NOVELTY - Solar cell protective sheet comprises a polymer substrate and a polymer layer provided on the polymer substrate, where: the polymer substrate is a surface-treated polymer substrate, and the polymer layer has a thickness of 0.8-12 mu m and contains a composite polymer containing a polysiloxane structural unit (I) and a non-polysiloxane structural unit in the molecule; or the sheet contains a first polymer layer containing an UV absorbent and a binder polymer on the polymer substrate, and a second polymer layer provided on the first polymer layer and containing a binder polymer.    USE - The solar cell protective sheet is useful as backsheet in solar cell module (all claimed).    ADVANTAGE - The solar cell protective sheet: exhibits a ratio of elongation at break of at least 50%, after stored under the conditions of 120 degrees C and 100% relative humidity for 50 hours, to the elongation at breaking before storage; a thermal shrinkage of -1% to 1% in heat treatment at 150 degrees C for 30 minutes; exhibits excellent adhesiveness durability in wet heat environments; can be produced in an economical manner; and provides the solar cell module that exhibits good power generation performance and secures long-term stable power generation efficiency in wet heat environments.    DETAILED DESCRIPTION - Solar cell protective sheet comprises a polymer substrate and at least one polymer layer provided on the polymer substrate, where: the polymer substrate is a surface-treated polymer substrate, and the polymer layer has a thickness of 0.8-12 mu m and contains a composite polymer containing a polysiloxane structural unit of formula (-(-Si(R1)(R2)-O-)n-) (I) and a non-polysiloxane structural unit in the molecule; or the sheet contains a first polymer layer containing an UV absorbent and a binder polymer on the polymer substrate, and a second polymer layer provided on the first polymer layer and containing a binder polymer, in which the content of the UV absorbent is at most 1 mass% relative to the total amount of the binder.    R1, R2 = H, halo, or a monovalent organic group, preferably alkyl, aryl, aralkyl, alkoxy, aryloxy, mercapto, amino or amide; and    n = greater than or equal to 1.    INDEPENDENT CLAIMS are also included for:    (1) a backsheet for solar cells, containing the solar cell protective sheet;    (2) producing the solar cell protective sheet, comprising surface-treating at least one surface of the polymer substrate (16), and applying a coating liquid containing a composite polymer onto the surface-treated surface of the polymer substrate so that the thickness after drying could be 0.8-12 mu m; and    (3) a solar cell module (10) containing at least one solar cell protective sheet.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross-sectional view of the solar cell module.    Solar cell backsheet (5)    Solar cell module (10)    Polymer substrate (16)    Sealant (22)    Transparent substrate (24)