Humidity-driven nonlinear modulation of graphene reflectivity via interfacial wetting behavior

Abstract Graphene’s moisture absorption significantly impacts its optical reflectivity, leading to measurement errors in graphene-based optoelectronic devices. The mechanism underlying this humidity effect remains unclear. Here we developed a portable fiber optic Fabry–Perot (F–P) probe with a 10-layer graphene film to in situ investigate the non-monotonic changes in reflectivity across varying humidity conditions. The probe showed a 49.8% modulation range in reflectivity between 8 and 67.5% relative humidity (RH). Wetting experiments and COMSOL simulations reveal that humidity-driven changes in graphene reflectivity are due to droplet diameter growth. From 7.5 to 31.3% RH, increasing droplet size enhances scattering with weak absorption, resulting in a positive reflectivity-humidity correlation. From 31.3 to 66.3% RH, larger droplets reduce scattering and increase absorption, shifting the correlation to negative. We establish a quadratic relationship between reflectivity and humidity, allowing for a corrective method that narrows the operational range to 53.9–58.9% RH, minimizing humidity-induced reflectivity fluctuations. This method defines optimal humidity conditions for stable operation of graphene-based optoelectronic devices and offers a feasible route for probing humidity-sensitive behaviors in other two-dimensional materials.