The influence of interface modification of sensitized TiO2 surfaces by co-adsorbents on photovoltaic performance is detailed. We investigated different functional groups of co-adsorbents, such as carboxylic (4-guanidino butyric acid, chenodeoxycholic acid), phosphinic (dineohexyl phosphinic acid), and phosphonic (dodecyl phosphonic acid), to better highlight their influence on the device performance and accurately classify them into de-aggregating agents or agents with both de-aggregating and co-adsorbing properties. By optimizing the type of co-adsorbent and its concentration in the dye solution, we reached an efficiency of 11.0% using 4-guanidino butyric acid or dineohexyl phosphinic acid, compared to 10.6% when the benchmark chenodeoxycholic acid was used. The presence of co-adsorbents on the TiO2 surface was studied using ATR-FTIR spectroscopy. The role of these co-adsorbents on the band edge shift versus the recombination resistance is discussed.