Highly efficient, lightweight, and flexible III-V compound multi-junction solar cells play an important role in the wearable electronic field. GaInP/GaAs/InGaAs inverted metamorphic (IMM) solar cells directly grown on an N-doped GaAs substrate by a GaInP etch stop layer were fabricated. The AlGaInAs graded buffer layer is grown to relax the strain of InGaAs with GaAs. Most misfit dislocations are localized at the internal interfaces of the graded buffer and do not appear to propagate. Then, the solar cells are fabricated by the copper-plated process, and Cu thin films serve as not only the flexible support but also the P-type electrode. The device had a total thickness of less than 35 mu m, a mass density of less than 0.03 g/cm(2), and can exhibit excellent bendability. Under the AM1.5G solar illumination, the thin film solar cell has the best photovoltaic conversion efficiency of 33.13% with the Voc of 2.86 V, a Jsc value of 13.55 mA/cm(2), and a FF of 85.49%. This method can be used to prepare flexible thin film solar cells simply and efficiently.