Unraveling Mechanistic Differences in Optical and Electrical Sensors: Time-Resolved Operando UV–Vis Spectroscopy of p-Type Perovskite Gas Sensors

To gain a deeper understanding of p-type chemiresistive and gasochromic sensor materials, LaFeO3 and SmFeO3 were investigated by using time-resolved operando UV–vis spectroscopy. A qualitative match in the electrical conductance and optical absorbance below the band edge was observed. The two properties are connected by changes in the electron hole concentration caused by the sensor surface reaction with ethanol, leading to a decrease in both conductance and free carrier absorption. Quantitative differences between the conductance and free carrier absorption behavior are explained based on surface effects caused by the surface band bending and surface adsorbates, which lead to significant changes in conductance but are only of minor importance for changes in the free carrier absorption. Our results demonstrate the potential of time-resolved operando UV–vis spectroscopy to develop a detailed mechanistic understanding of chemiresistive and gasochromic sensors by discriminating between surface and bulk effects and to combine their use for future gas sensor development.