Semifluoroalkyl n‐Type Conjugated Polymers: Novel Cathode Interlayers for Air‐Stable Organic Photodetectors

Abstract Typical organic cathode interlayer (CIL) materials for solution‐processed organic optoelectronic devices usually have polar side chains or polar/ionic groups, making them hydrophilic and thus limiting device stability. This manuscript reports a novel CIL material based on an n‐type polythiophene backbone with semifluoroalkyl side chains (n‐PT11) for developing high‐performance organic photodetectors (OPDs) with excellent device stability. The n‐type polythiophene backbone of n‐PT11 has a low‐lying LUMO/HOMO energy level of −4.27 eV/−6.21 eV, suppressing reversed hole injection. The semifluoroalkyl side chains enable n‐PT11 processing with 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) for fabricating multilayer OPDs and exhibit low trap density for suppressing dark current density ( J d ). As a result, n‐PT11‐based near‐infrared (NIR) OPDs exhibit an ultra‐low J d of 1.00 × 10 −9 A cm −2 and a high specific detectivity ( D * ) of 3.06 × 10 12 cm Hz 1/2 W −1 at −1 V, which is among the highest D * values reported so far for NIR OPDs. Most importantly, the hydrophobicity of n‐PT11 allows the OPD unprecedented air stability, with unencapsulated OPDs retaining 94% of their initial responsiveness after 2000 h in ambient conditions. To the best knowledge, this is the first report of conjugated polymers with semifluoroalkyl side chains as CILs in OPDs.