NOVELTY - The solar cell stack fabrication method comprises forming a nanopatterned polymeric layer on a first surface of a silicon wafer, etching the first surface of the silicon wafer using a dry etching process and a wet etching process to transfer a pattern of the nanopatterned polymeric layer to the first surface of the silicon wafer for forming a nanopatterned first surface of the silicon wafer having recessions and protrusions, cleaning the nanopatterned first surface of the silicon wafer, and forming a reflective electrode material layer on a second surface of the silicon wafer.    USE - The method is useful for fabricating a solar cell stack.    ADVANTAGE - The method is capable of easily fabricating the solar cell stack with reduced size, increased production yield, improved power conversion efficiency, enhanced light absorption and output current characteristics and less number of processing steps.    DETAILED DESCRIPTION - The solar cell stack fabrication method comprises forming a nanopatterned polymeric layer on a first surface of a silicon wafer, etching the first surface of the silicon wafer using a dry etching process and a wet etching process to transfer a pattern of the nanopatterned polymeric layer to the first surface of the silicon wafer for forming a nanopatterned first surface of the silicon wafer having recessions and protrusions, cleaning the nanopatterned first surface of the silicon wafer, forming a reflective electrode material layer on a second surface of the silicon wafer that is opposite to the nanopatterned first surface of the silicon wafer, buffered oxide etching the nanopatterned first surface of the silicon wafer, treating the nanopatterned first surface of the silicon wafer to decrease a contact angle (40-50 degrees ) of water on the nanopatterned first surface of the silicon wafer, depositing electron donor material on the nanopatterned first surface of the silicon wafer to form an electron donor layer (178) on the nanopatterned first surface of the silicon wafer, and depositing a transparent electrode material on the electron donor layer to form a transparent electrode layer on the electron donor layer. The treatment of the nanopatterned first surface of the silicon wafer comprises UV ozone treatment of the silicon wafer. A resistivity of the silicon wafer following the UV ozone treatment is less than or equal to 120% of the resistivity of the silicon wafer before the UV ozone treatment. The deposition of the electron donor material comprises electrodepositing the electron donor material in recessions of the nanopatterned first surface of the silicon wafer. The method further comprises patterning a surface of a substrate (172) to form a nanopatterned surface, depositing a conformal layer of a reflective electrode material on the nanopatterned surface of the substrate, depositing a conformal layer of a first electrically conductive organic material on the reflective electrode material, depositing a layer of a second electrically conductive organic material on the first electrically conductive organic material, depositing a buffer material on the second electrically conductive organic material, and depositing a second buffer material between the reflective electrode material and the first electrically conductive organic material. The deposition of the layer of the second electrically conductive organic material comprises filling recesses and covering protrusions in the conformal layer of the first electrically conductive organic material with the second electrically conductive organic material. INDEPENDENT CLAIMS are included for:    (1) a solar cell stack; and    (2) a solar cell comprising a solar cell stack.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross section of an organic solar cell comprising a solar cell stack.    Organic solar cell (170)    Patterned substrate (172)    Reflective electrode (174)    Electron acceptor layer (176)    Electron donor layer (178)    Transparent electrode. (182)