Fabrication of Ti₃C₂T_x MXene Transparent Thin Films with Tunable Optoelectronic Properties

Abstract

properties of novel transparent electrode materials include high transmittances (>85%) in the UV and visible regions and low sheet resistances ( R s ), in the range of 0.01-1 kΩ sq −1 . In addition, the new materials should be mechanically robust for fl exible touch screen and organic lightemitting diode applications. On top of excellent optoelectronic and mechanical properties, low cost of production per unit area and feasibility of large-scale fabrication are key factors determining their industrial success. [ 1a , 2 ] Among numerous materials being considered for transparent electrode applications, 2D graphene is arguably the most studied in the past few years. [ 1e , 3 ] Transparent conductive graphene fi lms are mainly produced by two methods: direct chemical vapor deposition (CVD) or solution-processing of reduced graphene oxide (rGO). [ 4 ] Although the CVD method results in high-performance fi lms, their high fabrication cost and size limitations have hindered their commercialization. Several solution-processing methods, such as spray coating, spin coating, and dip coating, have also been employed to fabricate thin fi lms from rGO solutions. [ 5 ] However, the transparent fi lms produced by such methods exhibit high R s (1-1000 kΩ sq −1 ), mainly due to defects (functional groups) and inter-fl ake resistance. [ 6 ] The development of novel materials for transparent conductive fi lms and suitable methods for their large-scale and low-cost production remains a challenge.Recently, a new class of 2D transition metal carbides and/or nitrides, so-called MXenes, was discovered. [ 7 ] Both theoretical and experimental results indicate that most MXenes exhibit metallic conductivity, hydrophilicity, high mechanical strength, and can act as intercalation hosts. [ 8 ] They have shown great promise as electrodes in supercapacitors, Li-ion and other types of batteries, fuel cells, reinforcement for polymers, adsorbents, and sensors. [ 9 ] Upon delamination, colloidal MXene solutions contain large quantities of ≈1 nm-thick 2D fl akes with lateral sizes up to several micrometers, which are perfect for solution processing.

Transparent, conductive solution processed spincast 2D Ti2CTx (MXene) films

“…Since the discovery of single-layered graphene and its remarkable properties, there has been a groundswell of interest in two-dimensional, 2D, materials [1][2][3][4][5][6][7][8][9][10][11]. The desirable optical and electronic behavior resulting from reduced dimensionality is even further enriched by the opportunity for co-assembly of different 2D materialtypes to form novel heterojunctions [12].…”

“…To date all work in this area has focused on Ti 3 C 2 T x [8,9,31,32]. Herein, we start to probe the importance of MXene chemistry on the optoelectronic properties of spincast films from aqueous colloidal solutions.…”

“…Ag-nanowires [27] are a good example of non-uniform type. Examples of the former include, un-doped [28] and doped graphene [29,30], MXenes [8,9,31,32] and the industry standard indium tin oxide, ITO. While the combination of transparency and conductivity of ITO is in general difficult to surpass, the high cost and limited supply of indium have energized efforts, especially in the 2D community, to find alternatives.…”

“…If the films are thin enough, they are also transparent [8,9,31,32]. For quantitative comparison of transparent conductors, we use a common figure of merit (FOM), defined as the ratio of the DC conductivity, σ DC , to a quantity termed the 'optical conductivity', σ OP , derived from the optical transmittance [33].…”

Electrophoretic Deposition of Two-Dimensional Titanium Carbide (MXene) Thick Films

“…These colloidal dispersions have been shown to consist of individual and fewlayer MXene sheets. 14 To date, it has been demonstrated that MXene solids can be assembled from colloids by vacuum filtration, 38 spincoating, 30,41 spray coating, 31 spray drying, 40 and electrospraying. 42 Herein we explored EPD as a high-throughput synthesis route for MXene films.…”