Highly Photosensitive Vertical Phototransistors Based on a Poly(3-hexylthiophene) and PbS Quantum Dot Layered Heterojunction

We fabricated a vertical field effect phototransistor with Au/Ag nanowires as the transparent source electrode and with vertically stacked layers of poly(3-hexylthiophene) (120 nm) and lead sulfide quantum dots (380 nm), which formed heterojunctions. The built-in electric field in the layered heterojunction aids the separation of photoinduced excitons, while the short channel enables efficient carrier transport across the active region. Both of these benefits enable a high photoperformance and fast photoresponse. This vertical phototransistor can be operated at room temperature with a low operation voltage of −1 V and is therefore energy-efficient. Further, it has a wide response spectrum from 400 to 2100 nm, a high photoresponsivity of more than 9 × 104 AW–1, and a high detectivity of up to 2 × 1013 Jones (cm Hz1/2 W–1) under infrared illumination. Additionally, this vertical phototransistor had a response time of 9 ms, which is faster than a previously reported lateral field effect phototransistor based on poly(3-hexylthiophene)/lead sulfide quantum dots. The vertical architecture combined with the layered heterojunction approach provides a new, facile way of fabricating high performance devices.