The main heat aging resistance of PET film is 120 ℃, 100% RH hydrolysis resistance test method. The time for cracking and embrittlement of PET film shall not be less than 96h. The longitudinal shrinkage of PET film can generally be controlled below 1.5% (150 ℃, 30 min). Since the solar photovoltaic cells need to undergo three times of high temperature treatment, the substrate of the battery backplane must have excellent dimensional stability. PET film shall have good tear resistance and toughness to avoid tearing and embrittlement during component processing and outdoor wet, hot, dry and cold environments. As a new energy, solar photovoltaic system is widely used, mainly in space spacecraft, communication systems, microwave relay stations, television differential turntables, photovoltaic water pumps, industrial and agricultural power generation, regional power supply, traffic signs, civil lighting, etc.