NOVELTY - A back sheet (S1) comprises a polymer base material; and a polymer layer that is provided on the polymer base material and contains a composite polymer that contains, in a molecule, siloxane structural units (15-85 mass.%) and non-siloxane structural units (85-15 mass.%).    USE - As back sheet for a solar cell to be disposed in contact with sealing material of cell-side substrate in which solar cell device is sealed with sealing material; and in solar cell module (claimed).    ADVANTAGE - The back sheet is excellent in the adhesion durability between various layers and the adhesion durability to the constituent base material of the back sheet or a cell-side substrate (e.g. a sealing material such as ethylene vinyl acetate) in a hot and humid environment; can be produced at low cost; and provides an inexpensive solar cell module having stable power generation efficiency.    DETAILED DESCRIPTION - A back sheet (S1) comprises a polymer base material; and a polymer layer that is provided on the polymer base material and contains a composite polymer (R1) that contains, in a molecule, siloxane structural units of formula -(Si(R1)(R2)-O)n- (I) (15-85 mass.%) and non-siloxane structural units (85-15 mass.%).    R1 and R2=H, halo or monovalent organic group;    n=at least 1.    INDEPENDENT CLAIMS are included for the following:    (1) producing (M1) the back sheet (S1) involving forming at least one polymer layer by applying a coating liquid containing the composite polymer (R1) on a polymer base material; and    (2) a solar cell module either comprising the back sheet (S1) or the back sheet produced by the method (M1); or a transparent front substrate through which sunlight enters, a cell structural portion which is provided on the front substrate and comprises a solar cell device and a sealing material that seals the solar cell device, and the back sheet (S1) or the back sheet produced by the method (M1), provided on a side of the cell structural portion opposite to a side of it on which the front substrate is provided, so as to be adjacent to the sealing material.