[en] A low-cost, environmentally benign method was used to prepare nanostructured thin films of Co₅(OH)₈(NO₃)₂.2H₂O, 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/Co₅(OH)₈(NO₃)₂.2H₂O/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 μA/cm², 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.