Electrophoretically Deposited Y2O3:Bi3+,Yb3+ Nanosheet Films as Spectral Converters for Crystalline Silicon Solar Devices

High Resolution Image Download MS PowerPoint Slide Transparent Y 2 O 3:Bi 3+,Yb 3+ films that exhibit near-infrared (NIR) emission under near-ultraviolet (NUV) excitation are candidates for the spectral converters in crystalline silicon solar devices. In this work, NIR-emitting films were fabricated by the aqueous electrophoretic deposition of Y 2 O 3:Bi 3+,Yb 3+ nanosheets, and their photoluminescence (PL) properties were enhanced by a postcalcination process. Positively charged Y 2 O 3:Bi 3+,Yb 3+ nanosheets with adsorbed polyethylenimine (PEI) were deposited as a uniform and dense micrometer thick layer on a transparent conductive substrate by applying an electric field to an aqueous nanosheet dispersion. The resulting nanosheet film showed NIR emission from Yb 3+, realized through energy transfer from Bi 3+, when excited under NUV light. The NIR PL intensity of the film was improved by calcination at 700–1000 °C under a flow of air. This NIR PL enhancement was explained by the calcination process increasing the crystallinity of the Y 2 O 3:Bi 3+,Yb 3+ nanosheets and removing adsorbed hydroxyl groups that quenched the NIR emission of Yb 3+ . Furthermore, the increased energy transfer efficiency of the Bi 3+ → Yb 3+ transition with increasing calcination temperature also contributed to the observed NIR PL enhancement of the nanosheet film. The NIR PL intensity of the as-deposited nanosheet film did not change under continuous NUV excitation, whereas a gradual increase in the PL intensity was observed for the calcined nanosheet films. This increase in the PL intensity of the calcined films would be caused by the photooxidation of the Bi and Yb ions, which were partially reduced by PEI during the calcination process.