A low-cost, environmentally benign method was used to prepare nanostructured thin films of Co(5)(OH)(8) (NO(3))(2)center dot 2H(2)O, a layered double hydroxide p-type semiconductor. When infilled with poly(3-butylthiophene) (P3BT), an n-type semiconducting polymer, the resulting hybrid bulk heterojunction yields a photovoltaic device. The indium-doped tin oxide/Co(5)(OH)(8)(NO(3))(2)center dot 2H(2)O/P3BT/Al cell described here is an unprecedented example of an optoelectronic device fabricated by a low-cost biologically inspired pathway independent of organic structure-directing agents. Under illumination, this proof-of-principle device yields an open circuit voltage of 1.38 V, a short circuit current of 9 mu A/cm(2), a fill factor of 26% and a power efficiency of 3.2.10(-3)%. While the open circuit voltage of this prototype cell is close to its theoretical maximum, potential sources of the observed low efficiency are identified, and a suggested path for improvement is discussed. (C) 2009 Elsevier B.V. All rights reserved.