NOVELTY - The assembly comprises a polyimide film (12) having a thickness of 5-150 microns, an electrode (16) supported by the polyimide film, a copper indium gallium diselenide (CIGS)/copper indium sulfide (CIS) light absorber layer (14), and monolithically integrated CIGS/CIS photovoltaic cells. The polyimide film comprises a block copolymer polyimide derived from: 75 mol.% an aromatic dianhydride component consisting of rigid rod dianhydride and/or non-rigid rod dianhydride; and 70 mol.% an aromatic diamine component consisting of rigid rod diamine and/or non-rigid rod diamine.    USE - The assembly is useful in thin film photovoltaic solar cells.    ADVANTAGE - The assembly is lightweight, reduces the cost of the manufacture of the solar cell, increases the conversion efficiency, ruggedness, reliability and performance of the cell, eliminates or avoids the occurrence of defects such as electrical shorts to the solar cell.    DETAILED DESCRIPTION - The assembly comprises a polyimide film (12) having a thickness of 5-150 microns, an electrode (16) supported by the polyimide film, a copper indium gallium diselenide (CIGS)/copper indium sulfide (CIS) light absorber layer (14), and monolithically integrated CIGS/CIS photovoltaic cells. The polyimide film comprises a block copolymer polyimide derived from: 75 mol.% an aromatic dianhydride component consisting of rigid rod dianhydride and/or non-rigid rod dianhydride; and 70 mol.% an aromatic diamine component consisting of rigid rod diamine and/or non-rigid rod diamine, and a sub-micron filler that has a dimension of less than 400 nm and an aspect ratio of greater than 3:1, is less than the polyimide film thickness in all dimensions and is present in an amount of 10-45 vol.% of the polyimide film. The mole ratio of dianhydride to diamine is 48-52:52-48 and the ratio of X:Y is 20-80:80-20, where X is the mole percent of rigid rod dianhydride and rigid rod diamine, and Y is the mole percent of non-rigid rod dianhydride and non-rigid rod diamine based upon the total dianhydride component and total diamine component of the polyimide. The electrode is located between the light absorber layer and the polyimide film, and is present in electrical communication with the light absorber layer. The sub-micron filler is coated with a coupling agent and/or a dispersant.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of a thin-film solar cell fabricated on a polyimide film.    Polyimide film (12)    Light absorber layer (14)    Electrode (16)    Transparent conducting oxide layer (23)    Grid contact. (24)