Lead-free halide perovskites (LFPs) are quickly gaining popularity as alternatives to harmful lead-based perovskites. However, widespread use is hampered by low power conversion efficiency (PCE). Here, we report a comprehensive simulation study on an unconventional double perovskite absorber, Cs2AgBiBr6, within a standard n-i-p device architecture. The simulations were carried out using CNTS as the common HTL, while different ETLs were explored: (1) AZnO, yielding the highest efficiency having VOC of 1.375 V, JSC of 21.37 mA/cm2, FF of 80%, and PCE of 23.50%; (2) CdZnS, achieving VOC of 1.372 V, JSC of 21.41 mA/cm2, FF of 78.82%, and PCE of 23.15%; and (3) LBSO, resulting in VOC of 1.373 V, JSC of 21.40 mA/cm2, FF of 79.72%, and PCE = 23.42%. In all cases, Cs2AgBiBr6 served as the absorber layer. These findings provide a potential route for the rational design of efficient and stable LFPs solar cells.