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

Abstract

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–π–A small molecule donors (H1, H2, and H3) with different π-linker structures. Among the three donor molecules, H2 with a long π-linker had stronger intermolecular interactions and formed a polycrystalline structure, thus generating subgap states and trap sites at the interface, which increased the J_d value of OPDs because of the facilitated electron injection from the indium tin oxide electrode to the donor at reverse bias and decreased the J_ph value. In contrast, H3 with a short π-linker showed amorphous morphology in thin films because of weaker intermolecular interactions, lowering the J_d value in both planar heterojunction (PHJ) OPDs and bulk heterojunction (BHJ) OPDs. The BHJ OPDs with H3 exhibited a broadband EQE value of 64% at 530 nm, a low J_d value of 1.8 × 10⁻⁸, and a high J_ph value of 9.6 × 10⁻³ A cm⁻² at −3 V bias.