NOVELTY - Photovoltaic module (M1) (100) comprises: (a) a front cover (210) and a back cover (240); (b) many photovoltaic cells between the front and back covers; and (c) an interlayer (L) (235) between the photovoltaic cells and the back cover, where the interlayer (L) comprises a base material and a filler material disposed within the base material. The concentration of the filler material disposed within the base material of a first portion of the interlayer (L) is different from the concentration of the filler material disposed within the base material of a second portion of the interlayer (L).    USE - Used as photovoltaic module.    ADVANTAGE - The photovoltaic module: utilizes the interlayer that serves as a moisture barrier between the back cover and the photoelectrically active layers, thus preventing moisture-induced corrosion from occurring inside the module and increasing the module's life expectancy; and exhibits improved performance, durability, affordability, appearance or safety.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a multilayered interlayer (L1) for the photovoltaic module, comprising: (a) and (b) as above per se; a first layer between the photovoltaic cells and the back cover, where the first layer comprises a first base material and a first filler material disposed within the first base material at a first concentration; and a second layer adjacent to the first layer;    (2) a photovoltaic module (M2) comprising a multilayer interlayer (L2) comprising a base material and a filler material disposed within the base material, where: the interlayer (L2) further comprises a first layer (having a first concentration of filler material, a first side and a second side), a second layer arranged on the first side of the first layer and having a second concentration of filler material, and a third layer arranged on the second side of the first layer having a third concentration of filler material; and the first concentration is different than the second and third concentrations; and    (3) a photovoltaic module (M3) comprising the interlayer (L).    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional side view of the photovoltaic module.    Photovoltaic module (100)    Front cover (210)    Front contact layer (215)    Interlayer (235)    Back cover (240)