Enhanced performance of dye-sensitized solar cells based on TiO2 with NIR-absorption and visible upconversion luminescence

TiO2 with NIR-absorption and visible upconversion luminescence (UC-TiO2) is prepared by a sol–gel method and calcined at 700 °C for 6 h. The material broadens the response region of dye sensitized solar cells (DSSCs) from an ultraviolet–visible region to the whole region of the solar spectrum. It shifts NIR sunlight to visible light which matches the strong absorbing region of the dye (N719). DSSCs based on UC-TiO2 achieved higher conversion efficiency than that on raw TiO2. UC-TiO2 was mixed with commercial raw TiO2 as additive, and the short-circuit current density, open-circuit voltage and conversion efficiency of the DSSC reached to the optimum values 13.38 mA/cm2, 0.78 V and 6.63% (AM1.5 global), comparing with the blank values: 7.99 mA/cm2, 0.75 V and 4.07%, respectively. Also the mechanisms of upconversion by multiphoton absorption and energy transfer processes are interpreted in this paper.