An official website of the United States government
Abstract Atomically thin 2D materials are good templates to grow organic semiconductor thin films with desirable features. However, the 2D materials typically exhibit surface roughness and spatial charge inhomogeneity due to nonuniform doping, which can affect the uniform assembly of organic thin films on the 2D materials. A hybrid template is presented for preparation of highly crystalline small‐molecule organic semiconductor thin film that is fabricated by transferring graphene onto a highly ordered self‐assembled monolayer. This hybrid graphene template has low surface roughness and spatially uniform doping, and it yields highly crystalline fullerene thin films with grain sizes >300 nm, which is the largest reported grain size for C60thin films on 2D materials. A graphene/fullerene/pentacene phototransistor fabricated directly on the hybrid template has five times higher photoresponsivity than a phototransistor fabricated on a conventional graphene template supported by a SiO2wafer.
more »
« less
Readily Tunable Surface Potential by Functionalizing Pentacene with Dipole Monolayers
Abstract The surface potential of a prototypical organic semiconductor, pentacene, is chemically modified by the addition of a dipole monolayer on top of the thin film. Changes are afforded by reacting the topmost layer of pentacene to generate the monolayer, and the reactant structure provides a high degree of tunability for surface potential, with shifts up to 800 mV possible. Despite the complexity of the adsorbed layer, the surface potential shift displays a near‐linear dependency between dipole strength and surface potential change, and a good degree of predictability via the Helmholtz equation. The large changes in surface potential should be enough to access electron injection in thisp‐type semiconductor, but deviceI–Vcharacteristics are not consistent with this behavior. Interactions between the metal top contact and a chemical functional group within the monolayer are the likely culprit, with spectroscopic evidence presented. While tailoring the surface potential of organic surfaces is achievable, maintaining the integrity of surface energetics upon metal deposition remains challenging.
more »
« less
- Award ID(s):
- 1956202
- PAR ID:
- 10641061
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Electronic Materials
- Volume:
- 11
- Issue:
- 7
- ISSN:
- 2199-160X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract 2D semiconductors such as monolayer molybdenum disulfide (MoS2) are promising material candidates for next‐generation nanoelectronics. However, there are fundamental challenges related to their metal–semiconductor (MS) contacts, which limit the performance potential for practical device applications. In this work, 2D monolayer hexagonal boron nitride (h‐BN) is exploited as an ultrathin decorating layer to form a metal–insulator–semiconductor (MIS) contact, and an innovative device architecture is designed as a platform to reveal a novel diode‐like selective enhancement of the carrier transport through the MIS contact. The contact resistance is significantly reduced when the electrons are transported from the semiconductor to the metal, but is barely affected when the electrons are transported oppositely. A concept of carrier collection barrier is proposed to interpret this intriguing phenomenon as well as a negative Schottky barrier height obtained from temperature‐dependent measurements, and the critical role of the collection barrier at the drain end is shown for the overall transistor performance.more » « less
-
Abstract Polymer ferroelectrics are playing an increasingly active role in flexible memory application and wearable electronics. The relaxor ferroelectric dielectric, poly(vinylidene fluoride trifluorethylene (PVDF‐TrFE), although vastly used in organic field‐effect transistors (FETs), has issues with gate leakage current especially when the film thickness is below 500 nm. This work demonstrates a novel method of selective poling the dielectric layer. By using solution‐processed 6,13‐bis(triisopropylsilylethynyl)pentacene (TIPS‐pentacene) as the organic semiconductor, it is shown that textured poling of the PVDF‐TrFE layer dramatically improves FET properties compared to unpoled or uniformly poled ferroelectric films. The texturing is achieved by first vertically poling the PVDF‐TrFE film and then laterally poling the dielectric layer close to the gate electrode. TIPS‐pentacene FETs show on/off ratios of 105and hole mobilities of 1 cm2Vs−1under ambient conditions with operating voltages well below −5 V. The electric field distribution in the dielectric layer is simulated by using finite difference time domain methods.more » « less
-
Abstract Reducing the Schottky barrier height and Fermi level de‐pinning in metal‐organic semiconductor contacts are crucial for enhancing the performance of organic transistors. The reduction of the Schottky barrier height in bottom‐contact top‐gate organic transistors is demonstrated by adding 1 nm thick atomic layer deposited Al2O3on the source and drain contacts. By using two different donor‐acceptor copolymers, bothp‐andn‐type transistors are investigated. Temperature‐dependent current–voltage measurements from non‐treated, self‐assembled monolayer treated, and Al2O3treated Au source‐drain contact field‐effect transistors with varying channel lengths are carried out. The drain current versus drain voltage near zero gate voltage, which may be described by the thermionic emission model at temperatures above 150 K, allows the estimation of the Schottky barrier height (φB). The Al2O3contact‐treated transistors show more than 40% lowerφBcompared with the non‐treated contacts in thep‐type transistor. Similarly, an isoindigo‐based transistor, withn‐type transport, shows a reduction inφBwith Al2O3treated contacts suggesting that such ultrathin oxide layers provide a universal method for reducing the barrier height.more » « less
-
Abstract A dual‐layer interphase that consists of an in‐situ‐formed lithium carboxylate organic layer and a thin BF3‐doped monolayer Ti3C2MXene on Li metal is reported. The honeycomb‐structured organic layer increases the wetting of electrolyte, leading to a thin solid electrolyte interface (SEI). While the BF3‐doped monolayer MXene provides abundant active sites for lithium homogeneous nucleation and growth, resulting in about 50% reduced thickness of inorganic‐rich components among the SEI layer. A low overpotential of less than 30 mV over 1000 h cycling in symmetric cells is received. The functional BF3 groups, along with the excellent electronic conductivity and smooth surface of the MXene, greatly reduce the lithium plating/stripping energy barrier, enabling a dendrite‐free lithium‐metal anode. The battery with this dual‐layer coated lithium metal as the anode displays greatly improved electrochemical performance. A high capacity‐retention of 175.4 mAh g−1at 1.0 C is achieved after 350 cycles. In a pouch cell with a capacity of 475 mAh, the battery still exhibits a high discharge capacity of 165.6 mAh g−1with a capacity retention of 90.2% after 200 cycles. In contrast to the fast capacity decay of pure Li metal, the battery using NCA as the cathode also displays excellent capacity retention in both coin and pouch cells. The dual‐layer modified surface provides an effective approach in stabilizing the Li‐metal anode.more » « less
