Enhancement of dye sensitized solar cell efficiency via incorporation of upconverting phosphor nanoparticles as spectral converters

Abstract Upconverting NaYF 4 :Yb 3+ ,Er 3+ / NaYF 4 core‐shell ( CS ) nanoparticles ( NPs ) were synthesized by thermal decomposition of lanthanide trifluoroacetate precursors and mixed with TiO 2 NPs to fabricate dye‐sensitized solar cells ( DSSCs ). The CS geometry effectively prevents the capture of electrons because of the surface states and improves photo‐emission. The as‐synthesized CS NPs show upconversion ( UC ) luminescence, converting near infrared (NIR) light into visible light (450–700 nm), making the photon absorption by the ruthenium‐based dyes (which have little or no absorption in the NIR region) possible. The champion DSSCs fabricated using CS UC NPs (average size = 25 nm) show enhancements of ~12.5% (sensitized with black/ N749 dye) and of ~5.5% (sensitized with N719 dye) in overall power conversion efficiency under AM 1. 5G illumination. This variation in the enhancement of the DSSC efficiencies for black and N719 dyes is attributed to the difference in the extinction coefficient and the absorption wavelength range of dyes. Incident photon‐to‐current conversion efficiency measurements also evidently showed the photocurrent enhancement in the NIR region of the spectrum because of the UC effect. The results prove that the augmentation in efficiency is primarily due to NIR to visible spectrum modification by the fluorescent UC NPs . Copyright © 2015 John Wiley & Sons, Ltd.