Silver doped lanthanum phosphate (LaPO4:Ag) nano-composite was successfully synthesized at various concentrations of silver using wet chemistry. The newly synthesized particles were used in the solar absorber medium of thin-film organic solar cells to assist in photons harvesting. The photoactive layer of the solar cell was composed of poly-3-hexylthiophene(P3HT) and (6-6) phenyl-C61-butyric acid methyl ester (PCBM) molecules blend with a small concentration of LaPO4:Ag by weight. The solar cells were fabricated in an inverted device architecture consisting of layers of materials as ITO/ZnO/P3HT:PC61BM-LaPO4:Ag/MoO3/AL. As a result, significant power conversion efficiency was recorded as high as 5.23% using the newly synthesized nano-composite at a silver concentration of 0.05 mol. This is an excellent achievement for ambient device preparations conditions which is over 124% growth in PCE compared to undoped devices. The incorporation of LaPO4:Ag into the polymers blend absorber layer is expected to broaden optical absorption and enhance photons harvesting. The inclusion of silver in the composite could also be expected to trigger surface plasmon resonance effect. Moreover, LaPO4:Ag doped solar cells appeared to be highly stable under ambient environment. The optical and morphological properties of the nano-composite are well presented and discussed.