Highly Efficient Rubrene–Graphene Charge-Transfer Interfaces as Phototransistors in the Visible Regime

Abstract

Atomically thin materials such as graphene are uniquely responsive to charge transfer from adjacent materials, making them ideal charge-transport layers in phototransistor devices. Effective implementation of organic semiconductors as a photoactive layer would open up a multitude of applications in biomimetic circuitry and ultra-broadband imaging but polycrystalline and amorphous thin films have shown inferior performance compared to inorganic semiconductors. Here, the long-range order in rubrene single crystals is utilized to engineer organic-semiconductor–graphene phototransistors surpassing previously reported photogating efficiencies by one order of magnitude. Phototransistors based upon these interfaces are spectrally selective to visible wavelengths and, through photoconductive gain mechanisms, achieve responsivity as large as 10⁷ A W⁻¹ and a detectivity of 9 × 10¹¹ Jones at room temperature. These findings point toward implementing low-cost, flexible materials for amplified imaging at ultralow light levels.

Responsivity, detectivity, and photogating quantum efficiency as high as 10⁷ A W⁻¹, 9 × 10¹¹ Jones, and 1% are achieved in an entirely organic graphene-based phototransistor by employing a rubrene single crystal as the photoactive layer. Long-range diffusion of triplet excitons in rubrene overcomes conflicting requirements for efficient light absorption and charge extraction, pointing toward amplified imaging of ultraweak light signals in biocompatible sensors.

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