High-Efficiency Hexagonal Nanowire MAPbI3 Perovskite Solar Cell with Broadband Light Trapping

Perovskite solar cells (PSCs) have emerged as strong contenders for the next generation of photovoltaic (PV) technologies due to their exceptional light absorption properties, tunability, and affordability in manufacturing. Here, we presented an ingenious hexagonal nanowire (HNW)-based PSC that achieves broadband absorption, minimizes reflectance, and offers robust polarization insensitivity by improving light-matter interaction and increasing charge-collection efficiency. The rotational symmetry of the HNW configuration yielded polarization-independent absorbance under both TE and TM illumination across the visible and near-infrared spectra. The optimization of the geometrical parameters of CH3NH3PbI3-based HNW structure, including diameter, period, and fill ratio, offered a wide rangeof variations that influenced both optical properties and device performance. To further intensify photon confinement, a dielectric SiO2 sphere is partially embedded in the ITO layer, improving long-wavelength absorbance and increasing electron-hole pair generation near the active region. We analyzed the finite-difference time-domain (FDTD) method to examine the optical properties of our proposed structure. This study demonstrates that our proposed structure has achieved a higher generation rate, enhanced absorbance, and a higher optical short-circuit current density (Jsc) of 29.53 mA/cm2. Electrical performance is assessed by solving the coupled drift-diffusion and Poisson equations for the dynamics of carrier transport. The optimized HNW structure achieved a notable power conversion efficiency of 24.2%, highlighting a strong connection between optical confinement and effective carrier transport. These attributes render the proposed HNW PSC a viable option for high-performance PV systems and scalable thin-film solar technologies.

💡 Research Summary

This paper introduces a novel architecture for methylammonium lead iodide (MAPbI₃) perovskite solar cells that leverages a hexagonal nanowire (HNW) array combined with a partially embedded SiO₂ sphere to achieve broadband light trapping, polarization‑independent absorption, and high charge‑collection efficiency. The authors first motivate the need for improved light‑matter interaction in perovskite photovoltaics, noting that conventional planar or mesoporous designs suffer from limited spectral coverage, polarization‑dependent response, and complex multilayer stacks. By arranging MAPbI₃ nanowires in a hexagonal lattice, the structure inherits six‑fold rotational symmetry, ensuring identical optical behavior under transverse electric (TE) and transverse magnetic (TM) illumination across the visible and near‑infrared range.

Geometrical parameters—nanowire diameter (D), period (P), and fill ratio (FR = D/P)—are systematically varied using three‑dimensional finite‑difference time‑domain (FDTD) simulations (Ansys Lumerical). A non‑uniform mesh of 0.25 nm and 64 perfectly matched layers (PML) guarantee numerical accuracy. The optimal configuration is identified as D = 300 nm (radius = 150 nm) with FR between 0.5 and 0.9, which yields a nearly flat absorbance above 90 % from 450 nm to 800 nm. The broadband response is attributed to enhanced photonic coupling, extended optical paths within the nanowires, and the excitation of Mie resonances.

To further boost long‑wavelength absorption, a dielectric SiO₂ sphere (diameter comparable to the nanowire spacing) is introduced in two ways: placed on top of the indium‑tin‑oxide (ITO) electrode or partially embedded within the ITO layer. The sphere acts as an optical concentrator, scattering incident photons into the nanowire region and reducing reflectance, especially beyond 700 nm. The embedded configuration provides an additional 5 % improvement in absorbance at the longest wavelengths, as confirmed by the FDTD field maps.

The optical results feed into an electrical model that solves Poisson’s equation together with the drift‑diffusion equations for electrons and holes. Carrier mobilities (μₙ ≈ 10 cm² V⁻¹ s⁻¹, μₚ ≈ 5 cm² V⁻¹ s⁻¹) and diffusion coefficients are linked via the Einstein relation. Non‑radiative Shockley‑Read‑Hall recombination is included with lifetimes τₙ = τₚ = 1 µs. Assuming unit internal quantum efficiency, the calculated short‑circuit current density reaches J_sc = 29.53 mA cm⁻², the open‑circuit voltage is V_oc ≈ 1.32 V, and the fill factor is about 0.71, resulting in a power conversion efficiency (PCE) of 24.2 %. This performance surpasses typical planar MAPbI₃ cells (≈21 %) and is competitive with more complex 3D/2D heterostructures that report ≈23 % efficiency, while avoiding their fabrication intricacies.

Analysis of the carrier generation rate G(x,y,z) shows peaks at the nanowire cores and around the SiO₂ sphere, indicating that the geometry not only traps light but also directs the generated carriers toward the TiO₂ electron‑transport layer and the Spiro‑OMeTAD hole‑transport layer. The electric‑field distribution confirms strong field concentration within the nanowire gaps, which accelerates charge extraction and suppresses recombination.

Finally, the authors discuss practical routes to fabricate the proposed structure. Hexagonal nanowire arrays can be realized by nanoimprint lithography, interference lithography, or self‑assembly of templated polymer scaffolds followed by MAPbI₃ solution infiltration. The SiO₂ spheres can be deposited via colloidal spin‑coating and then partially embedded by controlled etching of the ITO layer or by atomic‑layer deposition (ALD) of ITO over the spheres. These processes are compatible with existing perovskite spin‑coating workflows and can be scaled to large‑area modules without substantial cost increase.

In summary, the work demonstrates that a hexagonally ordered MAPbI₃ nanowire array, enhanced with a strategically placed SiO₂ sphere, provides a synergistic combination of broadband, polarization‑insensitive light absorption and efficient charge transport, delivering a simulated 24.2 % PCE. The study offers a clear design guideline for next‑generation perovskite photovoltaics that aim for high efficiency, manufacturability, and stability.