Upconverted Nanophosphors for Increasing Efficiency in a Dye-Sensitized Solar Cell

Upconverting nanoparticles has a significant potential to enhance solar cell efficiency as a "spectral converter". Here, we report a phase pure, cubic, upconverting BaGdF5:Er/Yb-doped nanocrystal accessible via ionic liquids that are combined with TiO2 to apply as the absorption layer in a dye-sensitized solar cell (DSSC) as a potential technology to harvest solar energy. Bright-green (520 and 540 nm) and red (665 nm) emissions were observed due to transitions of 2H11/2 + 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2, respectively. The experimental data for 540 and 665 nm emission bands of BaGdF5:Er3+/Yb3+ nanoparticles have been fitted with a straight line with a slope of ∼2, which confirms the two-photon absorption process. It is also found that not only the overall upconversion intensity but also the IG/IR ratio has a significant effect on device efficiency. Under 1 sun illumination, cells fabricated with the BaGdF5:Er3+(1%)/Yb3+(10%)/TiO2 absorption layer showed the highest photon conversion efficiency (PCE) of 7.75% with current density Jsc = 15.9 mA/cm2. However, when only TiO2 is used as the absorption layer, a much lesser PCE of 4.60% along with Jsc = 9.6 mA/cm2 is obtained. Almost a 68.47% enhancement in photon conversion efficiency and a significant increase in current density (Jsc) (65.62%) for the BaGdF5:Er3+(1%)/Yb3+(10%)/TiO2-based device compared to the bare TiO2 cells promise the potential use of upconverting materials as a spectral converter in the DSSC and other solar cell devices.