Research advances in bipolar spectral response photodetectors and their applications

With the development of the information age, the demand for compact, multifunctional, and low-power photodetectors has become increasingly urgent. Traditional photodetectors, constrained by a unipolar photocurrent response (solely positive or negative), face fundamental limitations in dynamically processing complex optical information. Bipolar spectral response photodetectors have emerged as a revolutionary class of devices, distinguished by their unique capability to exhibit wavelength-dependent bidirectional modulation of photocurrent. This means the sign of the generated photocurrent (positive or negative) can be dynamically switched simply by altering the incident light wavelength. This intrinsic property transcends the functional boundaries of conventional detectors, unlocking novel physical mechanisms and forging innovative technological pathways for the sophisticated manipulation and processing of optical signals. This unique bidirectional response capability unlocks immense potential for developing a new generation of advanced optoelectronic applications that were previously challenging or impossible with unipolar devices, such as novel optoelectronic logic gates where wavelength directly programs Boolean functions (AND, OR, NOR, NOT, and NAND) at the device level, optical communication encryption schemes leveraging wavelength-specific current polarity as physical encryption keys to drastically enhance security against eavesdropping, advanced spectral imaging encoding techniques utilizing photocurrent sign as an additional information dimension, and biomimetic visual perception systems that mimic biological vision’s ON/OFF pathways for adaptive contrast adjustment. This paper provides a comprehensive review of the latest, groundbreaking research progress within the burgeoning field of bipolar spectral response photodetectors. We first delve into the fundamental working mechanisms including band engineering regulation (precise control over the band alignment in heterostructures), physical effect coupling (leveraging phenomena like the photovoltaic effect, plasmonic effect, photo-thermoelectric effect, photogating effect, and radiative thermal effect), deliberate defect state or surface state induction acting as photonic energy-selective carrier traps or recombination centers, photoelectrochemical-assisted carrier transfer governed by semiconductor-electrolyte interfacial energetics, etc. Subsequently, we elaborate on the significant application potential of bipolar spectral response photodetectors across the aforementioned cutting-edge domains, highlighting representative research breakthroughs and proof-of-concept demonstrations that showcase their transformative capabilities. We analyze the prevailing challenges hindering the practical deployment of current bipolar spectral response photodetectors. These challenges encompass optimizing performance trade-offs, overcoming material stability issues, addressing complexities in device fabrication and large-scale integration compatibility, and enhancing long-term operational robustness, especially for surface-state-dependent mechanisms susceptible to ambient contamination or liquid-electrolyte-based systems facing evaporation, leakage, or electrochemical drift. Finally, three dimensions are critical for future advancement: breakthroughs in fundamental mechanisms and materials, comprehensive performance optimization, and innovative application expansion. The synergistic advancement across these dimensions is paramount for translating laboratory breakthroughs into practical technologies. By synthesizing the current state of knowledge, identifying key hurdles, and outlining promising avenues for material innovation, device design, and system application, this review aims to establish a solid theoretical foundation and provide practical methodological guidance for designing and realizing the next generation of intelligent, multi-functional optoelectronic systems centered on bipolar spectral response technology.