Organic cations in hybrid organic-inorganic perovskite solar cells are susceptible to decomposition under high temperatures and ultraviolet light, leading to a decline in power conversion efficiency (PCE). All-inorganic perovskite solar cells exhibit both high PCE and superior photothermal stability, making them promising candidates for single-junction and tandem photovoltaic applications. The mixed-halide perovskite CsPbI₂Br has garnered significant attention as a top cell in semi-transparent and tandem solar cells owing to its excellent thermal stability and suitable bandgap (1.90 eV). Although the PCE of CsPbI₂Br-based solar cells is nearing its theoretical limit, the non-radiative recombination-induced energy losses remaining a major barrier to further performance enhancement. This non-radiative recombination is primarily caused by inadequate band alignment between the absorption layer and the transport layer, resulting in open-circuit voltage (V_OC) losses and reduced short-circuit current density (J_SC). Two-dimensional perovskite passivation formed via solution processing could mitigate interfacial recombination, but it also could impede efficient charge transport. Constructing three-dimensional perovskite structures not only provides an effective solution to these limitations but also enhances sunlight absorption and facilitates carrier transport. In this study, we propose a Dual-absorption-layer Perovskite Heterojunction (DPHJ) strategy, which involves integrating a staggered type-II perovskite heterojunction (p-pCsPbI₂Br-CsPbIBr₂) into the absorption layer of the top cell in an all-perovskite tandem solar cell. The result of simulation indicates that stacking a 100 nm-thick CsPbIBr₂ layer atop a 300 nm-thick CsPbI₂Br layer significantly enhances the PCE of the single-junction device from 19.46% to 22.29%. This improvement is primarily attributed to band bending at the CsPbI₂Br/CsPbIBr₂ interface, which enhances the built-in electric field, facilitates carrier transport, and suppresses non-radiative recombination within the absorption layer. Compared with the tandem solar cell utilizing a single-absorption-layer CsPbI₂Br top cell, the DPHJ-based tandem solar cell significantly increases the V_OC (from 2.16 V to 2.25 V) and enhances the J_SC (from 15.96 mA×cm^-2 to 16.76 mA×cm^-2). As a result, the DPHJ-based tandem solar cell achieves a high theoretical PCE of 32.47%. In addition, the DPHJ-based tandem solar cell exhibits a significantly enhanced external quantum efficiency in the 500-580 nm wavelength range, which could be attributed to the band-edge absorption of CsPbIBr₂. This enhanced absorption generates more photogenerated carriers, thereby significantly improving the J_SC. The results of this study surpass the experimentally reported V_OC and PCE values of current CsPbI₂Br single-junction and all-perovskite tandem solar cells. Further experimental results show that compared with the single-layer CsPbI₂Br (E₂= 101.9 meV, electron-phonon coupling strength γ_ac=1.2×10^-2，γ_LO=6.9×10³), the double-absorption-layer film exhibits a higher exciton binding energy (E₂= 110.7 meV) and reduced electron-phonon coupling strength (γ_ac=1.1×10^-2，γ_LO=6.3×10³), which helps suppress phase segregation and enhances both optical and thermal stability—favorable for fabricating long-term stable all-perovskite tandem solar cells. By focusing on absorption layer design, this work provides new insights and theoretical guidance for enhancing the efficiency and stability of all-perovskite tandem solar cells. It presents a versatile design concept for optimizing absorption layers in all-perovskite multijunction cells and is expected to drive further advancements in this field.