Modulating Persistent Photoconductivity through Barrier Engineering for High-performance and Multifunctional Two-dimensional Optoelectronic Devices.

2D optoelectronic devices, such as photomemory and photodetectors, have exceptional potential for realising multifunctional applications. Modulating persistent photoconductivity (PPC) is key to enabling diverse functionalities and optimising device performance. However, PPC in 2D devices is difficult to modulate due to surface defects (trap states), Fermi level pinning, and the Schottky barrier height at junctions. In this study, we demonstrate that reducing surface defects and Fermi level pinning enables barrier engineering for effective PPC modulation. The persistent photoconductivity gain (PPCG) is tunable from 307.6% to 4.72%, enabled by tailoring the Schottky barrier height through a van der Waals contact strategy. A high PPCG (307.6%) is achieved in a high-barrier Au/MoS2 junction, suitable for optoelectronic synapses, neuromorphic computing, and photomemory applications, with a relaxation current linearity of up to 0.986. A low PPCG (4.72%) is achieved in a low-barrier 1T'-WTe2/MoS2 junction, designed for photodetectors with an on/off ratio of 105, a response time of 2 ms, and a responsivity of 30.1 A/W. These findings advance the understanding of PPC and provide new avenues for designing high-performance 2D optoelectronic devices.