NOVELTY - Poly(N-alkyl-4-ethylene pyridine)iodide solid polymer electrolyte comprises conductive polymer matrix poly(N-alkyl-4-ethylene pyridine)iodide, additive N-alkyl pyridine iodine salt and conductivity reinforcing agent iodine in the mol ratio of 1: 0.3-3: 0.5-4. The alkyl in poly(N-alkyl-4-ethylene pyridine)iodide and N-alkyl pyridine iodine salt is 1-4 carbon alkyl.    USE - Poly(N-alkyl-ethylene pyridine)iodide solid polymer electrolyte for use dye sensitized nano-crystalline solar cell (Claimed), and also for use in fields, such as window materials, solid secondary cell, electroluminescence, electrochromism and sensor.    ADVANTAGE - The poly(N-alkyl-4-ethylene pyridine)iodide solid polymer electrolyte shows higher conductivity 3-5 millisiemens per centimeter and 5.64% photoelectric conversion efficiency.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for preparing poly(N-alkyl-4-ethylene pyridine)iodide solid polymer electrolyte, which involves :    (A) dissolving 4-ethylene pyridine and azo-bis-iso-butyrynitrile in aromatic inert solvent and reacting for 8-15 hours at 70-80 degrees C under protection of nitrogen for preparing poly(4-ethylene pyridine)polymer matrix;    (B) dissolving prepared poly(4-ethylene pyridine) in alcohol solvent and adding iodoalkane for reacting for 8-15 hors at 60-80 degrees C under protection of nitrogen for preparing poly(N-alkyl-4-ethylene pyridine)iodide;    (C) adding pyridine and iodoalkane to cyclohexane and carrying out reflux reaction for 15-30 hours at 60-70 degrees C under the protection of nitrogen for preparing N-alkyl pyridine iodine salt;    (D) adding prepared poly(N-alkyl-4-ethylene pyridine)iodide and N-alkyl pyridine iodine salt, and iodine to alcohol solvent and carrying out reflux reaction for 8-15 hours at 60-80 degrees C under protection of nitrogen for preparing solid electrolyte solution; and    (E) coating solid electrolyte solution to matrix, drying in vacuum to prepare solid electrolyte.