Abstract: A flexible substrate has heat resistance to endure the high temperature such as sintering of a photovoltaic conversion layer of a compound-type thin film solar cell, can prevent permeation and/or diffusion of metal into the photovoltaic conversion layer, and can be used for many applications. The polyimide layer-containing flexible substrate has a metal substrate of metal foil made of ordinary steel or stainless steel having a coefficient of thermal expansion in a plane direction of not more than 15 ppm/K, or a metal substrate of metal foil made of that ordinary steel or stainless steel on the surface of which a metal layer comprising one of copper, nickel, zinc, or aluminum or an alloy layer of the same is provided, over which a polyimide layer having a layer thickness of 1.5 to 100 ?m and a glass transition point temperature of 300 to 450° C. is formed.

Abstract: The present invention provides a laminate structure with little warping comprised of a stainless steel foil, a resin, and a metal foil, that is, a laminate structure comprised of a three-layer structure of a stainless steel foil, a resin, and a metal foil wherein the stainless steel foil is comprised of mixed phases of a ferromagnetic phase and a nonferromagnetic phase and the ratio of the ferromagnetic phase is 0.1 mass % to 4.0 mass %.