TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Components: The solar cell module comprises: a transparent front substrate (24) on the sunlight incident side of it; a cell side substrate on which the solar cell element is encapsulated with a sealant; and a solar cell backsheet (5) so arranged on the cell side substrate as to be opposite to the front substrate and to be in contact with the sealant (22), and comprising the solar cell protective sheet as the solar cell backsheet.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The surface treatment applied to the polymer substrate is at least one of flame treatment, low-pressure plasma treatment, atmospheric pressure plasma treatment (preferred) or UV treatment. (I) is present at 15-85 mass% of the entire composite polymer molecule. The non-polysiloxane structural unit is at least one of a vinyl-type structural unit, a polyester-type structural unit or a polyurethane-type structural unit. The polymer layer containing the composite polymer: has a crosslinked structure; and is provided in contact with the surface of the surface-treated polymer substrate, or is an outermost layer so arranged as not to be in contact with the surface of the polymer substrate. The polymer substrate contains a polyester-type resin, and the carboxy group content of the polyester resin is 2-35 equivalent/t. The polymer substrate is a polyester. The second polymer layer contains at least one of a fluoropolymer or a silicone polymer as the binder polymer. The first polymer layer contains at least one of a silicone polymer, a polyester polymer or a polyurethane polymer as the binder polymer. In the solar cell protective sheet, at least one of the first polymer layer and the second polymer layer further contains a crosslinking agent (0.5-50 mass%, relative to the binder polymer); and at least one polymer layer is a light-reflective layer containing a white pigment. The crosslinking agent is a carbodiimide-type crosslinking agent or an oxazoline-type crosslinking agent. The first polymer layer further contains inorganic fine particles (0.5-50 vol.%). The ratio of the thickness (L1) of the second polymer layer to the thickness (L1) of the first polymer layer (L2/L1) is 0.13/1-24/1. The composite polymer-containing coating liquid further contains a solvent, where at least 50 mass% of the solvent is water; and a crosslinking agent. EXAMPLE - Propylene glycol mono-n-propyl ether (PNP) (81 parts), isopropyl alcohol (360 parts), phenyltrimethoxysilane (110 parts) and dimethyldimethoxysilane (71 parts) were fed into a reactor equipped with a stirrer and a dropping funnel and purged with nitrogen gas, and heated up to 80 degrees C with stirring in a nitrogen gas atmosphere. Then a mixture of methyl methacrylate (260 parts), n-butyl methacrylate (200 parts), n-butyl acrylate (110 parts), acrylic acid (30 parts), 3-methacryloyloxypropyltrimethoxysilane (19 parts), tert-butyl peroxy-2-ethylhexanoate (31.5 parts) and PNP (31.5 parts) was dropwise added to the reactor at the same temperature, for 4 hours. Subsequently, this was stirred under heat at the same temperature for 2.5 hours to give a solution of an acrylic polymer having a carboxy group and a hydrolyzable silyl group and having a weight-average molecular weight of 29300. Then deionized water (54.8 parts) was added, and continuously stirred under heat for 16 hours to hydrolyze the alkoxysilane, and was further condensed with the acrylic polymer to give a solution of a composite polymer. Then triethylamine (42 parts) was added to the solution with stirring at the same temperature, and stirred for 10 minutes. Subsequently, deionized water (1250 parts) was dropwise added at the same temperature for phase conversion emulsification, for 1.5 hours, and then heated up to 50 degrees C and stirred for 30 minutes. Then a part of water was removed under reduced pressure along with the organic solvent at an internal temperature of 40 degrees C, to obtain a composite polymer aqueous dispersion. Slurry of high-purity terephthalic acid (100 kg) and ethylene glycol (45 kg) was sequentially fed into an esterification tank previously charged with bis(hydroxyethyl)terephthalate (123 kg) and kept at 250 degrees C and a pressure of 1.2x 105 Pa. The mixture was further esterified for 1 hour, to obtain an esterification product, which was then transferred into a polycondensation tank. Subsequently, ethylene glycol (0.3 mass%) was added to the polycondensation tank. The mixture was stirred for 5 minutes, an ethylene glycol solution of cobalt acetate and manganese acetate was added at an amount of 30 ppm and 15 ppm, respectively. Further, this was stirred for 5 minutes, and then an ethylene glycol solution of 2 mass% of a titanium alkoxide compound (5 ppm) was added. After 5 minutes, an ethylene glycol solution of 10 mass% of ethyl diethylphosphonoacetate (5 ppm) was added. Next, with stirring the lower polymer at 30 rpm, the reaction system was gradually heated from 250 degrees C to up to 285 degrees C and the pressure was lowered to 40 Pa. The time to the final temperature and that to the final pressure were both 60 minutes. At the time when the stirring torque reached a predetermined level, the reaction system was purged with nitrogen, its pressure was restored to normal pressure and the polycondensation reaction was stopped. Then the obtained product was jetted out into cold water, and immediately cut into polymer pellets. The pellets were melted at 280 degrees C and cast onto a metal drum to form an unstretched film. Subsequently, the film was stretched in the machine direction by 3 times at 90 degrees C and further in the cross direction by 3.3 times at 120 degrees C, to obtain a filmy polymer substrate of a biaxially-stretched polyethylene terephthalate (PET) with a carboxy group content of 30 equivalent/t. The PET was plasma-treated at atmospheric pressure on both sides by irradiating with plasma for 15 seconds at a plasma intensity of 250 W-minute/m2, as generated by a high-frequency discharge apparatus having a power source frequency of 5 kHz in a plasma gas atmosphere of an air/argon gas mixture, while conveyed through the apparatus. Then back layer coating liquid (composed of composite polymer aqueous dispersion (45.9 parts), Epocross WS-700 (RTM: Oxazoline compound) (7.7 parts), polyoxyalkylene alkyl ether (2 parts) and distilled water (44.4 parts)) was applied onto the surface-treated PET and dried at 180 degrees C for 1 minute, to obtain the backsheet i.e. the solar cell protective sheet.