination of NDIs not only increases the electron mobilities of OTFTs, but also enhances their air stability, since the chlorination in the NDI core lowers the lowest unoccupied molecular orbital (LUMO) levels. The air‐stability of dichlorinated NDI was better than that of the tetrachlorinated NDIs, presumably due to the fact that dichlorinated NDIs have a denser packing of the fluoroalkyl chains and less grain boundaries on the surface, reducing the invasion pathway of ambient oxygen and moisture. The devices of dichlorinated NDIs exhibit good OTFT performance, even after storage in air for one and a half months. Charge transport anisotropy is observed from the dichlorinated NDI. A dichlorinated NDI with ?CH₂C₃F₇ side chains reveals high mobilities of up to 0.22 and 0.57 cm² V^?1 s^?1 in parallel and perpendicular direction, respectively, with regard to the shearing direction. This mobility anisotropy is related to the grain morphology. In addition, we find that the solution‐shearing deposition affects the molecular orientation in the crystalline thin films and lowers the d(001)‐spacing (the out‐of‐plane interlayer spacing), compared to the vapor‐deposited thin films. Core‐chlorinated NDI derivatives are found to be highly suitable for n‐channel active materials in low‐cost solution‐processed organic electronics.     

Photoconductivity of C60 as an Origin of Bias‐Dependent Photocurrent in Organic Photovoltaics

The bulk‐ionized photoconductivity of C₆₀ is reported as an origin of the bias‐dependent linear change of the photocurrent in copper phthalocyanine (CuPc)/C₆₀ planar heterojunction solar cells, based on the observation of the variation of the bias‐dependent photocurrent on excitation wavelengths and the thickness‐dependent photocurrent of the C₆₀ layer. A theoretical model, which is a combination of the Braun‐Onsager model for the dissociation of excitons at the donor/acceptor interface and the Onsager model for the bulk ionization of excitons in the C₆₀ layer, describes the bias‐dependent photocurrent in the devices very well. The bulk‐ionized photoconductivity of C₆₀ must generally contribute to the photocurrent in organic photovoltaics, since fullerene and fullerene derivatives are widely used in these devices.     

Solution‐Processable Dithienothiophenoquinoid (DTTQ) Structures for Ambient‐Stable n‐Channel Organic Field Effect Transistors

A series of dialkylated dithienothiophenoquinoids ( DTTQ s), end‐functionalized with dicyanomethylene units and substituted with different alkyl chains, are synthesized and characterized. Facile one‐pot synthesis of the dialkylated DTT core is achieved, which enables the efficient realization of DTTQ s as n‐type active semiconductors for solution‐processable organic field effect transistors (OFETs). The molecular structure of hexyl substituted DTTQ‐6 is determined via single‐crystal X‐ray diffraction, revealing DTTQ is a very planar core. The DTTQ cores form a “zig‐zag” linking layer and the layers stack in a “face‐to‐face” arrangement. The very planar core structure, short core stacking distance (3.30 Å), short intermolecular S? N distance (2.84 Å), and very low lying lowest unoccupied molecular orbital energy level of ?4.2 eV suggest that DTTQ s should be excellent electron transport candidates. The physical and electrochemical properties as well as OFETs performance and thin film morphologies of these new DTTQ s are systematically studied. Using a solution‐shearing method, DTTQ‐11 exhibits n‐channel transport with the highest mobility of up to 0.45 cm² V^?1 s^?1 and a current ON/OFF ratio (I _ON/I _OFF) greater than 10⁵. As such, DTTQ‐11 has the highest electron mobility of any DTT‐based small molecule semiconductors yet discovered combined with excellent ambient stability. Within this family, carrier mobility magnitudes are correlated with the alkyl chain length of the side chain substituents of DTTQ s.     

Improve on/off ratio of organic heterojunction transistors by adopting single-sandwich configuration

Organic heterojunction transistors (OHJTs) based on 5,5′″-bis(naphtha-2-yl)-2,2′:5″,2′″-quaterthiophene (NaT₄)/copper-hexadecafluoro-phthalocyanine (F₁₆CuPc) heterojunction were fabricated in single-sandwich and sandwich configurations, respectively. All the devices operated in depletion-accumulation (normally-on) mode. High field-effect mobility of 0.35 cm²/Vs was obtained for all devices, which was higher than that, 0.20 cm²/Vs of the devices with NaT₄ as active layer. The on/off ratio of 1 × 10⁵ was obtained for OHJTs with single-sandwich configuration, which is three orders of magnitude higher than that of OHJTs with sandwich configuration. Compared with OHJTs with sandwich configuration, the higher on/off ratio was mainly determined by the lower off state current in OHJTs with single-sandwich configuration. In OHJTs with single-sandwich configuration, the well-type shield effect of the source and drain electrodes caused a very narrow empty region in F₁₆CuPc film, which is responsible for the lower off state current.     

