An experimental and simulation approach was used to investigate the impact of copper （Cu） content （Cu/In+Ga， CGI） in nanoparticles ink on the performance of copper indium gallium selenide selenium （CIGSSe） solar cells. Firstly， CIGSSe solar cell devices was prepared using different CGI inks and their absorber layers were characterized using scanning electron microscopy （SEM）， Hall effect measurements， and Raman spectroscopy. The results showed that as the copper content increased， the crystal growth of the absorber layer gradually improved， and the carrier concentration increased. However， the Cu_2-xSe phase became more prominent on the surface. The best experimental conversion efficiency was achieved with CGI of 1.03， and a photovoltaic conversion efficiency of 10.09%. Then a corresponding device simulation model was established to obtain the photoelectric conversion performance， device band structure， and recombination rate distribution of CIGSSe devices with different CGI. The simulation results showed that as the copper content increased and the carrier concentration increased， the open-circuit voltage of the device increased. However， when the carrier concentration exceeded 10¹⁸ cm^-3， a steep band bending phenomenon appeared on the absorber layer surface， which increased the occurrence of tunneling interface recombination， thereby affecting the device efficiency. Therefore， both the experimental and simulation results suggested that it could be necessary to control the Cu content when preparing CIGS thin-film solar cells to promote crystal growth， reduce interface recombination， and improve device efficiency.