Rare Earth Materials Applied For Dye Sensitized Solar Cells

Dye sensitized solar cells (DSSCs) have been developed rapidly in recent yearsbecause of their advantages of lower energy consumption, lower cost, easierpreparation and better flexibility. However, the power conversion efficiency is stillvery low contrast to traditional silicon solar cells, which limits the application of theDSSCs largely. The fundamental reason for the low efficiency of DSSCs is themismatch between the spectral response range of DSSCs and the solar spectrum. Asthe core part of the DSSCs, the absorption range of the dye is generally shorter than750nm. However,55%-60%of the solar spectrum distributes in the near infrared(NIR) region, so the fundamental method to improve the efficiency of DSSCs isexpanding the spectral response range. There are two effective methods to expand thespectral response range of DSSCs which is converting NIR to visible light usingupconversion (UC) luminescence materials and developing new NIR dye. Even theemission peaks of β-phase NaYF4:Yb3+, Er3+which has the highest UC efficiencycannot match with the absorption of regular dye molecules for its4f–4f sharp linesemission of trivalent rare earth ions. So the study on broadband UC luminescencematerials is very necessary. The energy level of the dye molecules in DSSCs mustmatch with semiconductor, so considering the new synthetic NIR dye in the future,the study on the new semiconductor using for DSSCs has the potential value.Therefore, focus on the study of new UC luminescence materials and newsemiconductor suitable for DSSCs; we carry out the study as follow:(1) We have systematically studied the super-intense white UC emission ofYb2O3polycrystals. Using a980nm laser diode as laser source, we have studied thechanges of emission spectra of both Yb2O3and β-NaYF4:Yb3+, Er3+for contrast underdifferent power density excitation. We found that Yb2O3shows a super-intense whiteUC emission under high power density excitation, which is much stronger thanβ-NaYF4:Yb3+, Er3+under the same conditions. We also found that the source of thesuper-intense white UC emission of Yb2O3is not come from blackbody radiation through the study of the sample temperature. Then we present a new white UCemission model of Yb2O3which is the electron-hole recombination mechanism.Finally, we studied the I-V characteristics of the DSSCs employ Yb2O3andβ-NaYF4:Yb3+, Er3+as UC converter under980nm excitation respectively. It is foundthat the efficiency increasing rate of Yb2O3-DSSCs is higher than NaYF4-DSSCs withthe increasing laser power density. The efficiency of Yb2O3-DSSCs is nearly2.4timeslarger than NaYF4-DSSCs when the laser power density is as high as4.737W/mm2.(2) The study on semiconductor In2O3has potential application value for DSSCs,because its energy level can probably match with NIR dye in the future. We haveprepared In2O3one-dimensional nanotubes by the electrospinning method, andapplied to DSSCs as anode semiconductor materials. The DSSCs based on In2O3nanotubes shown improved performance for the excellent electronic transmissioncharacteristics of one-dimensional structure compared with the previous report.Furthermore, we study the effect of DSSCs doping with rare earth ions into In2O3nanotubes respectively, and its efficiency significant improved. In order to investigatethe electron transfer process in the In2O3:RE3+-DSSCs, electrochemical impedancespectroscopy (EIS) measurements were performed, and the reduction ofrecombination of electrons in In2O3-DSSC by doping with rare earth ions was found,which is the reason of the improvement of the In2O3-DSSC. With Er3+doping,efficiency of In2O3-DSSCs increased to1.447%which is the highest efficiency ofDSSCs based on In2O3.