Hourglass-shaped GaAs0.99Bi0.01 nanowire solar cells with CuI-PEDOT:PSS double hole transport layers for enhanced photovoltaic performance

III-V nanostructure-based solar cells (SCs) have emerged as promising contenders for next-generation photovoltaic technologies due to their inherent antireflective properties and the pronounced excitation of optical resonance modes. Nonetheless, the high surface to volume ratio inherent to nanowires (NWs) typically leads to significantly low effective minority carrier lifetimes. Although radial junction architectures were introduced to mitigate this limitation, their experimental efficiencies remain lower than those of axial counterparts, primarily due to challenges in achieving uniform core-shell doping while maintaining low interfacial defect densities. To mitigate these limitations, we propose a core-shell heterojunction NW-SC comprising an hourglass (HG)-shaped GaAs_0.99Bi_0.01 core, conformally coated with a PEDOT:PSS/CuI shell. The proposed structure was simulated using the finite-difference time-domain (FDTD) and CHARGE modules of Lumerical software to evaluate its optical and electrical performance. Optical simulation results utilizing the FDTD module demonstrate that incorporating CuI as a hole-selective layer enhances optical absorption characteristics in GaAs_0.99Bi_0.01 NWs, and an optimized shell thickness minimizes the core material usage without compromising ideal current density, thereby lowering material usage and eliminating the need for additional epitaxial shell growth. Our 3D DEVICE simulations demonstrate that the proposed heterojunction structure can achieve a power conversion efficiency (PCE) of ∼29% when configured with a core p-type doping concentration of 5 × 10¹⁸ cm^-3, a minority carrier lifetime ([Formula: see text]_p) of 40 ns, and a surface recombination velocity (SRV) of 10⁵ cm/s at the CuI/GaAs_0.99Bi_0.01 interface. This validates its high-efficiency operation even under low carrier lifetime conditions. These findings indicate that the proposed design is a promising and potentially fabrication efficient alternative to conventional epitaxially grown core-shell NW-SC architectures.