Fluorinated Dielectrics‐Modulated Organic Phototransistors and Flexible Image Sensors

Abstract

gathered lots of attention due to gate tunability and signal amplification for flexible active-matrix sensing. [8][9][10] In the previous studies of OPTs, the interface engineering of polymeric dielectrics offers an effective approach to modulate the performance of the devices. [11][12][13] As one of the representatives of polymeric dielectrics for modulation, aromatic polyimide (PI) has become a promising candidate for gate dielectric layer with good feasibility for fabrication of organic electronic devices due to its excellent thermal stability, chemical resistance, and mechanical flexibility. [14][15][16][17] However, in our previous work, we found that the weak van der Waals interaction between the PI (KAPTON) chains led to a flat 2D structure at the interface resulting in the disorder molecular stacking of planar molecules for low mobility. [18] To this end, the functionalization of PI with selfassembly monolayer could improve the mobility by an order of magnitude with a value up to 0.462 cm 2 V −1 s −1 . [19] Besides, the incorporation of fluorine functional groups into PI molecules will enhance its surface hydrophobicity and reduce the surface energy of the interface. [20][21][22] Furthermore, due to the chemical inertia, hydrophobicity, and low polarizability of CF bond, the adsorption of water and oxygen molecules in the air can be inhibited by fluorinated PI, resulting in the reduction of the polarity of It is generally believed that the incorporation of fluorine functional groups into dielectrics can effectivelyimpede the charge-trapping process and improve carrier mobility. However, the relationship between the device performance and fluorinated groups is still not clear and also the modulation effect of fluorine functional groups on photogenerated charge carrier in phototransistors has not yet been investigated. Herein, phototransistors are constructed by using three kinds of gate dielectric layers with different fluorinated groups to exploit the effect of fluorine functional groups. It is concluded that the presence of fluorinated groups indeed increases the transistor mobility and optical figures of merit in phototransistors compared to the device with a fluorine-free dielectric layer. Concurrently, the exciton binding energy is increased with the addition of fluorinated groups, resulting in the decrease of phototransistor performance compared with less content of fluorinated groups due to the synergistic balance effect of fluorine functional groups. The results further clarify how the fluorine functional groups optimize the interface of organic phototransistors and modulate the photoelectric performance.

Optimization of Alkyl Side Chain Length in Polyimide for Gate Dielectrics to Achieve High Mobility and Outstanding Operational Stability in Organic Transistors

“…Polyimide (PI) and its derivatives have received more attention as dielectric materials for application in OTFTs because of their adjustable structures, good mechanical flexibility, excellent insulating property, higher temperature resistance, suitability for large-area fabrication, and lower cost. − For instance, Park et al reported that the low surface energy of PI gate dielectrics could improve the mobility of OTFTs from 0.11 to 0.56 cm 2 /Vs compared to PI with high surface energy, which was achieved by controlling siloxane groups with different weights and content levels to modify the PI backbone structure. Recently, Ji and co-workers found that the self-rippled structure of commercialized Kapton-PI’s precursor (PAA) containing the strong polar groups (−COOH and −CONH) allow more desirable organic semiconductor arrangement on its surface for higher OTFT mobility and lower operational voltage.…”

Recent Progress in Fluorinated Dielectric‐Based Organic Field‐Effect Transistors and Applications

“…[109] For optical performance, the synergistic balance effect induced by fluorine atoms is dominant in the fluorinated dielectric layer devices. [134] What's more, the positive shift (relative to zero bias) of threshold voltage is normally observed in p-type transistors, which would further limit their applications in organic integrated circuits. [157][158][159] In addition, the development of fluorinated polymer dielectrics still needs to be paid more attention to improve the mobility of the devices.…”

“…fluorine-free PI, ODA-6FDA PI with -2CF 3 , and TFMB-6FDA PI with ─4CF 3 , respectively (Figure 11a). [134] The X-ray diffraction (XRD) characterization was performed to study the crystalline properties of the DNTT films deposited on different dielectrics. It was clearly observed that DNTT films deposited on fluorinated PI dielectric layer exhibited a higher intensity than those on pure PI (Figure 11b) and more of ─CF 3 contributed to the higher crystallinity and higher ordered molecular stacking.…”

“…o) Current mapping of the 4 × 4 imaging matrix under illumination with "U" type mask (1.5 cm × 1.5 cm) on top. Reproduced with permission [134]. Copyright 2022, Wiley-VCH.…”

High‐Performance Organic Phototransistors Based on Single‐Crystalline Microwire Arrays

“…The efficient detection of optical information plays an important role in modern science and technology. [1][2][3][4][5][6] With the advantages of tunable bandgap, mechanical flexibility, and low-cost and solution-processing manufacturing of organic semiconductor DOI: 10.1002/adsr.202300169 materials served as photoactive layers, organic photodetectors have attracted considerable attention and showing great potential in next-generation image sensors, health monitoring, quantum communication, biomedical sensing and so on. [7][8][9][10][11][12][13][14][15] As a typical photo-sensor for highly sensitive photodetection, OPTs in which the channel carrier density can be effectively modulated by both gate voltage and incident light, [16][17][18] exhibit higher sensitivity, intrinsic amplification, and lower dark currents compared with the traditional two-terminal photodiodes, thus boosting a series of advanced research.…”