NOVELTY - A polymeric solar cell comprises: (a) a first electrode comprising an electrically conductive polymer composite, e.g. cellulose or a cellulose derivative; (b) a second electrode comprising a composite polymer semiconductor, e.g. polyphenylacetylene or a derivative, or polystyrene or a derivative, or a metal polystyrene nanoparticle.    USE - A polymeric solar cell (claimed).    ADVANTAGE - The cellulose-polymer composite solar cell is biodegradable and fabricated using environmentally friendly materials and methods.    DETAILED DESCRIPTION - A polymeric solar cell comprises: (a) a first electrode comprising an electrically conductive polymer composite, where the electrically conductive polymer composite comprises: (a.i) cellulose or a cellulose derivative; (a.ii) a conductive polymer or conductive polymer composite; and (a.iii) optionally, a first electrically conductive dopant; (b) a second electrode comprising a composite polymer semiconductor, where the composite polymer semiconductor comprises: (b.i) cellulose or a cellulose derivative; (b.ii) polyphenylacetylene or a derivative, or polystyrene or a derivative, or a metal polystyrene nanoparticle; and (b.iii) optionally, a second electrically conductive dopant. INDEPENDENT CLAIMS are included for:    (1) dissolving cellulose or a cellulose derivative in a phosphonium ionic liquid which involves: (i) mixing the cellulose or cellulose derivative with the ionic liquid under conditions for the dissolution of the cellulose or cellulose derivative in the ionic liquid; and (ii) obtaining a cellulose composite comprising the cellulose or cellulose derivative incorporated with the ionic liquid;    (2) a composite polymer semiconductor, comprising: (a) cellulose or a cellulose derivative; (b) polyphenylacetylene or a polyphenylacetylene derivative; and (c) optionally, an electrically conductive dopant; and    (3) solvent-free preparation of polyphenylacetylene polymer or a derivative which involves polymerizing phenylacetylene or a phenylacetylene derivative in the presence of a free radical initiator, under conditions for the solvent-free polymerization of the phenylacetylene or phenylacetylene derivative, where the polyphenylacetylene or derivative is prepared in greater than 70% yield, where the polymerization occurs in 4 hours or less.