Patent ID: 8575476

Claim:
A CIS solar cell, comprising: a substrate having an upper surface formed with unevenness; a CIS light absorbing layer adapted to absorb light; and an upper electrode disposed above the CIS light absorbing layer, wherein the CIS light absorbing layer is disposed on the substrate and in contact with the unevenness, so that the substrate serves as a lower electrode, wherein the substrate is comprised of an alloy of Ni and Mo or Co and Mo, wherein an alloy composition of an upper side of the substrate is different from an alloy composition of a lower side of the substrate, wherein the alloy composition of the substrate is configured so that the linear expansion coefficient of the alloy substrate as a whole is equal to the linear expansion coefficient of the CIS light absorbing layer, and wherein a lower surface side of the substrate comprises a Ni-rich or a Co-rich phase and the upper surface side of the substrate comprises a Mo-rich phase and a region of the substrate between the lower surface side and the upper surface side of the substrate comprises Mo diffused with Ni or Co wherein the Mo concentration becomes higher from the lower surface side of the substrate to the upper surface side of the substrate, the upper surface being in contact with the CIS light absorbing layer.