MXenes have demonstrated exceptional performance in energy applications, yet their potential in photovoltaic systems, particularly in lead-free perovskite solar cells (PSCs), remains underexplored, with no strategic studies addressing how MXene composition influences critical photovoltaic performance. Here, we present the first strategic screening of MX-type MXenes (including HfCT, ZrCT, TaCT, NbCT, MoCT, and VCT) for rational heterojunction design with CsAgBiBr, focusing on the interplay between properties of MXenes and photovoltaic performance. Density functional theory (DFT) calculations reveal that MXenes can induce substantial electronic states near the Fermi level, creating superior charge transfer paths in CsAgBiBr, with VCT exhibiting the lowest interfacial contact barrier and the highest carrier transfer efficiency. Complementary ab initio molecular dynamics (AIMD) simulations coupled with X-ray photoelectron spectroscopy analyses further demonstrate that the functional termination groups like ─F in MXenes effectively passivate Br vacancies in CsAgBiBr, thereby enhancing crystallization and suppressing defect densities. Consequently, the experimental results yielded a trend in line with the calculations, and the power conversion efficiency (PCE) of the device with VCT represented a 36% improvement, accompanied by exceptional stability. By establishing quantitative structure-property relationships between MXenes and CsAgBiBr, this work provides a universal materials selection paradigm for developing high-performance, environmentally-friendly photovoltaic technologies.