As the core structure of kesterite thin-film solar cell (TFSC), the nature of N-type functional layer and its interface is a key issue impacting device performance, typically its influence on carrier recombination and electron charge transportation. Here, a modified window layer to tailor N-type bulk and its interface properties for efficiency carrier collection and device performance is incorporated by co-sputtering ZnO and SiO2. Research has found that the modified window layer not only has an excellent wide optical spectrum with high transmittance, enabling additional photon harvesting and short-wave absorption, but also modulates the energy band position for better band alignment to facilitate charge transportation, ensuring higher conductivity. Simultaneously, the significantly reduced carrier recombination and increased uniformity of the device further accelerate charge efficient collection and enhance filling factor (FF). Consequently, the modified window layer of kesterite TFSC enables a remarkable efficiency improvement from 8.4% to 12.0% with a boosted FF from 61% to 73%. These novel results provide the inherent physical origin for improving the photovoltaic performance of kesterite TFSC by appropriate modification of ZnO:SiO2 window layer and open up an effective and feasible strategy, which can also be applied to other optoelectronic devices.