Demand for low-cost, environmentally friendly alternative renewable energy sources makes the dye-sensitized solar cell (DSSC) a viable alternative. DSSCs have a high but competitively challenged power conversion e ffi ciency (PCE) of 11.9 % . Plasmonic DSSCs is one approach with extreme enhancement of light absorption to increasing the PCE. The highest PCE of plasmonic DSSCs is still < 11 % however, due to secondary e ff ects which are not yet well understood. In this study, we used a complex composite of plasmonic nanoparticles (PNPs) with extended characterization and wide ranging PNP loadings, combined with a systematic approach to obtain synergistic e ff ects and a deeper understanding of the e ff ects of plasmonic nanostructures on DSSC performance. The results showed two optimal loading amounts of PNPs with enhanced PCEs of 4.26 and 4.36 % (from 3.54 % ), with enhancement e ff ects obtained mainly from e ffi cient charge injection and a balance of the negative and positive e ff ects of the PNPs, respectively. An increase in the photoanode thickness from 5.5 to 9 ¯ m resulted in PCE enhancement from 4.39 to 4.58 % , mainly via e ffi cient charge injection. The PNPs had both positive and negative e ff ects on key DSSC performance parameters: decreased photoanode surface area but with panchromatic enhancement of light absorbance; increased short circuit current up to a point followed by a decrease due to poor charge injection; increased open circuit voltage and fi ll factor; enhanced charge transfer resistance against charge recombination; improved electron lifetime and charge collection e ffi ciency; lowered enhancement of cell performance in the near infra-red region; and induced abundantly generated electrons augmented charge recombination. These results contribute signi fi cantly to understanding of the e ff ects of plasmonic nanostructures and can serve as a useful guide to the study of plasmonic DSSCs and related fi elds.