Effect of a pi-linker of push-pull D-pi-A donor molecules on the performance of organic photodetectors

摘要

We report organic photodetectors (OPDs) exhibiting high photocurrent density (J(ph)), low dark current density (J(d)), and broadband external quantum efficiency (EQE) based on three push-pull type D-pi-A small molecule donors (H1,H2, andH3) with different pi-linker structures. Among the three donor molecules,H2with a long pi-linker had stronger intermolecular interactions and formed a polycrystalline structure, thus generating subgap states and trap sites at the interface, which increased theJ(d)value of OPDs because of the facilitated electron injection from the indium tin oxide electrode to the donor at reverse bias and decreased theJ(ph)value. In contrast,H3with a short pi-linker showed amorphous morphology in thin films because of weaker intermolecular interactions, lowering theJ(d)value in both planar heterojunction (PHJ) OPDs and bulk heterojunction (BHJ) OPDs. The BHJ OPDs withH3exhibited a broadband EQE value of 64% at 530 nm, a lowJ(d)value of 1.8 x 10(-8), and a highJ(ph)value of 9.6 x 10(-3)A cm(-2)at -3 V bias.