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

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.