A Direct surface modification strategy of ITO anodes enables high-performance organic photodetectors

Abstract

Organic photodetectors (OPDs) have received great interest for their tremendous potential in the field of optical communication, medical monitoring and intelligent buildings. Interface layers are commonly introduced between the electrodes and active layer of OPDs, to facilitate charge extraction and increase reverse charge injection, thus achieving low dark current density (J_d) and high specific detectivity (D*). However, high preparation cost and hygroscopicity of the interface layer limit their further development in practical applications. Herein, we report a direct modification strategy of the indium tin oxide (ITO) anode to construct high-performance OPDs. The ITO anode modified by dilute hydrochloric acid (ITO-Cl) increases the work function and surface hydrophobicity of the substrate due to the surface coverage of Cl atoms. Using ITO-Cl as the anode, the shifted work function increases the electron injection barrier from the anode to the active layer and the enhanced surface hydrophobicity induces a more favorable vertical stratification morphology of the active layer deposited on the anode surface. As a direct consequence, the OPD device based on the ITO-Cl anode exhibits an ultra-low J_d of 0.90 nA cm⁻² at −1 V bias and high peak D* of 2.31 × 10¹² cm Hz^1/2 W⁻¹ (or 1.79 × 10¹³ cm Hz^1/2 W⁻¹ calculated from the shot noise), which is superior to the control device based on traditional anode ITO/poly(3,4-ethylenedioxythiophene):poly-styrene sulfonate (PEDOT:PSS) due to the effective reduction of the dark current. These results demonstrated that the ITO chlorination strategy is a competitive candidate for developing high-performance OPDs.