NOVELTY - High-efficiency solar thin film battery, which is of single multi-laminated p-type layer (P)-intrinsic layer (I)-n-type layer (N) thin film solar battery structure or multiple multi-laminated PIN thin film solar batteries structure, has upper conversion fluorescent material film layer, i.e. sodium yttrium hexafluoride (NaYF6):ytterbium (Yb), erbium (Er), thulium (Tm) material thin film, gadolinium zirconium fluoride (GdZrF7):Yb, Er, Tm material thin film, GdZrF7:Yb, Er thin film, YAl5O3:Yb, Er thin film, yttrium niobium oxide (Y3NbO7):Yb, Er thin film, or ZnAl2O4:Yb, Er thin film.    USE - High-efficiency solar thin film battery i.e. silicon-based thin film solar battery.    ADVANTAGE - The doping amounts of rare earth elements such as Yb, Er, and Tm are adjusted such that the upper conversion fluorescent material can absorb near infrared light in 800-2000 nm wavelength and UV light in 200-350 nm, and emit visible light. The upper conversion fluorescent material film increases energy spectrum absorption range of silicon-based thin film solar battery. Because the silicon-based thin film solar battery has the maximal photoelectric conversion efficiency within visible light range, the upper conversion fluorescent material is capable of improving and increasing the photoelectric conversion efficiency and stability of the silicon-based thin film solar battery.    DETAILED DESCRIPTION - High-efficiency solar thin film battery has upper conversion fluorescent material film layer. It is of:    (1) single multi-laminated PIN thin film solar battery structure comprising first structure, i.e. stainless steel substrate/upper conversion fluorescent material film/transparent conductive oxide (TCO)/n- mu crystalline (c)-silicon (Si)/i-A-silicon carbide (SiC)/i-A-Si/i- mu c-SiC/P'-A-SiC/TCO/antireflecting film; and second structure, i.e. aluminum (Al)/upper conversion fluorescent material film/TCO/n- mu c-Si/i-A-Si1-xGex/i-A-Si/i- mu c-SiC/P'-A-SiC/TCO/glass substrate/antireflecting film; or    (2) multiple multi-laminated PIN thin film solar batteries structure comprising first structure i.e. stainless substrate/upper conversion fluorescent material film/TCO/n- mu c-Si/i- mu c-Si/p- mu c-Si/intermediate reflecting layer/n-A-Si1-xGex/i-A-Si1-xGex/p-A-Si1-xGex/intermediate reflecting layer/n-A-Si/i-A-Si/p-A-Si/intermediate reflecting layer/n- mu c-SiC/i- mu c-SiC/p- mu c-SiC/intermediate reflecting layer/n-A-SiC/i-A-SiC/p-A-SiC/TCO/antireflecting film; and second structure, i.e. Al/upper conversion fluorescent material film/TCO/n- mu c-Si/i- mu c-Si/p- mu c-Si/intermediate reflecting layer/n-A-Si1-xGex/i-A-Si1-xGex/p-A-Si1-xGex/intermediate reflecting layer/n-A-Si/i-A-Si/p-A-Si/intermediate reflecting layer/n- mu c-SiC/i- mu c-SiC/p- mu c-SiC/intermediate reflecting layer/n-A-SiC/i-A-SiC/p-A-SiC/TCO/glass substrate/antireflecting film.    In the third and fourth layers of multiple multi-laminated PIN thin film solar batteries structure, one film layer is provided between the TCO layer and adjacent intermediate reflecting layer or between 2 adjacent intermediate reflecting layers. The upper conversion fluorescent material thin film is NaYF6:Yb, Er, Tm material thin film, GdZrF7:Yb, Er, Tm material thin film, GdZrF7:Yb, Er thin film, YAl5O3:Yb, Er thin film, Y3NbO7:Yb, Er thin film, or ZnAl2O4:Yb, Er thin film.    /=interface between 2 layers;    n=electronic semiconductor;    P'=hole semiconductor;    A=non-crystal;and    x=0-1.    An INDEPENDENT CLAIM is included for preparation of upper conversion fluorescent material NaYF6:Yb, Er, Tm or GdZrF7:Yb, Er, Tm thin film comprising:    (A) preparing NaYF6:Yb, Er, Tm powders or GdZrF7:Yb, Er, Tm powders by (i) liquid phase co-precipitation method or high-temperature thermal reaction method, comprising in a vessel, preparing rare earth trifluorides i.e. Yb tris(trifluoroacetate) (CF3COO)3, Er(CF3COO)3, Tm(CF3COO)3, Na(CF3COO), and Y(CF3COO)3 according to mol ratio of NaYF6:Yb, Er, Tm, or Gd(CF3COO)3, Yb(CF3COO)3, Er(CF3COO)3, Tm(CF3COO)3, and Zr(CF3COO), according to mol ratio of GdZrF7:Yb, Er, Tm; dissolving in a solvent comprising oleic acid and 1-octadecene at 1:1 weight ratio; controlling the weight ratio concentration of the solution at 2-10%; vacuumizing the vessel by filling the vessel with argon gas as protective atmosphere; heating the solution inside the vessel up to 300-330 degrees C at 10-50 degrees C/minute; preserving heat for 1-2 hours; reacting; cooling the reaction solution to room temperature; pouring in n-hexane solvent; stirring, centrifuging, and separating to produce crystallized powders of NaYF6:Yb, Er, Tm, or GdZrF7:Yb, Er, Tm, where volume ratio of the reaction solution to hexane solvent is 1:8-12; washing crystallized powders of NaYF6:Yb, Er, Tm or GdZrF7:Yb, Er, Tm with tetrahydrofuran or butyl ether for 3 times; centrifuging and separating; drying at 110-130 degrees C for 100-140 minutes; and employing high-temperature thermal treatment method and laser crystallization method to treat the dried crystallized powders to further increase crystal size of NaYF6:Yb, Er, Tm or GdZrF7:Yb, Er, Tm to 2-10 mu m; (ii) preparing NaYF6:Yb, Er, Tm powders by first high-temperature thermal reaction method comprising heating raw materials, which are NaF, Y2O3, Yb2O3, Er2O3, Tm2O3, and ammonium fluoride (NH4F) up to 900-1000 degrees C in a sealed quartz glass tube, according to the mol ratio of NaYF6:Yb, Er, Tm; holding the temperature for 1- 2 hours, such that the reaction can be carried out to form crystallized powders of NaYF6:Yb, Er, Tm; or (iii) preparing NaYF6:Yb, Er, Tm powders or GdZrF7:Yb, Er, Tm powders by second high-temperature thermal reaction method comprising heating raw materials, which are NaF, Y2O3, ZrF4, Gd2O3, Yb2O3, Er2O3, Tm2O3, and NH4F up to 800-900 degrees C in a sealed quartz glass tube, according to the mol ratio of NaYF6:Yb, Er, Tm or GdZrF7:Yb, Er, Tm; holding the temperature for 1-2 hours, such that the reaction can be carried out to form crystallized powders of NaYF6:Yb, Er, Tm or GdZrF7:Yb, Er, Tm; and    (B) preparing NaYF6:Yb, Er, Tm or GdZrF7:Yb, Er, Tm thin film comprising pouring NaYF6:Yb, Er, Tm or GdZrF7:Yb, Er, Tm powders into methanol, dimethylbenzene, and/or 2-ethyl hexanoic acid; forming 2-10% suspension; preparing the NaYF6:Yb, Er, Tm or GdZrF7:Yb, Er, Tm thin film from the suspension; depositing NaYF6:Yb, Er, Tm or GdZrF7:Yb, Er, Tm upper conversion fluorescent material thin film by using a suspension film-coating method; drying the resulting thin film; and performing heat treatment at 380-420 degrees C for 1-10 minutes, in hydrogen atmosphere, to form a compact thin film that is 5-30 mu m thick.