Advances in solution-processable near-infrared phototransistors

Solution processable near infrared (NIR) photodetectors provide a promising alternative due to their low cost, flexible design, adaptability to various fabrications, and large area manufacturability, removing the limitations of traditional wafer-based inorganic semiconductor techniques. There are three typical solution-processable NIR photodetectors: photodiodes (PDs), photoconductors (PCs) and phototransistors (PTs). PDs have a stack of functional layers sandwiched between an anode and a cathode. The external quantum efficiency (EQE) of the NIR PDs and PCs cannot be higher than 100%. In comparison, NIR PTs are three-terminal devices with an ultra-low noise current, providing high sensitivity and tunable gain with an EQE in excess of 100%, achieved by controlling unbalanced charge transport through an optically controlled gate terminal. This review provides a brief introduction with regard to the device configuration and operation mechanism of PTs, followed by a comprehensive overview of the recent advances in solution processable NIR PTs. This includes different approaches for attaining high-sensitivity NIR PTs using single component, heterojunction and nano-structured channel layers. The advances in solution-processable NIR PTs with novel device design knowledge and new materials processing technologies are highlighted. High sensitivity NIR photodetectors for applications in visualizing NIR light, and health and safety monitoring are also discussed.