NOVELTY - The method for fabricating flexible thin film III-V compound solar cells (100), comprises receiving a substrate (400) previously used to form the III-V compound solar cell, forming a sacrificial layer (420) on the reused substrate, forming an active layer (110A) of a wafer-sized III-V compound solar cell on the sacrificial layer, forming a backing layer (120) on the solar cell, and removing the sacrificial layer from between the wafer-sized solar cell and the substrate to separate the wafer-sized thin film III-V compound solar cell from the substrate on a wafer sized scale.    USE - The method is useful for fabricating flexible thin film III-V compound solar cells.    ADVANTAGE - The method ensures effective fabrication of flexible thin film III-V compound solar cells with light weight and high thermal conductivity without decreasing the yield and increasing the risk of damaging the structure of the thin film II-V compound solar cell during handling, and increases the efficiency of the solar cell.    DETAILED DESCRIPTION - The method for fabricating flexible thin film III-V compound solar cells (100), comprises receiving a substrate (400) previously used to form the III-V compound solar cell, forming a sacrificial layer (420) on the reused substrate, forming an active layer (110A) of a wafer-sized III-V compound solar cell on the sacrificial layer, forming a backing layer (120) on the solar cell, removing the sacrificial layer from between the wafer-sized solar cell and the substrate to separate the wafer-sized thin film III-V compound solar cell from the substrate on a wafer sized scale, forming a (n)th active layer on the (n-1)st active layer where n is the total number of active layers and is an integer greater than one, applying surface metallization to the active layer, and applying an antireflection coating to the active layer. The substrate and the active layer are formed from III-V compound. The substrate is previously used in the fabrication of another thin film III-V compound solar cell. The backing layer is formed of a composite of metal and polymer. The removing step comprises immersing the substrate, sacrificial layer, active layer and backing layer in an acid etch solution to dissolve the sacrificial layer. The flexible III-V compound solar cell comprises a thin film multiple junction III-V compound solar cell having multiple junctions. An INDEPENDENT CLAIM is included for a method for forming a thin film multiple junction III-V compound solar cell.    DESCRIPTION OF DRAWING(S) - The diagram shows a thin film III-V solar cell.    Thin film III-V compound solar cell (100)    Active layer (110A)    Backing layer (120)    Substrate (400)    Sacrificial layer. (420)