NOVELTY - At least one layer of thermoplastic elastomer is sandwiched between a superstrate and a photovoltaic cell. The thermoplastic elastomer comprises at least one silicone ionomer. Thus, photovoltaic device is encapsulated with the thermoplastic elastomer.    USE - Method of encapsulating photovoltaic device (claimed).    ADVANTAGE - The method protects photovoltaic device from environment e.g. wind, rain, snow and dust.    DETAILED DESCRIPTION - At least one layer of thermoplastic elastomer is sandwiched between a superstrate and a photovoltaic cell. The thermoplastic elastomer comprises at least one silicone ionomer. Thus, photovoltaic device is encapsulated with the thermoplastic elastomer. The silicone ionomer is of formula: (XvR3-vSiOl/2)a(XwR2-wSiO2/2)b(XyR1-ySiO3/2)c(SiO4/2)d.    R=monovalent alkyl or aryl;    X=monovalent alkyl, aryl or carboxy functional group of formula: -G-COOZ;    G=divalent spacer group having at least 2 spacing atoms;    Z=H, alkali metal cation, alkaline-earth metal cation, transition metal cation or metal cation;    v=0-3;    w=0-2;    y=0-1;    a,c=more than 0 to less than 0.9;    b=more than 0 to less than 1;    d=more than 0 to less than 0.3;and    a+b+c+d=l.    (i) The average number-of-moles of carboxy functional groups per silicon atom is 0.002 mole or more; (ii) The content of group (Z) of the carboxy functional group is 10 mol% or more. INDEPENDENT CLAIMS are included for the following:    (1) photovoltaic device, which has thermoplastic elastomer disposed on the surface of superstrate and photovoltaic cell disposed on the thermoplastic elastomer;    (2) dissipation of heat, which involves interposing a composition (a) containing the silicone ionomer along a thermal path between a heat source and a heat spreader;    (3) device (A), which consists of an electronic device, an interface material and a heat sink. The interface material is arranged along a thermal path extending from a surface of the electronic component to a surface of the heat sink, and comprises at least one silicone ionomer; and    (4) device (B), which consists of heat spreader and interface material on the surface of heat spreader.