A method for making an ultra-thin, flexible crystalline silicon solar cell from thick, inflexible cells. A thick, inflexible cell having a plurality of electrical contacts on the back side thereof is adhered to a mount by means of a temporary bonding adhesive tape and a thickness of the mounted stack. A thickness of the bonding tape and the back-side contacts is determined and compared to a desired thickness of the final cell. Excess material is ground from the front side of the stack to obtain a thinned stack having the desired thickness and the thinned stack is removed from the mount to produce an ultra-thin, flexible rear-contact Si solar cell having a total thickness of less than 80 μm and a bending radius of less than 20 mm. The front surface can be textured, with a passivation layer and/or a dielectric layer being deposited thereon.