NOVELTY - The thin film photovoltaic device comprises a transparent substrate (12) comprising a borosilicate glass that has a thickness of 0.5-2.5 mm, a thin film stack comprising a transparent conductive oxide layer, a photovoltaic heterojunction and back contact layer, and a composite encapsulation material (18) placed on the thin film stack. The encapsulation material defines rib elements (19), and is positioned such that the rib element extends away from the thin film stack. The rib elements entirely extend across a length of the encapsulation material in a rib direction.    USE - Used as thin film photovoltaic device such as a solar module.    ADVANTAGE - The thin film photovoltaic device can be economically manufactured with high reliability, strength and stiffness and without any bowing.    DETAILED DESCRIPTION - The thin film photovoltaic device comprises a transparent substrate (12) comprising a borosilicate glass that has a thickness of 0.5-2.5 mm, a thin film stack comprising a transparent conductive oxide layer, a photovoltaic heterojunction and back contact layer, and a composite encapsulation material (18) placed on the thin film stack. The encapsulation material defines rib elements (19), and is positioned such that the rib element extends away from the thin film stack. The rib elements entirely extend across a length of the encapsulation material in a rib direction, and have a peak-to-trough distance of 0.5-10 mm. The thin film stack is positioned between the borosilicate glass and the encapsulation material, and defines scribes oriented in a scribe direction and separating the thin film stack into photovoltaic cells. The rib direction that is parallel or perpendicular to the scribe direction. The thin film photovoltaic device further comprises a back substrate positioned between the encapsulation material and the thin film stack, and an adhesive layer (16) positioned between the thin film stack and the composite encapsulation material. The encapsulation material comprises a web of fibers. The rib elements: are defined by the encapsulation material; are parallel to each other; form a continuous wave extending across the encapsulation material; and are oriented to intersect each other. The transparent substrate has a first volumetric thermal expansion coefficient. The encapsulation material has a second volumetric thermal expansion coefficient that is present plus minus 40% of the first volumetric thermal expansion coefficient. The web comprises carbon fibers, fiberglass fibers and/or para-aramid synthetic fibers.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic cross-sectional view of a thin film photovoltaic device.    Transparent substrate (12)    Adhesive layer (16)    Encapsulation material (18)    Rib elements (19)    Valley. (21)