<p>Enhancing the efficiency of ultra-thin CIGS (copper indium gallium selenide) solar cells remains challenging primarily because their reduced active layer thickness limits sufficient light absorption. This work investigates the use of novel plasmonic metal nanoparticles as an alternative to conventional silver and gold nanoparticles to boost the performance of ultra-thin CIGS devices. Through 3D optical simulations, the effects of embedding single and double elliptical nanoparticles made of silver, aluminum, copper, nickel, and titanium within the CIGS active layer are analyzed. The optimal nanoparticle sizes are determined by maximizing the short-circuit current density (<i>J</i>_sc) originating from absorption within the CIGS layer, while considering the associated parasitic absorption losses within the nanoparticles. Comparing the absorption spectra, electric field profiles, generation rates, and calculated power conversion efficiencies reveals that copper double nanoparticles maintain high short-circuit current density (<i>J</i>_sc) values resulting from optical absorption within the CIGS layer, even when simulated oxidation effects are included, achieving an efficiency of 18.65%, which is very close to 18.78% for silver nanoparticles. This cluster copper nanostructure outperforms previous plasmonic CIGS solar cell designs while utilizing an abundant, low-cost material. The proposed simple yet effective copper nanoparticle configuration presents a promising approach to enhance the performance of ultra-thin film CIGS photovoltaics.</p>