Optical Materials 121 (2021) 111646 Available online 5 October 2021 0925-3467/Published by Elsevier B.V. Research Article Novel Down-converting single-phased white light Pr 3+ doped BaWO 4 Nanophosphors material for DSSC applications R. Kamal a, * , H. Hafez b a Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, 11711, Cairo, Egypt b Nano-Photochemistry and Its Environmental Applications Laboratory, Environmental Studies and Research Institute (ESRI), University of Sadat City, Sadat City, 23897, Menofa, Egypt A R T I C L E INFO Keywords: DSSC Down-conversion Pr 3+ doped BaWO 4 Nanophosphors ABSTRACT White Nanophosphors based on praseodymium doped barium tungstate matrix (y mol Pr 3+ : BaWO 4 (PBWO) (y = 0.01, 0.03, 0.05, 0.07 mol) were synthesized by ultrasound assisted hydrothermal method in the presence of citric acid and characterized as novel down-conversion materials for dye-sensitized solar cells (DSSCs) appli- cations. The different prepared PBWO Nanophosphors show high crystalline tetragonal phase with nano-cubic morphology. The PBWO photoluminescence spectra give strong emission peaks at 486, 529, 615, 623 and 643 nm are corresponding to the 3 P 0 → 3 H 4 , 3 P 1 → 3 H 5 , 1 D 2 → 3 H 4 , 3 P 0 → 3 H 6 and 3 P 0 → 3 F 2 transitions of Pr 3+ , respectively. These photoluminescence spectra are assigned to blue, green and red-light regions which cover the whole visible light region. It means that these Nanophosphor materials are promising materials for down- conversion applications. By varying the Pr 3+ ion conc., it was found that the optimum conc. of Pr 3+ ion was 0.05 mol which gives the highest photoluminescence intensity. The prepared Nanophosphors were applied in DSSCs as a top down-converting layer on the photoactive TiO 2 electrode. A high conversion effciency (η) of 8.08% was achieved by the application of top (PBWO: 0.05 mol Pr 3+ ) down-converting material compared with a 4.17% effciency of the non-modifed DSSC. This enhancement is probably due to the improved UV radiation harvesting via a down-conversion luminescence process. 1. Introduction In recent decades, dye sensitized solar cells (DSSCs) are considered one of photovoltaic technologies which attracted the attention due to its low cost, high stability, easy of processing, high conversion effciencies (PCEs) and belongs to next generation photovoltaic cells as a kind of green energy source [1–4]. Typically, DSSCs are composed of a photo- electrode, a counter electrode and a redox electrolyte containing iodide and tri-iodide ions [5,6]. Photoelectrode plays an important role in generation of photo-excited electrons in the performance of DSSC. In 1991 [7], the frst studies on DSSCs with conversion effciency of 7% by O’regan and Gratzel based on visible light sensitizing material with TiO 2 nanoparticles. Several methods for modifying of effciency of photo- electrode include surface modifcation, surface treatment, semi- conductor recombination, luminescent materials, and structural optimization [8–12]. As the photoelectrode light absorption spectrum can strongly affect the amount of light energy absorbed by the DSSC [13]. Recently, In DSSCs using conversion luminescent materials is a perfect choice to extend light absorption, which can shift or convert a broad spectrum of light into photons of a specifc wavelength [14]. The luminescence mechanisms of up-conversion (UC), down-conversion (DC) or down shifting (DS) can be used to convert the infrared or ul- traviolet light into visible light [15]. Down-shifting is a single photon procedure that includes conversion of one absorbed photon at high en- ergy into one photon with low energy. This process confrms to the Stokes Law with wavelength change known as Stoke’s shift. Down-converting materials can convert one high energy photon into one or more photons with low energy. Both processes can decrease the loss of energy result from thermalization of hot charge carriers after the ab- sorption of photons with high energy [16,17]. Among Down converting materials, rare earth (RE) ions have been used successfully in dye sensitized solar cells for improving the light scattering and absorption spectrum of dye-loaded photoactive electrodes in DSSCs [18]. There- fore, down converting materials can play an important role in the eff- ciency enhancement of DSSCs [14,19]. Praseodymium (Pr 3+ ) doped * Corresponding author. E-mail address: raghdakamal@edu.asu.edu.eg (R. Kamal). Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat https://doi.org/10.1016/j.optmat.2021.111646 Received 7 June 2021; Received in revised form 14 September 2021; Accepted 28 September 2021