• Chemical adsorption of 4- tert -butylpyridine (4-TBP); 2,2′-bipyridine on TiO 2 surface. • One third of V oc increase due to the adsorption of 4-TBP to the TiO 2 surface. • Remaining V oc increase due to effects of 4-TBP on the electrolyte mediator. We have investigated the binding of two electrolyte additives, 4- tert -butylpyridine (4-TBP) and 2,2′-bipyridine (bipy), to the surface of TiO 2 photo-anode by attenuated total reflection – Fourier transform infrared spectroscopy (ATR-FTIR); X-ray photoelectron spectroscopy (XPS); zeta potential; cyclic voltammetry analyses, and explained how the adsorption affects photovoltaic performance of dye-sensitized solar cell (DSC). To clarify whether the adsorption of 4-TBP/bipy on TiO 2 surface affects the DSC performance, DSC devices were fabricated with non-grafted and 4-TBP or bipy grafted TiO 2 photo-anodes, with application of two types of electrolytes with and without the nitrogen additives. Furthermore, the interaction between 4-TBP or bipy with the electrolyte mediator I−/I 3 − was investigated by cyclic voltammetry. The results showed that 4-TBP and bipy were able to bind chemically to TiO 2 surface at elevated temperatures. DSC prepared with N-additive grafted TiO 2 photo-anodes had lower short current and efficiencies than non-grafted cells. The open circuit voltage (V oc) was, however, increased 110 mV for 4-TBP grafted cells with 0.5 M 4-TBP in the electrolyte. One third of the overall increase in V oc was estimated to be due to the adsorption of the 4-TBP to the TiO 2 surface. The remaining V oc increase was due to effects of 4-TBP on the electrolyte mediator. [ABSTRACT FROM AUTHOR]