Engineering the optoelectronic properties of MoS₂ photodetectors through reversible noncovalent functionalization

Abstract

We present an easy drop-casting based functionalization of MoS2-based photodetectors that results in an enhancement of the photoresponse of about four orders of magnitude, reaching responsivities up to 100 A·W -1 . The functionalization is technologically trivial, air-stable, fully reversible and reproducible, and opens the door to the combination of 2D-materials with molecular dyes for the development of high performance photodetectors.Among the novel two-dimensional (2D) materials, 1-8 transition metal dichalcogenides (TMDCs) [9][10][11][12] show particularly promising electronic and optoelectronic properties. 13 In particular, their intrinsic bandgap within the visible part of the spectrum, makes them highly interesting materials for optoelectronic applications.14 In fact, the presence of a bandgap has allowed for the construction of a wealth of prototype electronic devices based on TMDCs. [15][16][17][18][19][20][21][22][23][24] In the last years, there has been a significant effort to modulate the optical properties of TMDCs in order to optimize the performance of the corresponding devices. Most of the strategies investigated so far rely on physical methods, such as strain-engineering, 25,26 fieldeffect doping, 12,27 or artificial stacking of different 2D materials. 28,29 In comparison, the chemical modification of TMDCs is still rather underexplored, despite the appealing combination of low-cost and high degree of control offered by synthetic chemistry. Examples of doping of TMDCs through surface charge-transfer using metal atoms, 30 gases, 31 and a few organic molecules has already been demonstrated. 32,33 Responsivities of just a few A·W -1 have been reported for MoS2 photodetectors functionalized with a rhodamine dye, 34 a rather modest value for MoS2-based photodetectors. Among the readily available organic dyes, perylenediimides (PDIs) and porphyrins show remarkable optical properties, including large molar absorptivity -ca. 10 5 M −1 cm −1 for PDIs and 10 6 M −1 cm −1 for porphyrins-, and outstanding photostability under ambient conditions. These intrinsic properties have made them two of the most popular families of organic dyes, particularly in the frame of photovoltaics. [35][36][37][38][39][40][41][42][43][44] However, their use for the modulation of the optoelectronic properties of TMDC-based devices has not been yet described. Considering this, we decided to investigate the effects of the noncovalent functionalization of MoS2 This is the post-peer reviewed version of the following article: A.J. Molina-Mendoza et al. "Engineering the optoelectronic properties of MoS2 photodetectors through reversible noncovalent functionalization" Chem. Comm., 2016 DOI: 10.1039/C6CC07678E Which has been published in final form at: http://pubs.rsc.org/en/content/articlelanding/2016/cc/c6cc07678e#!divAbstract photodetectors with the soluble PDI and tetraphenyl porphyrin (TPP) depicted in Chart 1. Here, we describe that the supramolecular functionalization of mechanically exfoliated MoS2-based photodetector...

Molecular Functionalization of Two‐Dimensional MoS2 Nanosheets

“…[40] The photogenerated chargesw ere trapped into localizeds tates within the band gap of MoS 2 and found to quencht he exciton recombination, hence resulting to photoconductivity increment, photogating effect.I na ddition, the widely used organic dye Rhodamine 6G was found to enhance the photogenerated current by an order of magnitude in devices in which the dye was spin-coated onto mechanicallye xfoliated MoS 2 monolayers. The organic dyes can be easily drop-casted onto MoS 2 nanosheets and stabilizedb yw eak electrostatic forces in ar eversible non-destructive manner.T hese electron-donating dyes increaset he ndoping of mechanicallye xfoliated nanosheets and enhance the photocurrentb yf our orders of magnitude at ambient conditions.…”

“…The organic dyes can be easily drop-casted onto MoS 2 nanosheets and stabilizedb yw eak electrostatic forces in ar eversible non-destructive manner.T hese electron-donating dyes increaset he ndoping of mechanicallye xfoliated nanosheets and enhance the photocurrentb yf our orders of magnitude at ambient conditions. [40] The photogenerated chargesw ere trapped into localizeds tates within the band gap of MoS 2 and found to quencht he exciton recombination, hence resulting to photoconductivity increment, photogating effect.I na ddition, the widely used organic dye Rhodamine 6G was found to enhance the photogenerated current by an order of magnitude in devices in which the dye was spin-coated onto mechanicallye xfoliated MoS 2 monolayers. Electronsw ere transferred from the photoexcited sensitizer to MoS 2 and the hybrids found to be photoresponsive in ab road spectralr ange from 405 to 980 nm, demonstrating the occurrenceo fp hotoinduced charge-transfer phenomena at the interface.…”

Controlled Covalent Functionalization of 2 H‐MoS2 with Molecular or Polymeric Adlayers

“…Decoration of TMDCs with molecular fragments via noncovalent approaches, mostly based on dispersion/solvophobic interactions, is relatively easy and has consequently led the way towards potential applications. For example, selective chemical sensors and enhanced photodetectors have already been described using this strategy. Methods for the covalent modification of TMDCs are much scarcer and nearly exclusively limited to the metallic 1T phase …”

Recent Progress and Future Prospects of 2D‐Based Photodetectors

“…It is noted that carbon nanotubes were also combined with graphene to form hybrid photodetectors with broadband spectral response (covering 400–1550 nm), a high responsivity of 4100 A W −1 , and a fast response time of 100 µs . Besides graphene, 2D TMDs such as MoS 2 and WS 2 have also been combined with organic materials to achieve hybrid photodetectors . For instance, Yu et al reported dye‐sensitized MoS 2 photodetectors utilizing a single‐layer MoS 2 treated with rhodamine 6G organic dye molecules.…”