<p>Two-/three-dimensional (2D/3D) perovskite solar cells combine strong light absorption with excellent charge transport; however, their device performance remains highly sensitive to interfacial recombination and imperfect energy level alignment. In this work, we evaluate a dual-hole-transport-layer (HTL) strategy for this kind of perovskite stack based on MAPbI₃ and a thin PEA₂PbI₄ 2D capping layer using SCAPS-1D. A broad screening of organic and inorganic dual HTLs is conducted, with emphasis on HTL ordering and its impact on band alignment and carrier extraction. The simulations show that HTL ordering is decisive, and that placing an inorganic HTL adjacent to the perovskite while keeping Spiro-OMeTAD as the outer HTL can reduce interfacial losses and increase the fill factor and current density. Among the tested combinations and optimization strategies, the CuO/Spiro-OMeTAD bilayer provides the highest simulated performance, reaching peak power conversion efficiency of 29.97% under the chosen model parameters. Analysis of the 2D/3D interface defect density (<i>Nt</i>) of the optimal dual-HTL (CuO/Spiro-OMeTAD) device in terms of open-circuit voltage (<i>Voc</i>) sensitivity, thermodynamic efficiency limits, and recombination kinetics reveals a defect-tolerant regime of <i>Nt</i> ≤ 10¹²&#xa0;cm⁻², with a critical threshold of <i>Nt</i> = 10¹⁵&#xa0;cm⁻², identified as the practical limit to prevent significant <i>Voc</i> degradation. These results establish practical design rules for dual-HTL selection and thickness optimization in 2D/3D perovskite devices.</p> Graphical Abstract <p></p>