Dopant-Assisted Exciton Enhancement: Improved Photoelectric Performance in Copolymer-Based Photodiodes

Abstract

Copolymers organic semiconductors (OSCs) such as diketo pyrrolopyrrole-thieno[3,2-b]thiophene (DPPT-TT) have demonstrated strong peak absorption in ultraviolet (UV) and near-infrared (NIR) regions. However, OSC-based photodiodes (OPDs) still suffer from low photodetection efficiency and photocurrent due to the high recombination rate of Frenkel excitons and limited light absorption caused by the thin active layer. In this work, a dopant-assisted exciton enhancement (DEE) mechanism is explored. By introducing a dopant layer between the bottom electrode and active layer, charge transfer is driven, significantly suppressing exciton recombination, resulting in more than a ten-fold increase in photodiode responsivity. To further enhance light absorption, a layer of metal particle nanostructure is employed. The fabricated OPDs exhibit significantly improved photoelectric performance, achieving a photocurrent density of 15.83 mA/cm2 under a light intensity of 0.002 W/cm2 at 264 nm. The external quantum efficiency (EQE) reaches approximately 98.41% at a bias voltage of 2 V, which is a 27-fold increase compared to conventional devices. Experimental results demonstrate that thin organic photodetectors, modified by electrophilic substitution and light scattering principles, hold great potential for nonvisible light band detection.