High-Performance\nAll-Polymer Photodetectors Enabled\nby New Random Terpolymer Acceptor with Fine-Tuned Molecular Weight

Abstract

Reducing the dark current density\nand enhancing the overall performance\nof the device is the focal point in research for organic photodetectors.\nTwo novel random terpolymers (P3 and P4) with different molecular\nweights are synthesized and evaluated as acceptors in bulk heterojunction\n(BHJ) polymer photodetectors. Compared with known acceptor materials,\nsuch as N2200 (P1) and F-N2200 (P2), polymer P4 has a lower lowest\nunoccupied molecular orbital (LUMO) energy level, favorable morphology,\nand good miscibility with a donor material J71, which leads to proper\nphase separation of the blend film and better dissociation of excitons\nand transport of carriers. Therefore, a considerably low dark current\ndensity (<i>J</i>_d) of 1.9 × 10^–10 A/cm² and a high specific detectivity (<i>D</i>*) of 1.8 × 10¹³ cm Hz^1/2/W (also “Jones”)\nat 580 nm under a −0.1 V bias are realized for the P4-based\nphotodetector. More importantly, the device also exhibits a fast response\nspeed (τ_r/τ_f = 1.24/1.87 μs)\nand a wide linear dynamic range (LDR) of 109.2 dB. This work demonstrates\nthat high-performance all-polymer photodetectors with ideal morphology\ncan be realized by random polymer acceptors with a fine-tuned molecular\nweight.