NOVELTY - Preparing epitaxial silicon film, comprises adopting hot wire chemical vapor deposition process for the epitaxial growth of silicon thin film on the monocrystalline silicon surface comprising: (a) soaking single surface polished N-type (100) crystal and float-zone (FZ) monocrystalline silicon wafer in aqueous hydrofluoric acid solution and heating in a reaction chamber and; (b) introducing hydrogen and maintaining pressure; (c) depositing an epitaxially grown intrinsic silicon film on the wafer surface; and (d) depositing P-type boron-doped silicon thin film on the film surface.    USE - The epitaxially grown thin film silicon material produced by the method is useful as an emitter of the silicon substrate heterojunction solar battery.    ADVANTAGE - The method can achieve mismatch control of the energy band of the heterojunction battery interface to a low amount so that the conduction band offset and valence band offset are reduced i.e. to reduce the barrier height of the photogenerated carrier, collect the photogenerated carriers more efficiently and greatly improve the doping efficiency of epitaxially grown thin film to improve the electrical conductivity, which is more conducive for the collection of the carrier to improve the short circuit current density and photoelectric conversion efficiency of the battery.    DETAILED DESCRIPTION - Preparing epitaxial silicon film, comprises adopting hot wire chemical vapor deposition process for the epitaxial growth of silicon thin film on the monocrystalline silicon surface comprising: (a) soaking the single surface polished N-type (100) crystal and float-zone (FZ) monocrystalline silicon wafer in aqueous hydrofluoric acid solution (2-3% concentration) for 5-20 seconds, removing oxides from the monocrystalline silicon wafer surface, and then placing in a reaction chamber, vacuumizing, where the vacuum degree is 2x 10-4-9x 10-5 Pa, and heating the substrate to make the silicon wafer surface temperature as 260-400 degrees C; (b) introducing hydrogen into the reaction chamber, where the hydrogen flow rate is 200-300 standard cubic centimeter per minute, regulating the voltage of the two ends of the hot wire to attain 1700-1900 degrees C as the hot wire temperature, maintaining pressure at 180-220 Pa for 40-60 seconds to reduce the silicon wafer surface defect state density and to promote the epitaxial growth of the film; (c) maintaining the hot wire at 1700-1900 degrees C, introducing hydrogen and silane into the reaction chamber, where the hydrogen and silane flow ratio is 49:1, maintaining pressure at 1-3 Pa, and depositing an epitaxially grown intrinsic silicon film of 1-8 nm thickness on the monocrystalline silicon wafer surface to form the interface buffer layer of the silicon substrate heterojunction solar battery; and (d) maintaining the hot wire at 1700-1900 degrees C, introducing hydrogen, silane and trimethylborane into the reaction chamber, where the hydrogen, silane and trimethylborane flow ratio is 9:1:0.002, maintaining pressure at 1-3 Pa, and depositing an epitaxially grown P-type boron-doped silicon thin film of 15-20 nm thickness on the intrinsic epitaxial silicon film surface to form the emitter of the silicon substrate heterojunction solar battery.