Self-Powered Gas Sensor Based on a Photovoltaic Cell and a Colorimetric Film with Hierarchical Micro/Nanostructures

We report a new type of self-powered gas sensors based on the combination of a colorimetric film with hierarchical micro/nanostructures and organic photovoltaic cells. The transmittance of the colorimetric film with micro/nanostructures coated with N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) changes by reacting with NO₂ gas, and it is measured as a current output of the photovoltaic cell. For this purpose, materials for the organic photovoltaic cells were carefully chosen to match the working wavelength of the TMPD. Micropost arrays and nanowires increase the surface area for the gas reaction and thus improve the transmittance changes by NO₂ gas (6.7% change for the plain film vs 27.7% change for the film with hierarchical micro/nanostructures to 20 ppm of NO₂). Accordingly, the colorimetric device with the hierarchical structures showed a response of ΔI/I₀ = 0.27-20 ppm of NO₂, which is a 71% improvement compared to that of the plain sensing film. Furthermore, it showed a high selectivity against other gases such as H₂S and CO with almost negligible responses. Since the current output change of the photovoltaic cell is utilized as a sensor signal, no extra electrical power is required for the operation of gas sensors. We also integrated the sensor device with an electrical module and demonstrated a self-powered gas alarm system.