Dirac Point Modulated Self-Powered Ultrasensitive Photoresponse and Color-Tunable Electroluminescence from Flexible Graphene/Metal–Organic Frameworks/Graphene Vertical Phototransistor

Abstract

Integrated wearable optoelectronic devices synchronously exhibit contradictory phenomena of exciton generation and recombination with their control by an external electric field, and the mechanical strain associated with this has widespread applications. However, a demonstration of such single-miniaturized multifunctional wearable optoelectronics remains a daunting challenge. A versatile metal–organic framework (MOF) possesses tailorable outstanding optical properties through an inherent multiple charge-transfer mechanism between metal and ligand. Yet, its commercialization remains unsuccessful because of large porosity, poor conductivity, and deficient crystallinity. Graphene is honorable for its outstanding optoelectronic and mechanical behaviors. Combining excellent features of a versatile MOF with monolayer graphene, unprecedently, we report a self-powered ultrasensitive (external quantum efficiency ∼3 × 1010%) and ultrafast (response time ≈ 220 μs) wearable vertical phototransistor by utilizing a graphene/MOF/graphene/poly(vinylidene fluoride-co-trifluoroethylene) heterojunction on a flexible polydimethylsiloxane substrate through the formation of asymmetric Schottky junctions at MOF/graphene interfaces by a judicious incorporation of a piezo-sensitive poly(vinylidene fluoride) layer. Importantly, by the Dirac point modulation of graphene through a mechanical strain, we achieve optical strain sensors that can modify the amplitude and polarity of the photocurrent. Additionally, controlling the Dirac point of graphene and charge-transfer mechanisms of the MOF by a suitable electrical bias and strain, we demonstrate color-tunable broadband light emission from a flexible vertical phototransistor. Our unique discovery will enrich wearable integrated optoelectronics.