Morphology Optimization for the Fabrication of High Mobility Thin‐Film Transistors

Wang

et al. 2016

Adv Elect Materials

both p-type and n-type OFETs. Based on the hybrid dielectrics, the operating gate bias ( V GS ) for the pentacene-based and N,N′ -ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C 13 H 27 )-based OFETs is down to −2 and 2 V, respectively. The devices exhibit typical µ FE , high ON/OFF ratio, and, in particular, excellent bias stress stability upon prolonged operation up to 6 × 10 4 s. The presence of the sputtered C NPs turns out to be the key for the formation of an ultrathin and pinhole-free polymer dielectric layer. This type of low-voltage OFETs with high operating stability can be realized on a fl exible substrate as well. Therefore, depositing an ultrathin low-k polymer on sputtered C NPs is a promising way for achieving high-performance low-voltage OFETs.The device structure of the low-voltage OFETs is schematically illustrated in Figure 1 , where a submonolayer of C is deposited by sputtering and spontaneously forms C NPs on Si. [ 23 ] The atomic force microscopy (AFM) image in Figure 1 demonstrates the uniform distribution of a number of C NPs on the substrate, and their height and lateral size are around 2 and 20 nm, respectively. The X-ray photoelectron spectroscopy (XPS) and Raman characterization results ( Figure S1, Supporting Information) suggest that the sputtered C NPs are amorphous C containing oxygenated groups and small graphite-like domains. [ 23 ] The C-NP-modifi ed Si surface possesses high surface energy and induces a small water contact angle of 45° (Figure 1 ), and the surface roughness is slightly increased from 0.17 ± 0.03 to 0.24 ± 0.03 nm upon the deposition of C NPs. Three kinds of low-k polymers, i.e., polystyrene (PS), polymethylmethacrylate (PMMA), and poly(2-vinyl naphthalene) (PVN), are then spin-coated onto the sputtered C NPs as the gate dielectrics (PS/C, PMMA/C, and PVN/C, respectively). The preparation conditions are controlled to deposit the dielectric layers as thin as 12-13 nm. Measured C i for the PS/C, PMMA/C, and PVN/C dielectrics ( Figure S2a,b, Supporting Information), about 180, 230, and 205 nF cm −2 , respectively, are quite large owing to their small d . Note that experimentally derived C i are well consistent with the theoretical ones calculated from k / d . For such ultrathin low-k dielectrics, the accumulated surface charge density ( n = C i V GS / q ) can be up to the order of 10 12 cm −2 at V GS = ±1 V, where q is the electron charge quantity. The pentacene/PTCDI-C 13 H 27 thin fi lm acts as the p-type/n-type organic active layer, respectively, and Cu on top is employed as the drain and source electrodes. [ 24 ] Figure 2 a-c shows the transfer characteristics of the pentacene-based low-voltage OFETs on the PS/C, PMMA/C, and PVN/C dielectrics, respectively, where the drain bias ( V DS ) is as low as −0.2 V and the V GS range is no higher than −2 V. I GS Organic fi eld-effect transistors (OFETs) are essential components in future fl exible, wearable, and portable electronic devices, which have numerous applications such as sensors, identifi cation ...

Section: Doi: 101002/aelm201500349mentioning

confidence: 96%

Bias‐Stress‐Stable Low‐Voltage Organic Field‐Effect Transistors with Ultrathin Polymer Dielectric on C Nanoparticles

Wang

et al. 2016

Adv Elect Materials

“…22,28,29 In contrast, the hydrophobic layer on top can repel water molecules from the dielectric surface, and it could be favorable for the ordered growth of the organic polycrystalline active layers. 11,30 As a consequence, both the p-type and n-type OFETs based on the bilayer dielectrics possess the much enhanced operational stability, as demonstrated in Figs. 3(a) and 3(b), respectively.…”

mentioning

confidence: 89%

Operational stability enhancement of low-voltage organic field-effect transistors based on bilayer polymer dielectrics

She

Applied Physics Letters

Zhang

et al. 2013

“…The periodic calculations of the electron-accepted TAPI single-crystal validate that MO simulations of the electron-accepted states is more realistic to evaluate electrical conductivity of vdW&Clb-induced molecular integrations than the band theory simulation of the periodic single crystal structure. Theoretical interpretation of SOMO-based conductivity of solidstate sumanene, 33 pentacene, 34 and perovskite (N(CH 3 ) 4 + PbI 3 − ) 35 is in progress in view of DFT-based molecular modeling of their electron-accepted states.…”

Section: Discussionmentioning

confidence: 99%

Molecular Orbital-Based Verification of Conductivity of Tetramethylammonium Pentaiodide and Pentaiodide-Based Electrolytes in Dye-Sensitized Solar Cells

Yanagida

Yanagisawa

Segawa

2015

J. Electrochem. Soc.

In order to verify the electrical conductivity of tetramethylammonium pentaiodide (TAPI, I 5 − (N(CH 3 ) 4 + )) crystal, molecular orbital configurations and energy structures of the electron-carrying state TAPI packing unit (TAPI-6) are examined by density functional theory (DFT). The narrow energy gap of the electron-carrying state radical anion of .− proves the semi-conductivity of TAPI together with the aligned configuration of singly occupied molecular orbital (SOMO) and the spin density distribution on SOMO. The molecular orbital analysis of the electron-accepted states of the vertical fragment unit of .− and the coplanar fragment unit of .− rationalize the anisotropic semiconducting property in TAPI. DFT-based molecular modeling for molecular integration of + I 3 − ] n . Additionally, the conductivity of TAPI is higher (about seven times) at the direction perpendicular to the coplanar aligned I 5 − components than at the direction parallel to the I 5 − -components. 1 A recent X-ray crystallography analysis of TAPI provided the precise structure of the TAPI crystal, and the packing unit structure, [N(CH 3 ) 4 + I 5 − ] 6 (TAPI-6) becomes available for DFT-based molecular orbital modeling.2 Molecular orbital (MO) structures of TAPI-6, the vertical fragment of (N(CH 3 ) 4 + I 5 − ) 4 (TAPI-4) and the coplanar fragment of (N(CH 3 ) 4 + I 5 − ) 3 (TAPI-3) in TAPI-6, are obtained by DFT-based single point calculations and examined in view of MO configuration and energy levels for interpretation of the anisotropic conductivity of TAPI (Fig. 1).With regard to the MO verification of electrical conductivity, band conduction, 3 hopping conduction, 4 and polaron conduction models were proposed. 5,6 The high charge mobility of organic semiconductor crystals was discussed using the hoping or the band model.7 By using the semi-classical dynamics and parameters obtained with the density functional theory (DFT) MO calculation of a single molecule or a molecular dimer, the hopping or the polaron model successfully described the high hole mobility of the organic semiconductors at room temperature. [8][9][10] One of the authors investigated the highest mobility of crystalline rubrene in view of the band dispersion, 11 and the electronic properties of methylammonium lead iodide perovskite [CH 3 NH 3 + PbI 3 − ] were discussed on the basis of effective masses of electrons and holes in the ambipolar transport. 12 As for the present MO-based verification of electrical conductivity, we took into consideration that the conductivity is observable under bias conditions and become dominant at electron-accepted states. Then, the molecular integrated systems that are interacting one another via van z