Enhancing The Efficiency Of Dyesensitized Solar Cells Through Broadband Near Infrared Upconverting NaYF₄:Yb³⁺,Er³⁺ Nanocrystals

Dye-sensitized solar cells?DSSCs?have been deemed as one of promising alternative to silicon solar cells due to their advantages of lower product costing,being environmental friendly,and being easily fabricated.Despite recent significant development of DSSCs,DSSCs still can not compete with silicon solar cells because of their conversion efficiency,which are strongly limited by the spectral mismatch between the incident solar spectrum and the absorption spectra of light-harvesting dye molecules?300-800 nm?in DSSC devices,resulting in the transparency losses in the infrared range.Upconversion technology,which can convert near infrared light into visible light,has been considered as one of promising solutions to harvest near infrared light for DSSCs.However,the weak and narrowband absorption of lanthanide ions in upconversion materials has posted a stringent limitation for efficient near infrared light harvesting,thus restricting its application in DSSCs.In this thesis,we aimed to develop and employ broad band upconversion materials for uses in DSSCs,and the research contents are described as follows:?1?Upconversion nanoparticles of NaYF₄:Yb³⁺30%,Er³⁺2% were synthesized and applied into DSSCs.The effects of the oleic acid quantity during the particle synthesis,and the depositing time –the immersion time of the photoanode into the hexane solution consisting of NaYF₄:Yb³⁺30%,Er³⁺2% upconversion nanoparticles were systematically studied and optimized.?2?A set of infrared-harvesting dyes?IR-783,IR-806,and IR-820?were then introduced to sensitize the core upconversion nanoparticles of NaYF₄:Yb³⁺30%,Er³⁺2%,enabling broad band upconversion of near infrared light.Under light excitation of 808 nm,the integrated upconverting intensity of nanoparticles increased first and then dropped,when different amounts of dyes were introduced to the surface of upconversion nanoparticles.The comparison results indicated that upconversion nanoparticles sensitized by IR-783 dye had the strongest upconverting luminescence.When the upconversion nanoparticles sensitized dye IR-783,dye IR-806 and dye IR-820 were applied to DSSCs,the cell with upconversion nanoparticles sensitized dye IR-783 exhibited the highest performance improvement,and the enhancement of the efficiency reached about 22.79%.?3?The core-shell structure NaYF₄:Yb³⁺30%,Er³⁺2%@NaYF₄:Yb³⁺20%,Nd³⁺30% nanoparticles were synthesized and then sensitized by the dye IR-783.Under the optimum dye sensitized concentration,the upconverting luminescence intensity of the core-shell structure was determined to be about 10.7 times higher than that of the IR-783-sensitized core nanoparticles NaYF₄:Yb³⁺30%,Er³⁺2%.Approximately 33.63% enhancement of an overall DSSC efficiency was obtained when applying IR-783 dye sensitized core-shell structure nanoparticles into a DSSC.