Highly sensitive broadband photomultiplication type all-polymer photodetectors and their applications in optical pulse counting

Broadband photomultiplication type all-polymer photodetectors (PM-APDs) are achieved on the basis of ITO/PFN-Br/PBDB-T : PYF-T-o (3 : 100, wt/wt)/LiF/Au as the configuration. Isolated hole traps are formed with PBDB-T encircled by PYF-T-o in the active layers. Trapped-holes in the vicinity of the Au electrode can cause interfacial band-bending to assist electron tunneling-injection into the active layers for achieving the PM phenomenon. The PM-APDs exhibit broad spectral response covering 310-900 nm, which is primarily dependent on the trapped-hole distribution in the vicinity of the Au electrode. The performance of PM-APDs could be improved by decreasing the active layer thickness, benefitting from the optimized electron tunneling-injection and collection. An ultrathin (similar to 1 nm) LiF layer is utilized as an interfacial layer to decrease electron injection barrier, leading to over one magnitude improvement of external-quantum-efficiency (EQE). The EQE of PM-APDs with the LiF layer could be increased to 18 000% at 360 nm and 9000% at 850 nm under 4 V applied bias, accompanied by the specific detectivity of 3.6 x 10(12) Jones at 360 nm and 4.2 x 10(12) Jones at 850 nm. The PM-APDs with the LiF layer are successfully applied in an optical pulse counting circuit, demonstrating the sensitive photodetection capability and feasibility in this practical application.