Wet chemistry was employed to synthesis tri-metals nano-composite containing cerium, cobalt and calcium (Ce:Co:Ca). The optical and morphological properties exhibited by the synthesized nano-composite were found to be favourable for photovoltaic device applications. Consequently, the introduction of Ce:Co:Ca nano-particles in the P3HT:PCBM blend photo-active medium resulted in improved power conversion efficiency (PCE) by 104 % compared to the pristine active layer. The results unveil a new progress in achieving high overall solar cell performance through the use of triple metals composite local surface plasmon resonance (LSPR) effect and possible light trapping mechanism in the absorber layer. Furthermore, it was noted from the investigation that device performance is dependent on the particles concentration which was varied from 0 % to 3 % by weight. The optimum NPs concentration for the best power conversion efficiency was 3 wt% that produced a PCE of 5.3 % which is an important development for open-air device preparation condition. The metals nano-particles were studied using various spectrometers such as high-resolution scanning and tunnelling electron microscopy (HRSEM and HRTEM); energy dispersion X-ray (EDX); and X-ray diffraction (XRD) etc. All results are clearly presented and discussed in the manuscript.