Poly(4-styrenesulfonate)-induced sulfur vacancy self-healing strategy for monolayer MoS2 homojunction photodiode

Abstract

We establish a powerful poly(4-styrenesulfonate) (PSS)-treated strategy for sulfur vacancy healing in monolayer MoS2 to precisely and steadily tune its electronic state. The self-healing mechanism, in which the sulfur vacancies are healed spontaneously by the sulfur adatom clusters on the MoS2 surface through a PSS-induced hydrogenation process, is proposed and demonstrated systematically. The electron concentration of the self-healed MoS2 dramatically decreased by 643 times, leading to a work function enhancement of ∼150 meV. This strategy is employed to fabricate a high performance lateral monolayer MoS2 homojunction which presents a perfect rectifying behaviour, excellent photoresponsivity of ∼308 mA W−1 and outstanding air-stability after two months. Unlike previous chemical doping, the lattice defect-induced local fields are eliminated during the process of the sulfur vacancy self-healing to largely improve the homojunction performance. Our findings demonstrate a promising and facile strategy in 2D material electronic state modulation for the development of next-generation electronics and optoelectronics.

Atomic Vacancy Control and Elemental Substitution in a Monolayer Molybdenum Disulfide for High Performance Optoelectronic Device Arrays

“…In parallel, ultraviolet photoelectron spectroscopy (UPS) measurements were performed on the pristine, UV‐N 2 , and UV‐N 2 /O 2 MoS 2 films (Figure c) and the corresponding work functions (Φ) are calculated using the relation Φ = hν – E onset , where hν is the incident photon energy (21.2 eV) and E onset is the cut‐off edge of the secondary electrons. The extracted work function of the pristine MoS 2 monolayer is 4.40 eV, which well matches to the metrics reported in the previous reports . The extracted work functions of the UV‐N 2 and UV‐N 2 /O 2 MoS 2 are 4.30 and 4.52 eV, respectively (Figure b).…”

“…Furthermore, the valence band edges ( E V ) of the UV‐N 2 and UV‐N 2 /O 2 MoS 2 extracted by linearly extrapolating the leading edge of UPS data to the base line exhibit the blue‐ (+0.08 eV) and red‐shift (−0.1 eV), respectively, with respect to the pristine MoS 2 . This implies that the sulfur vacancy formation in the UV‐N 2 MoS 2 leads to shifting the Fermi level closer to the conduction band edge (i.e., n‐doping), whereas oxygen substitution in the UV‐N 2 /O 2 MoS 2 leads to shifting the Fermi level closer to the valence band edge (i.e., p‐doping) . Moreover, work functions of UV‐treated MoS 2 are efficiently modulated by the duration of UV exposure time (Figure S6, Supporting Information), revealing that the photon‐assisted defect engineering is an effective route to delicately modulate the doping density in a MoS 2 monolayer.…”

Si/CuIn0.7Ga0.3Se2 Core–Shell Heterojunction for Sensitive and Self‐Driven UV–vis–NIR Broadband Photodetector

“…The secondary‐electron cutoff binding energy ( E cutoff ), acquired from the tangent on the left side of the full spectrum (Figure S2b, Supporting Information), is 16.25 eV. The work function ( f ) of CIGS is calculated to be 4.97 eV according to the equationwhere hν is the incident photon energy of 21.22 eV. Then, by linearly extrapolating the onset part of the UPS spectrum (Figure S2c, Supporting Information), the difference between the Fermi level ( E F ) and E V is calculated to be 0.25 eV.…”

Two‐dimensional heterostructure promoted infrared photodetection devices

“…Homojunction is a special homo‐heterostructure constructed by same semiconductor with different crystal faces, semiconducting types, and exposing faces, etc. 2D homojunction delivers identical crystal structure and continuous band alignments in the interface, leads to ideal current rectifying behavior and high efficient photoresponse, which shows better performance than heterostructure . Thus, homo‐heterostructures based on thin‐layer TMDs have attracted much research interest .…”

“…2D homojunction delivers identical crystal structure and continuous band alignments in the interface, leads to ideal current rectifying behavior and high efficient photoresponse, which shows better performance than heterostructure. 97,98 Thus, homo-heterostructures based on thin-layer TMDs have attracted much research interest. 99 Huo et al 57 employed the MoS 2 P-N homojunction for an ultrasensitive photodetector.…”