One-Way Continuous Deposition of Monolayer MXene Nanosheets for the Formation of Two Confronting Transparent Electrodes in Flexible Capacitive Photodetector

Abstract

MXenes based on titanium carbide are promising next-generation transparent electrode materials due to their high metallic conductivity, optical transparency, mechanical flexibility, and abundant hydrophilic surface functionality. MXene electrodes offer a much wider conductive surface coverage than metal nanowires, thereby gaining popularity as flexible electrode materials in supercapacitors and energy devices. However, given that monolayer MXene nanosheets are only a few nanometers thick, meticulous surface treatments and deposition technologies are required for a practical implementation of these transparent electrodes. Unfortunately, a capacitor produced by forming high-quality transparent MXene electrodes on both sides of a film has not yet been reported. We report the successful development of a one-way continuous deposition technology to form high-quality MXene nanosheet-based transparent electrodes on both surfaces of a polymer film without large physical stresses on the MXene nanosheets. One transparent electrode was formed by transferring MXene nanosheets predeposited on a temporary glass substrate to the film surface, while the other was directly deposited on the exposed film surface. The Ti3AlC2 precursor (MAX) was synthesized via a spark plasma sintering crystallization, and the MXene nanosheets were prepared via a subsequent Al-selective etching and delamination. We used this material to implement a capacitive photodetector consisting of two layers of opposing transparent electrodes. The flexible photodetector was based on poly­(vinyl butyral) (PVB), which was solidly bonded with MXene nanosheets to serve as a free-standing binder for the Cu-doped ZnS semiconductor particles. The fabricated device exhibited excellent mechanical stability due to the high affinity between the MXene nanosheets and PVB. Furthermore, the device exhibited an initial capacitance of 2 nF, photosensitivity of 12.5 μF/W, and rise and decay times of 0.031 and 0.751 s, respectively. All these parameters were 1 to 2 orders of magnitude higher or faster than reported capacitive photodetectors. Overall, the proposed approach resolves the core issues associated with existing metal nanowire-based electrodes, and it is a breakthrough in the development of next-generation flexible devices comprising two layers of confronting transparent electrodes.

High‐Performance Ultraviolet Photodetectors Enabled by van der Waals Schottky Junction Based on TiO2 Nanorod Arrays/Au‐Modulated Ti3C2Tx MXene

“…[ 33 ] The expansion of the d ‐spacing from 9.26 to 13.93 Å compared to Ti 3 AlC 2 further confirms the complete exfoliation of few‐layered Ti 3 C 2 T x with the presence of surface terminations and water molecules between the MXene layers. [ 34 ] The diffraction peaks (101) and (002) are in good agreement with the tetragonal rutile phase (JCPDS no. 03‐065‐1119, a = 4.5933 Å and c = 2.9592 Å) of TiO 2 .…”

“…[ 33 ] Ti 2p core levels are fitted to five doublets (Ti 2p 3/2 , Ti 2p 1/2 ) located at Ti‐C (454.81, 460.3 eV), Ti 2+ (455.64, 461.11 eV), Ti 3+ (456.82, 461.96 eV), TiO 2 (458.21, 462.92 eV), and C‐Ti‐F x (459.21, 464.4 eV) bonds respectively, which are in agreement with the previously reported XPS results of MXenes with ‐F functional groups. [ 34 ] The Ti 3 C 2 T x MXene nanosheets on glass remain over 90% transmittance ranging from 300 to 850 nm (Figure 1e). The TiO 2 NRs exhibit high absorption in the UV‐A band (Figure 1f).…”

Recent Progress of Flexible Photodetectors Based on Low‐Dimensional II–VI Semiconductors and Their Application in Wearable Electronics

“…[ 60 ] Most recently, Kim and co‐workers developed a flexible capacitive photodetector with monolayer 2D MXene as transparent electrodes and the Cu‐doped ZnS semiconductor particles as photoactive materials. [ 56 ] The device exhibited excellent mechanical stability due to the high affinity between the MXene and flexible substrate.…”

Two-Dimensional Alloyed Mo0.5W0.5S2 Nanosheets for Photoelectrochemical Photodetection

“…M and X represent transition metal and chalcogen atom, respectively. Since the chalcogen atoms are saturated and the molecular interlayer force of the TMD material is weak, few-layer TMD can be obtained by mechanical exfoliation, vapor deposition methods, etc. − Due to the interlayer isolation of TMDs, 2D TMDs exhibit better properties than 3D TMDs, facilitating their potential advantages in electronics, photonics, biomedicine, and sensor. − For instance, Avdizhiyan et al created photodetectors (PDs) based on two-dimensional TMD alloys and showed that the spectral sensitivity of the created PDs can be significantly altered by changing the composition of TMD . Zhang et al have demonstrated that monolayer TMD nanosheets (NSs), including MoS 2 , TiS 2 , and TaS 2 , can serve as a sensing platform for DNA fluorescence detection, and they have been successfully used for multiplex detection of DNA …”