Abstract
lack phosphorus (BP), a direct-bandgap two-dimensional (2D) semiconductor, features a uniquely tunable bandgap ranging from ~0.3 eV in the bulk to ~2.0 eV in the monolayer, along with a high carrier mobility of up to 1000 cm²·V⁻¹·s⁻¹. This positions BP as a promising material that bridges the gap between zero-bandgap graphene and low-mobility transition metal dichalcogenides (TMDs, ~100 cm²·V⁻¹·s⁻¹). Although BP is thermodynamically the most stable allotrope of phosphorus, it undergoes irreversible oxidation in oxygen-rich or electron-accepting environments. This degradation is primarily driven by the lone-pair electrons on phosphorus atoms, which promote the formation of P–O bonds and disrupt the in-plane P–P covalent network, ultimately compromising structural and electronic integrity.
To overcome this challenge, an electrochemical intercalation and in situ electrochemical deposition (EI&ED) technique was developed to fabricate scalable Au nanoparticles/FL-BP (Au/FL-BP) composites with significantly enhanced environmental stability. This method suppresses the chemical reactivity of BP by enabling efficient local charge transfer from FL-BP to electrochemically deposited Au nanoparticles (AuNPs). The resulting Au/FL-BP composites exhibit remarkable stability in harsh environments, including: i) sustained high humidity (95% relative humidity); ii) prolonged immersion in organic solvents (up to 45 days); iii) thermal annealing at elevated temperatures (573 K for 9 hours). Moreover, Au/FL-BP-based photodetectors demonstrate 50- and 36-fold enhancements in photoresponsivity at 1550 nm and 1850 nm, respectively, driven by surface plasmonic effects.
While the improved stability of FL-BP is a crucial milestone, its dispersed nature limits large-area device fabrication and integration. To address this limitation, the concentration of FL-BP dispersions was increased, followed by diffusion and self-assembly under surface tension gradients, solute concentration gradients, and Marangoni flow-induced interface capture effects. This process enabled the formation of continuous, uniform BP films. The films' high-quality characteristics were confirmed through optical microscopy, Raman spectroscopy, and atomic force microscopy.
iii
BP’s high specific surface area, unique electrical properties, and sensitivity to optical modulation make it ideal for sensor applications. An all-solid-state, high-performance humidity sensor was fabricated using a solution-processable, large-area AuNPs-BP composite thin film. The device achieved a sensitivity of up to 2000% under 30°C and 85% RH. Notably, during continuous testing over two weeks, the sensor demonstrated excellent stability under various conditions, including low temperatures (15°C), high temperatures (60°C), and strong light irradiation across wavelengths from 532 nm to 1550 nm. These results highlight the potential of AuNPs-BP composite films for robust humidity sensing in diverse and harsh environments.
In summary, advancements in BP stabilization (via EI&ED), scalable film fabrication, and multifunctional device demonstrations (sensors, photodetectors) underscore its versatility for next-generation optoelectronics. Future work will focus on optimizing large-scale production, integrating BP into flexible systems, and exploring new applications in wearable technology and harsh-environment monitoring.