Fabrication of Wafer-Scale Organic Single-Crystal Films with Uniform In-Plane Orientation via Wetting-Assisted In-Air Sublimation for High-Performance Transistor Arrays

Abstract

The production of single-crystalline organic thin films on a large scale is challenging but imperative for industrial applications of organic electrics. This work improves a vapor-based method on the basis of our recently invented microspacing in-air sublimation (MAS) to achieve wafer-scale uniform single-crystalline organic films. The method alters the wettability of both the bottom and top substrates in MAS. By virtue of the vapor-to-melt-to-crystal process and the unique genetic relationship between the morphology of source materials and that of the grown crystals, wettability control on the one hand promotes the dispersion of the molten source materials and on the other hand drives the liquid crystal phase on the top substrate to form uniform single-crystalline films over the whole substrate. Using 2,7-dioctyl[1]­benzothieno­[3,2-b]­[1]­benzothiophene (C8-BTBT) as an example, centimeter-sized crystalline films with pure orientations are achieved. Transistor arrays fabricated on the crystalline films exhibit high yield and uniform performance with an average mobility of 3.91 cm2 V–1 s–1. This method provides an opportunity to realize vapor-grown single-crystalline films but not random and discrete single crystals via physical vapor transport nor the amorphous/polycrystalline films via vacuum deposition, which may be a step toward future commercialization of organic electronics.

Homogeneously Oriented Organic Single‐Crystalline Patterns Grown by Microspacing In‐Air Sublimation

“…The crystallization capacities along a or b directions are less differentiating; however, due to the larger molecular packing overlap in a direction, the charge transporting ability along a ‐axis is about four to six times higher than that along b ‐axis according to our previous discoveries. [ 32 ] Such anisotropic characteristic makes it essential to manipulate the growth direction of the patterns along the closest packing a ‐axis, on the one hand to excavate the material's best‐performance, and on the other hand to avoid device performance inconsistency.…”

“…The growth procedure is similar to that in our previous work, [ 32 ] wherein a totally O 2 plasma treated silicon wafer was employed as the bottom substrate and the above‐mentioned substrate with patterned surface acting as the growth substrate was laid above the bottom substrate with a spacing distance of about 300 µm separated by a glass square ring. The grounded C8‐BTBT powders (about 50 µg) were placed on the bottom substrate as source materials.…”

“…As has been revealed in our last work, the molten C8‐BTBT liquid is complete wetting on the O 2 plasma surface while nonwetting on the OTS‐treated surface. [ 32 ] At the growth temperature of 150 °C, the C8‐BTBT powders melted into a liquid film covering the entire surface of the bottom substrate, which is in favor of uniform mass transport. Because of the wettability difference, the vaporized molecules deposited on the down surface of the top substrate would be pinned in the wettable O 2 plasma treated area, resulting patterned C8‐BTBT crystals at designed positions.…”

Vapor‐Phase Growth Strategies of Fabricating Organic Crystals for Optoelectronic Applications

“…Besides, an OFET device array was prepared by a 2,7‐dioctyl[1]‐benzothieno[3,2‐ b ][1]benzothiophene (C8‐BTBT) film produced on an O 2 plasma‐treated substrate. [ 138 ] The schematic diagram of the device is shown in Figure 16j as well as the optical microscopy image of the array composed of 5 × 7 OFETs is displayed in Figure 16k. These devices have the same structure as the previous ones.…”

Morphology dependent light-induced photoluminescence enhancement of CsPbBr3 microcrystals

“…The growth of the CsPbBr 3 was carried out in a MAS setup similar to those in our previous work. [16][17][18][19][20] First, the grounded CsPbBr 3 powders as the source materials (approximately tens of micrograms) were placed on the hotplate. Then the growth substrate (silica/sapphire) lied above the source materials with a micro space of 300 mm defined by the glass square rings.…”