Impact of Nanomorphology on Surface Doping of Organic Semiconductors: The Pentacene-C₆₀F₄₈ Interface

Establishing the rather complex correlation between the structure and the charge transfer in organic–organic heterostructures is of utmost importance for organic electronics and requires spatially resolved structural, chemical, and electronic details. Insight into this issue is provided here by combining atomic force microscopy, Kelvin probe force microscopy, photoemission electron microscopy, and low-energy electron microscopy for investigating a case study. We select the interface formed by pentacene (PEN), benchmark among the donor organic semiconductors, and a p-type dopant from the family of fluorinated fullerenes. As for Buckminsterfullerene (C60), the growth of its fluorinated derivative C60F48 is influenced by the thickness and crystallinity of the PEN buffer layer, but the behavior is markedly different. We provide a microscopic description of the C60F48/PEN interface formation and analyze the consequences in the electronic properties of the final heterostructure. For just one single layer of PEN, a laterally complete but noncompact C60F48/PEN interface is created, importantly affecting the surface work function. Nonetheless, from the very beginning of the second layer formation, the presence of epitaxial and nonepitaxial PEN domains dramatically influences the growth dynamics and extremely well packed two-dimensional C60F48 islands develop. Insightful elemental maps of the C60F48/PEN surface spatially resolve the nonuniform distribution of the dopant molecules, which leads to a heterogeneous work function landscape

Hybrid complementary circuits based on p-channel organic and n-channel metal oxide transistors with balanced carrier mobilities of up to 10 cm(2)/Vs

We report the development of hybrid complementary inverters based on p-channel organic and n-channel metal oxide thin-film transistors (TFTs) both processed from solution at 30 V/V) and wide noise margins (70%). The moderate processing temperatures employed and the achieved level of device performance highlight the tremendous potential of the technology for application in the emerging sector of large-area microelectronics

Impact of thin film structure on the pentance C60F48 interface formation and charge transfer

Establishing the rather complex correlation between the structure and the charge transfer in organic–organic heterostructures is of utmost importance for organic electronics and requires spatially resolved structural, chemical, and electronic details. Insight into this issue is provided here by combining atomic force microscopy, Kelvin probe force microscopy, photoemission electron microscopy, and low-energy electron microscopy for investigating a case study. We select the interface formed by pentacene (PEN), benchmark among the donor organic semiconductors, and a p-type dopant from the family of fluorinated fullerenes. As for Buckminsterfullerene (C60), the growth of its fluorinated derivative C60F48 is influenced by the thickness and crystallinity of the PEN buffer layer, but the behavior is markedly different. We provide a microscopic description of the C60F48/PEN interface formation and analyze the consequences in the electronic properties of the final heterostructure. For just one single layer of PEN, a laterally complete but noncompact C60F48/PEN interface is created, importantly affecting the surface work function. Nonetheless, from the very beginning of the second layer formation, the presence of epitaxial and nonepitaxial PEN domains dramatically influences the growth dynamics and extremely well packed two-dimensional C60F48 islands develop. Insightful elemental maps of the C60F48/PEN surface spatially resolve the nonuniform distribution of the dopant molecules, which leads to a heterogeneous work function landscape

Investigation of C60F36 as low-volatility p-dopant in organic optoelectronic devices

We demonstrate highly efficient small molecule organic light emitting diodes and organic solar cells based on the p-i-n-type structure using the fluorinated fullerene molecule C60F36 as p-dopant in the hole transport layer. We present synthesis, chemical analysis, and energy level investigation of the dopant as well as the conductivity of organic layers consisting of a matrix of N,N,N′,N′-tetrakis 4-methoxyphenyl-benzidine(MeO-TPD) or N,N′-[(Diphenyl-N,N′-bis)9,9,-dimethyl-fluoren-2-yl]-benzidine(BF-DPB) doped by the fullerene compound. State of the art organic p-i-n devices containing C60F36 show efficiencies comparable to devices with the commonly used p-dopant2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). The advantages of the fullerene based dopant are the low volatility and high thermal stability, which is beneficial for device operation under elevated temperature. These properties make C60F36 highly attractive for the usage as p-dopant in a broad spectrum of organic p-i-n devices like organic light emitting diodes, solar cells, memories, or transistors. © 2011 American Institute of Physics.</p

Hall Effect in Polycrystalline Organic Semiconductors: The Effect of Grain Boundaries

Highly crystalline thin films in organic semiconductors are important for applications in high-performance organic optoelectronics. Here, the effect of grain boundaries on the Hall effect and charge transport properties of organic transistors based on two exemplary benchmark systems is elucidated: (1) solution-processed blends of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C-8-BTBT) small molecule and indacenodithiophene-benzothiadiazole (C16IDT-BT) conjugated polymer, and (2) large-area vacuum evaporated polycrystalline thin films of rubrene (C42H28). It is discovered that, despite the high field-effect mobilities of up to 6 cm(2) V-1 s(-1) and the evidence of a delocalized band-like charge transport, the Hall effect in polycrystalline organic transistors is systematically and significantly underdeveloped, with the carrier coherence factor alpha < 1 (i.e., yields an underestimated Hall mobility and an overestimated carrier density). A model based on capacitively charged grain boundaries explaining this unusual behavior is described. This work significantly advances the understanding of magneto-transport properties of organic semiconductor thin films.11Nsciescopu

Small Molecule/Polymer Blend Organic Transistors with Hole Mobility Exceeding 13 cm²V⁻¹s⁻¹

A ternary organic semiconducting blend composed of a small-molecule, a conjugated polymer, and a molecular p-dopant is developed and used in solution-processed organic transistors with hole mobility exceeding 13 cm(2) V(-1) s(-1) (see the Figure). It is shown that key to this development is the incorporation of the p-dopant and the formation of a vertically phase-separated film microstructure

14 GHz schottky diodes using a p-doped organic polymer.

The low carrier mobility of organic semiconductors and the high parasitic resistance and capacitance often encountered in conventional organic Schottky diodes, hinder their deployment in emerging radio frequency (RF) electronics. Here we overcome these limitations by combining self-aligned asymmetric nanogap electrodes (∼25 nm) produced by adhesion-lithography, with a high mobility organic semiconductor and demonstrate RF Schottky diodes able to operate in the 5G frequency spectrum. We used C16 IDT-BT, as the high hole mobility polymer, and studied the impact of p-doping on the diode performance. Pristine C16 IDT-BT-based diodes exhibit maximum intrinsic and extrinsic cutoff frequencies (fC ) of >100 and 6 GHz, respectively. This extraordinary performance is attributed primarily to the planar nature of the nanogap channel and the diode's small junction capacitance (100 and ∼14 GHz respectively, while the DC output voltage of a RF rectifier circuit increases by a tenfold. Our work highlights the importance of the planar nanogap architecture and paves the way for the use of organic Schottky diodes in large-area radio frequency electronics of the future. This article is protected by copyright. All rights reserved