The dynamics of photogenerated carriers and mobile ions in operational cesium lead halide (CsPbI3) perovskite solar cells (PSCs) under working conditions are studied using nanoscale-resolved fluorescence lifetime imaging microscopy (FLIM). The temporally and spatially resolved photoluminescence (PL) changes in the perovskite film during and after bias light soaking are dynamically monitored. Through the analysis of the dynamic variations of PL intensity and PL lifetime of an open-circuit PSC, the impacts of light soaking are revealed by a dynamic model of photogenerated charge carrier and mobile ions. We confirmed the different behaviors between morphological domain interiors and domain boundaries during light soaking, which shed light on the engineering of the domain interiors in addition to the commonly considered domain boundary strategies. This work provides a full picture of the photogenerated process in an operational PSC and therefore guides the design and operation of perovskite-based optoelectronic devices.