TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The method after step (iv) either comprises: performing primary evaporation precipitation, where the amount of polycrystalline powder is 0.2 g, vacuum degree is 6.5x 10-3 Pa, the substrate temperature is 300 degrees C and the substrate distance is 15 cm, performing secondary evaporation precipitation, where the amount of polycrystalline powder is 0.1 g, vacuum degree is 6.5-x 10-3 Pa, the substrate temperature is 300 degrees C and the substrate distance is 15 cm, evaporating aluminum film after vacuum evaporating silicon film, where the amount of aluminum powder is 0.1 g, vacuum degree is 5.5x 10-3 Pa, the substrate temperature is 400 degrees C, and the substrate distance is 5 cm, and vacuum annealing at 450 degrees C for 2 hours at a vacuum degree of 5x 10-2 Pa to obtain a film with a thickness of 5.6 mu m, crystalline ratio of 73.2%, and theoretical photoelectric conversion efficiency of 8.3%; or performing primary evaporation precipitation, where the amount of polycrystalline powder is 0.6 g, vacuum degree is 4.5x 10-3 Pa, the substrate temperature is 450 degrees C and the substrate distance is 10 cm, performing secondary evaporation precipitation, where the amount of polycrystalline powder is 0.2 g, vacuum degree is 4.5-x 10-3 Pa, the substrate temperature is 400 degrees C and the substrate distance is 5 cm, evaporating aluminum film after vacuum evaporating silicon film, where the amount of aluminum powder is 0.2 g, vacuum degree is 4.5x 10-3 Pa, the substrate temperature is 400 degrees C, and the substrate distance is 5 cm, and vacuum annealing at 550 degrees C for 3 hours at a vacuum degree of 3x 10-2 Pa to obtain a film with a thickness of 9.7 mu m, crystalline ratio of 89.4%, and theoretical photoelectric conversion efficiency of 10.5%; or performing primary evaporation precipitation, where the amount of polycrystalline powder is 0.4 g, vacuum degree is 7.5x 10-3 Pa, the substrate temperature is 500 degrees C and the substrate distance is 5 cm, performing secondary evaporation precipitation, where the amount of polycrystalline powder is 0.2 g, vacuum degree is 7.5-x 10-3 Pa, the substrate temperature is 500 degrees C and the substrate distance is 5 cm, evaporating aluminum film after vacuum evaporating silicon film, where the amount of aluminum powder is 0.1 g, vacuum degree is 6.5x 10-3 Pa, the substrate temperature is 400 degrees C, and the substrate distance is 5 cm, and vacuum annealing at 650 degrees C for 4 hours at a vacuum degree of 4x 10-2 Pa to obtain a film with a thickness of 8.9 mu m, crystalline ratio of 84.6%, and theoretical photoelectric conversion efficiency of 9.1%; or performing primary evaporation precipitation, where the amount of polycrystalline powder is 0.3 g, vacuum degree is 5.5x 10-3 Pa, the substrate temperature is 350 degrees C and the substrate distance is 10 cm, performing secondary evaporation precipitation, where the amount of polycrystalline powder is 0.1 g, vacuum degree is 5.5-x 10-3 Pa, the substrate temperature is 350 degrees C and the substrate distance is 10 cm, evaporating aluminum film after vacuum evaporating silicon film, where the amount of aluminum powder is 0.3 g, vacuum degree is 7.5x 10-3 Pa, the substrate temperature is 400 degrees C, and the substrate distance is 5 cm, and vacuum annealing at 500 degrees C for 2.5 hours at a vacuum degree of 3x 10-2 Pa to obtain a film with a thickness of 8.2 mu m, crystalline ratio of 84.6%, and theoretical photoelectric conversion efficiency of 9.1%.