n-Type polythiophene as a hole-blocking layer in inverted organic photodetectors

Organic photodetectors (OPDs) own unique advantages such as light weight, flexibility, low production cost, tunable detection wavelength, and thus are promising for a variety of applications. The lack of hole-blocking layer (HBL) materials impedes the reduction of dark current density and the enhancement of the performance of OPDs. Herein, we employed an n-type polythiophene n-PT1 as a HBL material for inverted OPDs. The specific solubility of n-PT1 in o-dichlorobenzene facilitates solution processing and enables multilayer device fabrication. The ultradeep-lying highest occupied molecular orbital energy level ensures a large hole injection barrier between cathode and active layer that suppresses dark current. As a result, compared to the control devices without n-PT1, the inverted OPD devices with n-PT1 as HBL demonstrate a two-order-of-magnitude reduction in dark current density and a one-order-of-magnitude increase in specific detectivity. To the best of our knowledge, this is the first solution processable HBL material for inverted OPDs.