Solution‐Processed Lead Sulfide Quantum Dots‐Based Self‐Powered Transient Photodetectors for Bidirectional Weak‐Light Communication up to 1550 nm

ABSTRACT Reliable optical communication across the ultraviolet (UV) to short‐wave infrared (SWIR) spectrum remains challenging due to the complexity of multicomponent photodetectors, high dark current, limited weak‐light sensitivity, and difficulty in achieving bidirectional operation. Here, we report a solution‐processed PbS colloidal quantum dot (PbS‐CQD)‐based MSIM transient photodetector (TPD) for highly sensitive, self‐powered optical communication employing on‐off keying (OOK) and four‐level pulse amplitude modulation (PAM‐4). The engineered PbS‐CQDs exhibit broadband absorption extending from the UV to the 1550 nm telecommunication window. A dual‐transparent electrode architecture (ITO/PEDOT:PSS/PbS‐CQDs/ionic liquid gel/ITO) enables efficient bidirectional photodetection under illumination from both directions. The ionic liquid gel forms an interfacial electric double layer that facilitates efficient charge separation and accumulation without external bias, resulting in negligible dark current and stable operation. The device demonstrates fast transient response times of 3.12 and 8.58 µs, a modulation bandwidth of ∼168.9 kHz, and a high signal‐to‐noise ratio of ∼40 dB, while operating effectively under µW/cm 2 illumination. A proof‐of‐concept ASCII‐based communication system confirms reliable OOK and PAM‐4 data transmission from UV to SWIR wavelengths, highlighting the device's potential for low‐power broadband optical communication and next‐generation telecommunication technologies, distributed photonic sensing, and fiber‐optic systems.