Employing liquid crystal material as regulator to enhance performance of photomultiplication type polymer photodetectors

Abstract

Photomultiplication type polymer photodetectors (PM-PPDs) were achieved with PBDB-T:BTPV-4F (98:2, wt/wt) as blend active layer based on a sandwich structure. Isolated electron traps are formed due to the rather less BTPV-4F surrounded by PBDB-T in blend active layers. Trapped electrons in BTPV-4F near Al electrode will induce interfacial band bending for hole tunneling injection into blend active layers. The tunneling injected holes will be transported along the channels formed by PBDB-T in blend active layers, photomultiplication phenomenon will be obtained when the number of holes crossing through blend active layers is larger than that of incident photons per unit time. Liquid crystal material BTR was selected as regulator to adjust PBDB-T molecular arrangement for improving hole mobility in blend active layers, leading to optimized performance of PM-PPDs. Optimal PM-PPDs were obtained with PBDB-T:BTR:BTPV-4F (89:9:2, wt/wt/wt) as blend active layer. The external quantum efficiency (EQE) values of optimal PM-PPDs are 1.5 times that of PM-PPDs based on PBDB-T:BTPV-4F (98:2, wt/wt) in the whole spectral response range under −10 V applied bias. The EQE of optimal PM-PPDs can be markedly improved by increasing applied bias, which is improved from 600% to 19,300% at 660 nm with applied bias increased from −10 to −20 V. The responsivity of optimal PM-PPDs arrives to 102 A W−1 at 660 nm under −20 V applied bias.