Multi-layered MoS2 phototransistors as high performance photovoltaic cells and self-powered photodetectors

An optoelectronic diode based on a p–n junction is one of the most fundamental device building blocks with extensive applications. Compared with graphene, layered transition-metal dichalcogenides demonstrate promising applications in novel valley-electronics and opto-electronics. Here we reported the fabrication and optoelectronic properties of a single multilayer MoS2 sheet. Our results indicate that the thin MoS2 shows a linear transport property while thick MoS2 shows diode characteristics with well-defined current rectification behavior. We assign that the rectification behavior is due to the formation of a p–n junction in the single multilayer MoS2 piece. The intrinsic defects in MoS2 can change the conduction polarity, such as: sulfur vacancies contribute to the n-type behavior while sulfur interstitials and molybdenum vacancies contribute to the p-type conduction. The variation of intrinsic defects and stoichiometry is obvious over the micrometer range in thick MoS2. The fabricated MoS2 transistors were assessed under bias and gate voltage modulation when exposed to red, green and UV light under vacuum. The multilayer MoS2 shows dominant p-type behavior under dark conditions while its shows dominant n-type conduction under light illumination. In addition, this MoS2 phototransistor shows an evident photovoltaic effect. The open-circuit voltage (Voc) and short-circuit current (Isc) are observed to be −0.48 V and 494 nA under red illumination. These results demonstrate the potential application of a single multilayer MoS2 sheet in optoelectronics, such as light-emitting diodes (LEDs), field-effect photovoltaic cells and photodetectors.