Near-Infrared Organic Photodetectors with Tailored Junction Thickness for Resonance-Enhanced Photoresponse and Suppressed Dark Current
Yijun Huang, Hao Lu, Lin Shao, Zhaohong Tan, Shuaiqi Li, Sheng Dong, Xiye Yang, Wenkai Zhong, Yazhong Wang, Fei Huang
Abstract
Organic photodetectors (OPDs) based on nonfullerene acceptors (NFAs) offer a promising platform for near-infrared (NIR) detection, yet their performance beyond 1100 nm is often limited by low external quantum efficiency (EQE) due to inefficient exciton dissociation and severe nonradiative recombination in narrow-bandgap systems. In this work, we address these challenges by employing a low-dark-current NFA (QXIC-4F) and tailoring the junction thickness to induce resonance-enhanced absorption. Optical simulations guided the optimization of the active layer to 340 nm, establishing constructive resonance at 1130 nm. As a result, the device achieves an EQE of 23% under −5 V bias, nearly twice that of a nonresonant reference, while maintaining a low dark current density ( J d ) of 1.8 × 10 –8 A cm –2 and a noise current spectral density as low as 10 –16 A Hz –1/2, yielding specific detectivities ( D *) up to 10 13 Jones at zero bias. The thick active layer also suppresses trap-assisted transport, preserving D * above 10 11 Jones under −5 V. All devices exhibit microsecond-scale response times with −3 dB bandwidths of 90 kHz, supporting their potential for high-speed operation. Furthermore, integration onto flexible substrates enables wearable photoplethysmography (PPG) monitoring. This work presents a scalable strategy that leverages optical resonance to simultaneously enhance sensitivity and reduce noise in NIR OPDs, advancing their applicability in biomedical and low-light sensing.