Switching from Electron to Hole Transport in Solution-Processed Organic Blend Field-Effect Transistors

Abstract

Organic electronics became an attractive alternative for practical applications in complementary logic circuits due to the unique features of organic semiconductors such as solution processability and ease of large-area manufacturing. Bulk heterojunctions (BHJ), consisting of a blend of two organic semiconductors of different electronic affinities, allow fabrication of a broad range of devices such as light-emitting transistors, light-emitting diodes, photovoltaics, photodetectors, ambipolar transistors and sensors. In this work, the charge carrier transport of BHJ films in field-effect transistors is switched from electron to hole domination upon processing and post-treatment. Low molecular weight n-type N,N′-bis(n-octyl)-(1,7&1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI8-CN2) was blended with p-type poly[2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14) and deposited by spin-coating to form BHJ films. Systematic investigation of the role of rotation speed, solution temperature, and thermal annealing on thin film morphology was performed using atomic force microscopy, scanning electron microscopy, and grazing incidence wide-angle X-ray scattering. It has been determined that upon thermal annealing the BHJ morphology is modified from small interconnected PDI8-CN2 crystals uniformly distributed in the polymer fraction to large planar PDI8-CN2 crystal domains on top of the blend film, leading to the switch from electron to hole transport in field-effect transistors.

Electron-to Hole Transport Change Induced by Solvent Vapor Annealing of Naphthalene Diimide Doped with Poly(3-Hexylthiophene)

“…It is also unclear if packing of NDIC8 molecules in the new crystal phase can be the reason behind changing the charge transport mode from n-type to p-type. Similar example of "switching" from electron to hole transport was reported for the thermally annealed blend of poly {2,5-bis(3tetradecylthiophene-2-yl)thieno [3,2-b]thiophene} (PBTTT) with one of perylene diimide (PDI) derivatives mixed at the 1:1 ratio (Fidyk et al, 2020). The change in the charge transport mode in the PBTTT:PDI blend was attributed to a morphological change caused by thermally-induced crystal growth and a consequent phase separation during the thermal annealing.…”

“…Our results suggest that formation of the new crystal system was based on nucleation and growth. Such a recrystallization mechanism is different than typically reported Ostwald-ripening-based growth of crystal domains in the film (Chlebosz et al, 2017;Fidyk et al, 2020). The crystal structure of needles forming the NDIC8:P3HT dendritic morphology was not previously reported in the literature and requires further studies.…”

“…Either heterogeneous nucleation or epitaxial growth may cause formation of metastable film morphologies that can be kinetically equilibrated by thermal or solvent vapor annealing (Chlebosz et al, 2020;Mori et al, 2020). Both kinds of annealing cause profound changes in film morphology (Schulz and Ludwigs 2017;Chlebosz et al, 2020;Fidyk et al, 2020). Solvent vapor annealing is process substantially longer than the film deposition.…”

Polyferrocenylsilane Semicrystalline Polymer Additive for Solution-Processed p-Channel Organic Thin Film Transistors

“…Polymeric materials as additives have rapidly attracted considerable attention for application in organic electronics [ 1 , 2 , 3 , 4 , 5 ]. When they are blended with organic semiconductors, those polymers demonstrate various merits in controlling the crystal growth, enhancing the semiconductor morphology, and improving the electrical performance of organic thin film transistors (OTFTs) [ 6 , 7 ]. Research efforts in the semiconductor/polymer blend systems primarily focused on various amorphous polymers such as poly(α-methylstyrene) (PαMS) [ 8 , 9 ], polymethyl methacrylate (PMMA) [ 10 , 11 ], and polystyrene (PS) [ 12 , 13 ].…”

Electrodeposited Copolymers Based on 9,9′-(5-Bromo-1,3-phenylene)biscarbazole and Dithiophene Derivatives for High-Performance Electrochromic Devices

“…Organic conjugated polymers have attracted more attention over the past two decades owing to their versatile applications in energy-stored devices [ 1 , 2 ], electrochromic devices [ 3 , 4 , 5 , 6 , 7 ], sensors [ 8 , 9 , 10 ], catalysts [ 11 , 12 , 13 ], solar cells [ 14 , 15 ], field effect transistors [ 16 , 17 ], and light-emitting diodes [ 18 , 19 , 20 ]. Today, many practical applications of electrochromic technologies, including self-tunable eyewear, auto-dimmer rearview mirrors, smart textiles, and electronic paper, are presented in our daily lives [ 21 , 22 ].…”