Delayed Charge Recombination by Open‐Shell Organics: Its Application in Achieving Superb Photodetectors with Broadband (400–1160 nm) Ultrahigh Sensitivity and Stability

Abstract

in this area following the emergence of atomically thin 2D materials, such as graphene, MoS 2 and other types of transition-metal dichalcogenides (TMDs), have offered promising routes to enhance functionality in photodetection. [2][3][4][5][6][7][8][9][10][11] This functionality mainly lies in their unique electronic and optical properties arising from the monolayer van der Waals heterostructure. [2][3][4][5][6][7][8][9][10][11] Among the various 2D materials that have been employed in ultrathin optoelectronic devices, MoS 2 has been highlighted because of extremely high stability, a direct bandgap, [9,12] reliable scalable synthesis, [10] excellent optoelectronic performances [9,12] and capability for heterogeneous integration. [13][14][15] For example, MoS 2 -based PDs derived from single-and/or multilayer MoS 2 have been reported to respond to ultraviolet (UV) and visible light illumination, rendering photo responsivities up to 880 A W −1 (monolayer) 7 and ≈0.6 A W −1 (few layers), [12] despite a relatively small bandgap (1.2 eV for MoS 2 ). However, the insufficient photoactive region in the atomically thin layer (≈0.7 nm) [16,17] makes it necessary to incorporate photoactive materials with TMDs for complementary absorption, which has been demonstrated to be a promising way to achieve better Monolayer transition-metal dichalcogenides have inspired worldwide efforts in optoelectronic devices but real applications are hindered with their reduced optical absorption due to their atomically ultrathin signature. In this study, by utilizing their biradical nature such as excellent absorption coefficient, broad bandwidth from the ultraviolet to near-infrared region, and small tripletsinglet energy gap, a series of helicene 5,14-diaryldiindeno[2,1-f:1′,2′-j]picene (DDP) derivatives (1ab, 1ac, and 1bb) are integrated with monolayer MoS 2 for extraordinary photodetector performance and outstanding stability. Via comprehensive time-resolved studies, the interfacial charge-transfer process from the DDPs to the MoS 2 layer is evidenced by the stabilized exciton property of the organics (1ac)/MoS 2 heterostructure. Significantly, the 1ac/MoS 2 photodetector exhibits an ultrahigh photoresponsivity of 5 × 10 7 A W −1 and a fast response speed of 45 ms due to the highly efficient photoexcited carrier separation and the matched type-II energy band alignment. The biradical 1ac/ MoS 2 hybrid photodetector shows no sign of degradation after one-month operation. The results pave a new avenue for biradical based high-performance and super-broadband optoelectronic devices.

A review of molybdenum disulfide (MoS2) based photodetectors: from ultra-broadband, self-powered to flexible devices

“…[311][312][313] The rise/fall times of photodetectors was found to decrease with increasing light intensity where the rise times varied from 54 wavelength. Shen et al 368 synthesized a series of helicene 5,14-diaryldiindeno[2,1-f:1 0 ,2 0 -j]picene (DDP) derivatives namely 5,14-dimesityldiindeno[2,1-f:1 0 ,2 0 -j]picene (1ab), 5,14bis(2,4,6-trimethoxyphenyl)diindeno[2,1-f:1 0 ,2 0 -j]picene (1ac), and 9,10-dimethyl-5,14-dimesityldiindeno[2,1-f:1 0 ,2 0 -j]picene (1bb) and integrated with monolayer MoS 2 to develop hybrid photodetectors. Time-resolved measurements showed the interfacial charge-transfer from the DDP derivative to the monolayer MoS 2 conrmed by the stability of exciton property of the (1ac)/MoS 2 organics/inorganic hybrid heterostructure.…”

Two-Dimensional Field-Effect Transistor Sensors: The Road toward Commercialization

“…(1) Responsivity . As a vital performance merit of photodetectors, responsivity ( R ph , also known as photoresponsivity) is defined as the ratio of the photoconductive gain and can be expressed by eq . , where I ph is the photocurrent ( I ph = I light – I dark ); P light is the incident laser density; A is the effective area; and I light and I dark refer to the current under light and dark, respectively.…”

“…As a vital performance merit of photodetectors, responsivity (R ph , also known as photoresponsivity) is defined as the ratio of the photoconductive gain and can be expressed by eq 11. 311,312 = R I P A /( )…”

Synthesis, Characterization, and Thin-Film Transistor Response of Benzo[i]pentahelicene-3,6-dione

“…Despite their peculiar properties, however, helicenes still remain rather unexplored in solid-state (opto-)electronic devices. Racemic mixtures of tetrathia-[7]-helicene [ 27 ], naphthalene double [6]helicenes [ 28 ], pyrene double [4]heterohelicene [ 29 ], 5,14-diaryldiindeno[2,1-f:1′,2′-j]picene [ 30 , 31 ], perylene diimide double-[5]heterohelicene [ 32 , 33 ], and a multiple helicene containing two [5]helicene and four [4]helicene moieties [ 34 ] have been used in organic thin-film transistors (OTFTs). Some authors exploited the chirality of the helicenes by using the enantiomerically pure 1-aza[6]helicene [ 35 ] and perylene diimide double-[7]heterohelicene [ 36 ] in circularly polarized detecting OTFTs.…”