In this paper, the effect of p–n junction additives via blending p-type semiconductors (NiO and CuI) with n-type TiO2 in polymer electrolyte on quasi-solid-state DSSCs is studied. The conduction mechanism of DSSCs modified with random p–n junctions has been investigated by FTIR, SEM, UV–Vis and electrochemical analysis. The results indicate that the CuI–TiO2 p–n blend modified polymer electrolyte reaches the maximum ionic conductivity of 6.44 mS cm−1, which is almost twice over than that of pure-TiO2 modified one. From photovoltaic study, it is found that introducing CuI–TiO2 and NiO–TiO2 p–n blends in polymer electrolyte can obviously improve electron recombination and light-to-electric conversion efficiency of DSSCs. The conversion efficiency of CuI–TiO2 p–n blend modified DSSC is 3.34%, which is much higher than that of pure TiO2 modified device (1.76%). It is also demonstrated that the photovoltaic properties of DSSCs directly depends on the ratio of p-type CuI and n-type TiO2 in the p–n blends and the optimal conversion efficiency of 4.27% is obtained at CuI:TiO2 ratio of 4:1.