Enhancing Dark Current Suppression in Near‐Infrared Organic Photodetectors with Morphology Control and Self‐Assembled Monolayers

Abstract This study addresses the challenges of high dark current density and low responsivity in near‐infrared organic photodetectors (NIR‐OPDs) through a synergistic strategy combining morphology control and interface engineering. A thick active layer incorporating solid additives effectively reduces the dark current density while preserving efficient charge transport. Subsequently, molecular interface modification using [2‐(9HCarbazol‐9‐yl)ethyl]phosphonic acid (2PACz) further suppresses the dark current and enhances photoresponsivity. Drift‐diffusion modeling, incorporating trap states, reveals that the 2PACz forms a dipole layer at the interface, lowering the injection barrier by ≈0.3 eV and eliminating traps within the device. Together, these strategies reduce the dark current density from the order of 10⁻⁵ A cm⁻² (control) to the order of 10⁻⁸ A cm⁻² at −1 V, and enhance the responsivity (R) from 0.50 A W⁻¹(control) to 0.58 A W⁻¹ at 864 nm. The resulting device exhibits a high shot‐noise‐limited specific detectivity (D_sℎ^∗) reaching 9.57 × 10¹³ Jones, highlighting its exceptional sensitivity. This study demonstrates that combining morphology control with interface engineering effectively overcomes key performance limitations in NIR‐OPDs, providing valuable insights for the design of high‐performance organic photodetectors.