A lanthanide-doped inorganic down-shifting nanophosphor that converts the intense ultra-violet (UV) light photons to visible-light photons is highly attractive for dye-sensitized solar cells (DSSCs) to enhance light harvesting and power conversion efficiencies. In the present research, for the first time, a highly luminescent Ce3+-doped SrF2 (Ce3+:SrF2) nanophosphor is employed as a down-shifting nanophosphor material in the photoanode of DSSC. The nanophosphor was synthesized by co-precipitation technique, followed by a rapid microwave calcination approach. The structural and morphological properties of the synthesized nanophosphor are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy analyses. The optical absorption and emission characteristics of the Ce3+:SrF2 down-shifting nanophosphor are investigated. Interestingly, the nanophosphor displayed a broad luminescence in the visible region under UV wavelength excitation. Absorption studies show that the Ce3+:SrF2 nanophosphor absorbs the deep-UV and near-UV radiations, protecting the iodide electrolyte from thermal degradation. To further study the performance of the down-shifting layer in DSSC, the Ce3+:SrF2/TiO2 nanocomposite-based photoanodes were used to fabricate the DSSCs. As a result, the nanocomposite-based device has demonstrated an excellent photo-conversion efficiency of 8.8%. The improvement in the incident-photon-to-current efficiency curve and electrochemical values (J sc = 15.2 mA cm–2, V oc = 0.82 V, and FF = 0.73) are due to the enhanced visible-light photon harvesting and high chemical stability.

Light induced changes in the optoelectronic properties affect the performance and the stability of halide perovskites. In this work, we report the real-time visualization of the photobrightening (PLB) effect using confocal laser scanning microscopy wherein the photon induced enhancement in photoluminescence is observed and their role in conductivity and photovoltaic properties are studied. The methodology is inspired from the Fluorescence Recovery After Photobleaching (FRAP) technique that is traditionally used to study biological cells. The role of composition, and surface/grain boundaries of perovskites, wavelengths, and intensity of illuminating photons, and time of illumination on the photobrightening or photobleaching is thoroughly investigated. The CH 3 NH 3 PbI 3 exhibits a dominant photobrightening effect, with green photons showing more PLB than blue or red photons. The study of PLB between films and single crystals clearly shows the effect is a surface phenomenon. The presence of mixed iodide/bromide or pure bromide in the halide site and formamidinium or cesium in the A site suppressed the PLB. The strain relaxation in the organic site is found to be responsible for the PLB effect, and it enhanced the overall conductivity in material leading to better photovoltaic performance.