Organic Field‐Effect Devices as Tool to Characterize the Bipolar Transport in Polymer‐Fullerene Blends: The Case of P3HT‐PCBM

In organic bulk heterojunction solar cells (oBHJ) the blend morphology in combination with the charge transport properties of the individual components controls the extracted photocurrent. The organic field‐effect transistor (OFET) has been proved as a powerful instrument to evaluate the unipolar carrier transport properties in a wide range of cases. In our work we extend the OFET concept to the evaluation of the bipolar transport properties in polymer‐fullerenes blends and propose a method to improve the accuracy of the evaluation. The method is based on capacitance–voltage (C–V) measurements on MOS structures prepared on the same blends and delivers complementary information on the bulk heterojunction to the one obtained with FETs. The relevance for photovoltaic applications is investigated through the correlation between the current–voltage behavior of solar cells and the bipolar mobility for composites with varying polymer molecular weight and processed from different solvents. In particular the transport features of solar cells produced from o‐Xylene (oX), a non chlorinated solvent more suitable to production requirements, have been compared to the one of devices cast from Chlorobenzene (CB) solution. For the P3HT‐PCBM blend a consistent correlation between the mobility and the electrical fill factor and power performance was found. A significant asymmetry in the bipolar carrier mobility, together with low electron mobility dependent on the M_w value, affects the performances of thick o‐Xylene cast devices. In the case of devices processed from Chlorobenzene the slower carrier has higher mobility and the small electrical losses detected are eventually more related to the formation of space‐charge and eventually to surface recombination. This results in an efficient charge collection that is almost thickness independent. We report a dependence of the slow‐carrier type (electrons or holes) and their mobility on the specific combination of molecular weight and solvent. The mobility data and the solar cell performance coherently fit to the prediction of a device model only based on the drift of carriers under the built‐in electric field originated in the donor‐acceptor oBHJ.     

Direct Patterning of Self‐Assembled Monolayers by Stamp Printing Method and Applications in High Performance Organic Field‐Effect Transistors and Complementary Inverters

Self‐assembled monolayer (SAM) is usually applied to tune the interface between dielectric and active layer of organic field‐effect transistors (OFETs) and other organic electronics, a time‐saving, direct patterning approach of depositing well‐ordered SAMs is highly desired. Here, a new direct patterning method of SAMs by stamp printing or roller printing with special designed stamps is introduced. The chemical structures of the paraffin hydrocarbon molecules and the tail groups of SAMs have allowed to use their attractive van der Waals force for the direct patterning of SAMs. Different SAMs including alkyl and fluoroalkyl silanes or phosphonic acids are used to stamp onto different dielectric surfaces and are characterized by water contact angle, atomic force microscopy, X‐ray diffraction, and attenuated total reflectance Fourier transform infrared. The p‐type dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (DNTT) and n‐type F₁₆CuPc OFETs show competitive mobility as high as 3 and 0.018 cm² V^?1 s^?1, respectively. This stamp printing method also allows to deposit different SAMs on certain regions of same substrate, and the complementary inverter consists of both p‐type and n‐type transistors whose threshold voltages are tuned by stamp printing SAMs and shows a gain higher than 100. The proposed stamp or roller printing method can significantly reduce the deposition time and compatible with the roll‐to‐roll fabrication.     

