NOVELTY - A solar cell comprises a substrate (100) including p-n junction formed in it; a buffer layer (103) formed on backside of substrate, where a groove (104) is formed in buffer layer; and a metal layer attached on buffer layer and filled into the groove. The substrate includes silicon wafer. The materials of buffer layer includes silicon dioxide, silicon nitride and/or silicon oxynitride. The metal layer is made by aluminum metal or aluminum alloy. The metal layer comprises first metal layer and second metal layer. The solar cell further comprises an anti-reflection layer.    USE - As solar cell (claimed) used as optoelectronic semiconductor device for transforming light into electricity; and in space industry.    ADVANTAGE - The buffer layer formed on the backside of the substrate reduces the stress of the structure stemming from thinner structure of the solar cell thereby eliminating the bending effect caused by the stress. The solar cell with thin structure has high transform efficiency. The buffer layer formed on backside of the substrate, changes the stress of the structure, strengthens the structure of the solar cell, and ameliorates the capability of releasing the stress or strain. The solar cell exhibits high surface area.    DETAILED DESCRIPTION - A solar cell comprises a substrate (100) including p-n junction formed in it; a buffer layer (103) formed on the backside of the substrate, where a groove (104) is formed in the buffer layer; and a metal layer attached on the buffer layer and filled into the groove. The substrate includes a silicon wafer. The materials of the buffer layer includes silicon dioxide, silicon nitride and/or silicon oxynitride. The thickness of the buffer layer is 50-100 nm. The laser include Ar laser, Q-switched ruby laser, Q-switched Alexandrite laser, Q-switched Nd:YAG laser or Frequency-doubled Q-switched Nd/YAG laser. The metal layer is made by aluminum metal or aluminum alloy. The metal layer comprises first metal layer and second metal layer. The solar cell further comprises an anti-reflection layer formed under the n-doped area. The materials of the anti-reflection layer includes cerium oxide, aluminum oxide, silicon nitride or silicon nitride-titanium dioxide.    DESCRIPTION OF DRAWING(S) - The figure shows cross-sectional view of several grooves in the buffer layer.    Substrate (e.g. silicon wafer) (100)    n-Junction (101)    p-Junction (102)    Buffer layer (103)    Groove (104)