<p>We introduce synchronized modulation Kelvin probe force microscopy (SM-KPFM), an in-operando technique that synchronizes external stimulus modulation, such as illumination or bias, with the scanning direction of the atomic force microscope to minimize artifacts from drift, thermal effects, and probe degradation. In synchronized illumination KPFM, the sample is illuminated during retrace and dark during trace, enabling real-time comparison of surface potentials within a single raster frame. At the example of a silicon photodiode and a molybdenum disulfide bilayer on gold, these superior properties are demonstrated, yielding drift-free, accurate surface photovoltage maps and clearer insights into photovoltaic effects.</p> Graphical abstract <p></p>