Polymer: Non-fullerene acceptor heterojunction-based phototransistor for short-wave infrared photodetection

It remains full of challenge for extending short-wave infrared (SWIR) spectral response and weak-light detection in the context of broad spectral responses for phototransistor. In this work, a novel poly(2,5-bis(4-hexyldodecyl)-2,5-dihydro-3,6-di-2-thienyl-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-thiophene) (PDPPT3-HDO):COTIC-4F organic bulk-heterojunction is prepared as active layer for bulk heterojunction phototransistors. PDPPT3-HDO serves as a hole transport material, while COTIC-4F enhances the absorption of SWIR light to 1020 nm. As a result, smooth and connected PDPPT3-HDO film is fabricated by blade coating method and exhibits high hole mobility up to 2.34 cm²·V⁻¹·s⁻¹ with a current on/off ratio of 4.72 × 10⁵ in organic thin film transistors. PDPPT3-HDO:COTIC-4F heterojunction phototransistors exhibit high responsivity of 2680 A·W⁻¹ to 900 nm and 815 A·W⁻¹ to 1020 nm, with fast response time (rise time ~ 20 ms and fall time ~ 100 ms). The photosensitivity of the heterojunction phototransistor improves as the mass ratio of non-fullerene acceptors increases, resulting in an approximately two orders of magnitude enhancement compared to the bare polymer phototransistor. Importantly, the phototransistor exhibits decent responsivity even under ultra-weak light power of 43 μW·cm⁻² to 1020 nm. This work represents a highly effective and general strategy for fabricating efficient and sensitive SWIR light photodetectors.