NaYF4:Yb3+/Er3+ nanorod/TiO2 mesoporous films for enhanced dye sensitized solar cells

Abstract

We synthesized NaYF₄:Yb³⁺/Er³⁺ nanorods (NRs) through a hydrothermal process. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses revealed that these nanorods are composed of smaller NaYF₄:Yb³⁺/Er³⁺ nanocrystals. Subsequent annealing treatments caused these nanocrystals to fuse into larger structures. We incorporated the NaYF₄:Yb³⁺/Er³⁺ NRs into a mesoporous TiO₂ film to create NaYF₄:Yb³⁺/Er³⁺ NR/TiO₂ photoanodes for application in dye-sensitized solar cells (DSSCs). Our investigation focused on how variations in the structure and doping concentration of NaYF₄:Yb³⁺/Er³⁺ NRs within the TiO₂ matrix affected the photovoltaic performance of the DSSCs. Notably, the photoanode that incorporated 1.0 wt% NaYF₄:Yb³⁺/Er³⁺ NRs, annealed at 500 °C, exhibited superior photovoltaic performance, achieving a short-circuit current density (J_sc) of 10.60 mA cm⁻² and a power conversion efficiency (PCE) of 6.20%. This represents a 31.35% increase in J_sc and a remarkable 95.58% improvement in the PCE compared to the reference TiO₂-based DSSC, which had a J_sc of 8.07 mA cm⁻² and a PCE of 3.17%. The enhancements in photovoltaic performance can be attributed to the upconversion properties of NaYF₄:Yb³⁺/Er³⁺ NRs and their ability to facilitate charge separation, which ultimately improves the efficiency of the solar cells.