High‐Performance Phototransistors Based on Single‐Crystalline n‐Channel Organic Nanowires and Photogenerated Charge‐Carrier Behaviors

The photoelectronic characteristics of single‐crystalline nanowire organic phototransistors (NW‐OPTs) are studied using a high‐performance n‐channel organic semiconductor, N,N′‐bis(2‐phenylethyl)‐perylene‐3,4:9,10‐tetracarboxylic diimide (BPE‐PTCDI), as the photoactive layer. The optoelectronic performances of the NW‐OPTs are analyzed by way of their current–voltage (I–V) characteristics on irradiation at different wavelengths, and comparison with corresponding thin‐film organic phototransistors (OPTs). Significant enhancement in the charge‐carrier mobility of NW‐OPTs is observed upon light irradiation as compared with when performed in the dark. A mobility enhancement is observed when the incident optical power density increases and the wavelength of the light source matches the light‐absorption range of the photoactive material. The photoswitching ratio is strongly dependent upon the incident optical power density, whereas the photoresponsivity is more dependent on matching the light‐source wavelength with the maximum absorption range of the photoactive material. BPE‐PTCDI NW‐OPTs exhibit much higher external quantum efficiency (EQE) values (≈7900 times larger) than thin‐film OPTs, with a maximum EQE of 263 000%. This is attributed to the intrinsically defect‐free single‐crystalline nature of the BPE‐PTCDI NWs. In addition, an approach is devised to analyze the charge‐transport behaviors using charge accumulation/release rates from deep traps under on/off switching of external light sources.     

有源层厚度对CuPc-OTFT器件性能的影响

研究了不同厚度有源层的顶电极CuPc-OTFT器件的电学特性。发现器件的性能与有源层厚度有依赖关系，其中，有源层厚度为20nm的器件性能最好。在有源层厚度大于20nm时，有源层厚度的增大不但分去一部分栅电压而且还增大了源、漏电极的接触电阻，从而不利于器件性能的提高。但当有源层厚度小于20nm以后器件的性能开始降低。我们认为当有源层厚度降低到一定程度时，有源层上表面的表面态会使有机材料的隙态浓度增加从而对沟道载流子迁移率产生不良影响以及使器件的阈值电压增大。     

High performance near infrared photosensitive organic field-effect transistors realized by an organic hybrid planar-bulk heterojunction

Compared with organic photodiodes, photoresponsive organic field-effect transistors (photOFETs) exhibit higher sensitivity and lower noise. The performance of photOFETs based on conventional single layer structure operating in the near infrared (NIR) is generally poor due to the low carrier mobility of the active channel materials. We demonstrate a high performance photOFETs operating in NIR region with a structure of hybrid planar-bulk heterojunction (HPBHJ). PhotOFETs with the structures of single layer [lead phthalocyanine (PbPc) or copper phthalocyanine (CuPc)], single planar heterojunction (PHJ) of CuPc/PbPc, double PHJ of CuPc/PbPc/3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and HPBHJ of CuPc/PbPc:PTCDA were fabricated and characterized. It is concluded that the photOFET with HPBHJ structure showed superior performance compared to that with other structures, and for NIR light of wavelength 808 nm, the photOFET with HPBHJ structure exhibited a large photoresponsivity of 322 mA/W, a high external quantum efficiency of around 50%, and a maximal photosensitivity of 9.4 × 10². The high performance of HPBHJ photOFET is attributed to its high exciton dissociation efficiency and excellent hole transport ability. For 50-nm thick CuPc layer, the optimal thickness of the PbPc:PTCDA layer is found to be around 30 nm.     

Interlayer Band‐to‐Band Tunneling and Negative Differential Resistance in van der Waals BP/InSe Field‐Effect Transistors

Atomically thin layers of van der Waals (vdW) crystals offer an ideal material platform to realize tunnel field‐effect transistors (TFETs) that exploit the tunneling of charge carriers across the forbidden gap of a vdW heterojunction. This type of device requires a precise energy band alignment of the different layers of the junction to optimize the tunnel current. Among 2D vdW materials, black phosphorus (BP) and indium selenide (InSe) have a Brillouin zone‐centered conduction and valence bands, and a type II band offset, both ideally suited for band‐to‐band tunneling. TFETs based on BP/InSe heterojunctions with diverse electrical transport characteristics are demonstrated: forward rectifying, Zener tunneling, and backward rectifying characteristics are realized in BP/InSe junctions with different thickness of the BP layer or by electrostatic gating of the junction. Electrostatic gating yields a large on/off current ratio of up to 10⁸ and negative differential resistance at low applied voltages (V ≈ 0.2 V). These findings illustrate versatile functionalities of TFETs based on BP and InSe, offering opportunities for applications of these 2D materials beyond the device architectures reported in the current literature.