NOVELTY - A pi -bridge benzotriazole double-stranded phenothiazine dye (I) is new.    USE - pi -Bridge benzotriazole double-stranded phenothiazine dye used for preparing dye-sensitized solar battery (claimed).    ADVANTAGE - The phenothiazine dye improves absorbing amount, inhibits dye aggregation, has wide absorption spectrum, and improves dye-sensitized solar battery photoelectric conversion efficiency.    DETAILED DESCRIPTION - A pi -bridge benzotriazole double-stranded phenothiazine dye of formula (I) is new.    n=0-5;    X=O or S; and    R=straight-chain or branched-chain 1-20C alkyl, amide, or alkoxy, or halo.    INDEPENDENT CLAIMS are included for:    (1) dye-sensitized solar battery comprising photoanode, photocathode, photoanode substrate, photocathode substrate, and electrolyte, where photoanode substrate and photocathode substrate is a conductive glass substrate, photoanode substrate is set with nanoporous titanium dioxide thin film and compound (I), photoanode substrate is set with catalyst layer of platinum, and nanoporous titanium dioxide thin film is formed in closed cavity filled with electrolyte; and    (2) preparation of dye-sensitized solar battery comprising (A) cleaning fluorine doped tin oxide (FTO) conductive glass in oil agent, anhydrous ethanol and deionized water and drying; (B) mixing 10 ml titanium butoxide and 20 ml ethanol, stirring, adding 18 ml acetic acid and 50 ml deionized water, stirring, vacuum heating at 230 degrees C for 12 hours, naturally cooling to room temperature, filtering, repeatedly washing with deionized water and ethanol, and drying at 50 degrees C for 6 hours; (C) taking 1 g nanocrystalline particles, adding 8 ml ethanol, 0.2 ml acetic acid, 3 g terpineol, and 0.5 g ethyl cellulose, fully grinding for 40 minutes, and ultrasonic treating for 15 minutes; (D) handling conductive glass facing up, placing screen wire on glass at 1 cm distance, adding titanium dioxide nano-crystal slurry, repeatedly baking in oven at 125 degrees C for 5 minutes, 325 degrees C for 5 minutes, 375 degrees C for 5 minutes, 450 degrees C for 15 minutes, and 500 degrees C for 15 minutes until film thickness is 15-17 mu m, dipping in 0.04 M titanium tetrachloride at 70 degrees C for 30 minutes, removing titanium dioxide film, washing with deionized water, heating at 520 degrees C for 30 minutes, cooling to room temperature, placing in desiccator, and storing in sealed bag; (E) dissolving in phenothiazine dye in tetrahydrofuran and methylene dichloride to prepare 5x 10-4 mol/l; (F) mixing ethyl acrylonitrile and methyl acrylonitrile containing 0.6 M 1-methyl-3-propylimidazolium iodide, 0.1 M guanidine thiocyanate, 0.03 M iodine gas, and 0.5 M tert-butyl pyridine to prepare electrolyte solution; (G) dipping sensitized nanoporous photoanode titanium dioxide thin film in dye solution; (H) dissolving chloroplatinic acid in isopropanol, adding to conductive glass surface, uniformly roll coating on surface, drying at 400 degrees C for 15 minutes, thermal decomposing, depositing platinum on conductive glass surface, cooling, cutting, and soaking in anhydrous ethanol; and (I) covering photoanode with photocathode of molybdenum electrode, clipping together, opening to-be tested dye-sensitized solar battery, injecting electrolyte solution to electrode, and sealing.