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.

Effect of Interfacial Polarization on the Trap Passivation and Dielectric Constant of SrF2/TiO2 for Dye-Sensitized Solar Cells

“…On the other hand, the high ε′ of a hybrid photoanode material enhances the charge separation and increases the charge carriers in conduction band (CB) TiO 2 , thus lifting the quasi-Fermi level of a SrF 2 /TiO 2 photoanode. 34 It clearly confirms the electron filling in trap states, and this effect will have a stronger influence on the increase in V oc of those devices.…”

“…In addition, the electron diffusion length ( L n ), diffusion coefficient ( D e ), and transport lifetime (τ t ) are important parameters for defining the performance of DSSCs. These were estimated using eqs –, respectively: L n = false( D e τ e false) 1 / 2 D e = L 2 / R ct C μ τ t = R ct C μ where L is the thickness of the photoanode material. The calculated parameters are summarized in Table .…”

Nanocrystals as performance-boosting materials for solar cells

“…Ni-doped Co 3 S 4 and Co 4 S 3 and ternary sulphide NCs of NiCo 2 S 4 and Zn 2 SnO 4 have been used for DSSCs, 171,172 while doped SrSnO 3 NCs for PSCs. 173 NCs have been used as IFL for NC-LHSCs, 49,141,174–179 OSCs, 180–185 DSSCs, 186–195 PSCs, 196–212 and Si solar cells. 213–220 FAPbBr 3 perovskite NCs have been used as a multifunctional luminescent-downshifting passivation layer for GaAs solar cells.…”

“…11,14,15,17–22 Additionally, perovskite NCs are also good alternatives for light harvesting in solar cells. 12–14,16,23–28 Besides active layers (light harvesting layers), functional layers based on NCs, mainly including hole transport layers (HTLs), 29–99 electron transport layers (ETLs) 100–173 and interfacial functional layers (IFLs), 174–221 are of great importance in solar cells. Notably, NC additives also boost the performance of solar cells through defect passivation, plasmonic effect, solar concentration, light up-conversion and down-conversion/shifting, light scattering and reflection, and heat sinks.…”

A Review on the Applicability of Luminescent Phosphors and Effective Positioning in Dye‐Sensitized Solar Cells for Enhanced Performance and Stability

“…Recently, the cubic SrF 2 :Pr 3+ Yb 3+ DC nanophosphors which could spectrally convert the near UV‐light photons (≈440 nm) to visible light photons (green and red) have been demonstrated for DSSCs under indoor‐light applications. [ 43 ] The nanophosphors were utilized in‐between the bl‐TiO 2 and mp‐TiO 2 layer of the DSSCs for spectral tuning and they achieved PCE of 9.1% as compared with the control cells without the DC layer (8.4%). They reached a maximum PCE of 15.9% under low‐intensity indoor light conditions and it was the first report on phosphors used for efficiency enhancement under indoor light condition.…”