A solar cell module comprises a solar cell layer and an ionomer sheet. The ionomer sheet comprises a first ionomer that is the neutralized product of a first precursor acid copolymer, which, in turn, comprises copolymerized units of ethylene and about 20 to about 30 wt % of copolymerized acrylic or methacrylic acid. The first precursor acid copolymer has a melt flow rate of about 70 to about 1000 g/10 min. When neutralized to a level of about 40% to about 90% and when comprising counterions that consist essentially of sodium cations, the first precursor acid copolymer produces a sodium ionomer that has a melt flow rate of about 0.7 to about 25 g/10 min and a freeze enthalpy that is not detectable or that is less than about 3.0 j/g. The ionomer sheet may further comprise a second ionomer that is different from the first ionomer.