Comparativeanalysisofupconversionefficiencies in fluoride materials for photovoltaicapplication

Infraredtovisibleupconversion(UC)isapromisingwaytoenhancetheefficiency ofsiliconbasedsolar cells. Inthispaper,thespectralconversionandrecoveryofsub-bandgapphotonsofthesolarspectrum, from NIR-IRtotheVIS-NIRwavelengthregion,isinvestigatedintwo fluorides hostsdopedwithtrivalent erbium ions(Er3þ). Theefficiency gainduetoupconversioninsiliconsolarcellsiscomparedforsingle crystal samplesofBaY2F8:Er3þ and LiYF4:Er3þ in adedicatedupconvertersolarcelldevice(UCSCD)with monochromatic excitationinthe1.5 mm spectralregion. The highestexternalquantumefficiency duetoupconversionwasfoundfortheUCSCDusingthe BaY2F8:30 at%Er3þ single crystal,reachinganEQEof6.870.2% for(1.1070.12) 105Wm2 spectral irradiance at1494nm. Wepresentacomprehensivespectroscopicstudyofthecrystalsamplesalsotakingintoaccountthe effects ofthedifferentcrystalsymmetryaswellasthedifferentphononenergies.Our findings enableus to explainthehigherefficiency oftheBaY2F8:Er3þ compared totheLiYF4:Er3þ upconverterintermsof both staticanddynamicpropertie