Charge-Transfer Effect and Enhanced Photoresponsivity of WS₂- and MoSe₂-Based Field Effect Transistors with π-Conjugated Polyelectrolyte

Abstract

The characteristics of field effect transistors (FETs) fabricated using two-dimensional (2D) transition-metal dichalcogenides (TMDCs) can be modulated by surface treatment of the active layers. In this study, an ionic π-conjugated polyelectrolyte, poly­(9,9-bis­(4′-sulfonatobutyl)­fluorene-alt-1,4-phenylene) potassium (FPS-K), was used for the surface treatment of MoSe2 and WS2 FETs. The photoluminescence (PL) intensities of monolayer (1L)-MoSe2 and 1L-WS2 clearly decreased, and the PL peaks were red-shifted after FPS-K treatment, suggesting a charge-transfer effect. In addition, the n-channel current of both the MoSe2 and WS2 FETs increased and the threshold voltage (V th) shifted negatively after FPS-K treatment owing to the charge-transfer effect. The photoresponsivity of the MoSe2 FET under light irradiation (λex = 455 nm) increased considerably, from 5300 A W–1 to approximately 10 000 A W–1, after FPS-K treatment, and similar behavior was observed in the WS2 FET. The results can be explained in terms of the increase in electron concentration due to photogating. The external quantum efficiency and photodetectivity of both FETs were also enhanced by the charge-transfer effect resulting from surface treatment with FPS-K containing mobile cations (K+) and fixed anions (SO3 –), as well as by the photogating effect. The variation in charge-carrier density due to the photogating and charge-transfer effects is estimated to be approximately 2 × 1012 cm–2. The results suggest that π-conjugated polyelectrolytes such as FPS-K can be a promising candidate for the passivation of TMDC-based FETs and obtaining enhanced photoresponsivity.

Surface-Plasmonic-Coupled Photodetector Based on MAPbI3 Perovskites with Au Nanoparticles: Significantly Enhanced Photoluminescence and Photodetectivity

“…Time-resolved PL (tr-PL) spectra were measured using the LCM with a time-correlated single photon counting system (Simple-Tau) using a 488 nm laser for excitation at a power of 100 nW. The details of the methods of LCM measurement have been previously reported. , The photoresponsive electrical characteristics of the photodetectors were measured using high-voltage source measurement units (Keithley 2634B) under vacuum (≤60 mTorr) at room temperature. A collimated LED lamp (λ ex = 505, 633, and 735 nm) was used for light irradiation.…”

“…The details of the methods of LCM measurement have been previously reported. 43,44 The photoresponsive electrical characteristics of the photodetectors were measured using high-voltage source measurement units (Keithley 2634B) under vacuum (≤60 mTorr) at room temperature. A collimated LED lamp (λ ex = 505, 633, and 735 nm) was used for light irradiation.…”

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

“…Graphene (Gr), being the most heavily investigated one, has a 2D lattice composed of sp 2 -hybridized carbons and all six-membered rings (i.e., the honeycomb structure, Figure a). , On one hand, π-bonds induced by sp 2 hybridization promote in-plane charge transport in graphene. , On the other hand, the honeycomb structure gives rise to a centrosymmetric Brillouin zone with zero-band gap points between valence and conduction bands (termed “charge neutrality point (CNP)”, also called as “Dirac point”). − In single-layer graphene, the in-plane directions can be defined as “armchair” and “zigzag”. , The armchair/zigzag edge provides graphene with distinct properties including the mobility and coupling effect, which adds functionalities of graphene-based electronics. , The armchair/zigzag edges also increase the difficulty to precisely control the functionalization density on graphene, because the crystalline basal planes are less reactive than the edges . Thus, the literature reports a vast number of methods to achieve a uniform and precise modification of graphene by using covalent bonds or noncovalent intermolecular forces, such as π–π stacking forces, n-hydroxysuccinimide/carbodiimide hydrochloride chemistry, laser-assisted technology, and others.…”

“…128,129 The armchair/zigzag edges also increase the difficulty to precisely control the functionalization density on graphene, because the crystalline basal planes are less reactive than the edges. 130 Thus, the literature reports a vast number of methods to achieve a uniform and precise modification of graphene by using covalent bonds or noncovalent intermolecular forces, such as π−π stacking forces, 131 n-hydroxysuccinimide/carbodiimide hydrochloride chemistry, 97 laser-assisted technology, 132 and others. TMDs are layered materials that consist of two major types: semiconducting TMDs and metallic TMDs.…”

Organic photodetectors with high detectivity for broadband detection covering UV-vis-NIR

“…Thus, the real specific detectivity should be obtained from an accurate assessment of the dark current noise of the devices. [48][49][50] Therefore, we further measured the total noise current of the devices under À0.1 V as shown in Fig. 2c.…”