Trap‐Assisted Transition Energy Levels of SrF2:Pr3+−Yb3+ Nanophosphor in TiO2 Photoanode for Luminescence Tuning in Dye‐Sensitized Photovoltaic Cells

Abstract

Luminescent nanophosphors as spectral converters offer immense potential for dye‐sensitized photovoltaics (DSPV) to harvest a wide range of the solar spectrum. Herein, a novel structural design of DSPV using a downconversion (dc) nanophosphor layer in the TiO2 photoanode for both indoor (ambient) and outdoor applications is demonstrated. Cubic SrF2:Pr3+−Yb3+ nanoparticles are synthesized by a template‐free hydrothermal technique. The dc nanophosphor absorbs photons of the blue region, leading to emission of a broad luminescence band (green and red), which is well matched with N719‐dye absorption. The mixed‐valence state of Pr ions (Pr3+ and Pr4+) leads to trap‐assisted transition levels, which result in a broad visible emission. For the first time, a unique Pr3+−Yb3+ codoped dc system yielding tuned and intensified luminescence by effective crossrelaxation (CR) with a back energy transfer (BET) mechanism is designed and efficient working of the dc nanophosphor‐layered DSPVs under both outdoor 1 sun (AM 1.5 G) and indoor light (Warm‐3200 K; Day‐5000 K) conditions is demonstrated. Improved efficiency of 9.07% is attained in dc‐dye‐sensitized solar cells (DSSC) compared with a control‐DSSC (8.39%) at 1 sun intensity. Under indoor low‐light conditions (1000 lux), the dc‐DSPV achieves high power conversion efficiencies (PCEs) of 14.85 and 15.9%, respectively. This approach results in a 63.44% increment in output power density for dc‐DSPV compared with the control‐DSPV under LED 3200 K irradiation. These findings suggest that this configuration of dc‐layered DSPV can provide a new strategy for future indoor electronic operations under ambient light conditions.