Tunable Photoelectric Properties of n-Type Semiconducting Polymer:Small Molecule Blends for Red Light Sensing Phototransistors

Semiconducting blend heterostructures, composed of conjugated polymer with photoresponsive organic crystals, provide an effective way to achieve promising photodetection devices. Here, solution-processed n-type N2200 conjugated polymer and quinoidal thienoisoindigo (TIIQ) small molecule blend is used to construct phototransistors for red light detection. The device performance of the optically switchable phototransistors can be tuned by the relative composition in the blend. The key feature is red light (680 nm) illuminated intensity-tunable photodetection enabling the highest photoresponsivity (R) of 4065 A W^-1 and specific photodetectivity (D^*) of 1.4 × 10¹³ Jones for an 88% blend device. At the same time, maintaining high mobility (μ) of 1.59 cm² V^-1 s^-1, since the efficient extraction of photogenerated charges from blend heterointerface, benefiting from blending with higher μ and enhanced absorption of TIIQ, contributes to improvement in the red light photoresponse of the N2200:TIIQ blend phototransistor. This work demonstrates that the semiconducting blend strategies provide opportunities for developing high performance organic phototransistors.