Few‐Layer Organic Crystalline van der Waals Heterojunctions for Ultrafast UV Phototransistors

Abstract

Organic UV photodetectors using a transistor architecture can yield higher photoresponsivity than diode‐based devices because of the presence of a gate electrode. However, a long‐term issue of these phototransistor devices is the slow response speed, which hinders their practical applications. Here, organic UV phototransistors are constructed using few‐layer organic crystalline van der Waals (vdW) heterojunctions as the photoactive layers. The thickness of the photoactive layers is even less than the exciton diffusion length, thus removing the exciton‐diffusion bottleneck and giving rise to the confinement of charge separation and recombination within the adjacent molecular layers across the heterojunction interface. Hence, the phototransistor devices can exhibit a remarkably enhanced response speed (rise and decay times as short as only ≈4 and 6 ms, respectively). The layer‐dependent photoresponse characteristics are also observed, reinforcing the great importance of few‐layer organic heterostructures in phototransistor devices. This work not only provides a promising avenue toward fast response optoelectronic devices but also presents an in‐depth understanding on the microscopic nature of photogenerated charge carriers at the precision of molecular layers.

Retina‐Inspired Self‐Powered Artificial Optoelectronic Synapses with Selective Detection in Organic Asymmetric Heterojunctions

“…Thus, this indicates the formation of C 8 ‐BTBT/F 16 CuPc heterojunctions. [ 27 ] We further characterized the morphologic properties of the heterojunctions via atomic force microscopy (AFM) (Figure 1d,e and Figure S1d (Supporting Information)). The results showed that the thicknesses of the C 8 ‐BTBT, PMMA, and F 16 CuPc films are ≈5.7, 6.0, and 10.2 nm, respectively.…”

Evolutionary 2D organic crystals for optoelectronic transistors and neuromorphic computing

“…2D OSs with well-defined interfaces and precisely adjusted thicknesses have various of potential for physical implementation of phototransistors because their tunable energy gap can cover a large spectrum range from near-infrared to ultraviolet [53,54,[130][131][132][133]. Low photogating efficiency, low carrier mobility, and short photo-induced exciton diffusion distance in bulk organic materials, on the other hand, impede the development of highly efficient and fast response phototransistors [134][135][136][137]. In order to ensure photo-generated exciton separation, the thickness of the photoactive layer should be lowered below 10 nm [138].…”

“…Furthermore, the interlayer screening effect found in thick photoactive materials impedes photocurrent decay characteristics. Guo et al built a few-lay N,N -(1-hexyl)-1,4,5,8-naphthalenetetracarboxydiamide (NDI-C 6 )/C 8 -BTBT van der Waals heterojunction to overcome the exciton-diffusion bottleneck and restrict exciton separation/recombination in the year 2020 [134] (Inset of figure 10(a)). As presented in figure 10(a), the authors extracted the photoresponsivity and sensitivity to evaluate the device's performance, which are 1.78 A/W and 50, respectively.…”

Patterning 2D Organic Crystalline Semiconductors via Thermally Induced Self‐Assembly

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] To date, 2DOCS-based field-effect transistors (FETs) have experienced impressive mobility enhancement; [17][18][19] the charge-carrier-transport and injection physics have also been explicitly elucidated. [20][21][22] These fascinating breakthroughs have thus greatly motivated performance optimization of tremendous organic functional devices, including transistor memories, [23,24] photodetectors, [25,26] light-emitting diodes, [27] and biosensors. [28,29] To further expand the practical application of available 2DOCSs to cost-effective, high-throughput manufacturing functional devices and integrated circuits, patterning of 2DOCSs, which has never been experimentally demonstrated, is undoubtedly an essential prerequisite.…”