Photoaction, temperature and O₂ depletion effects in fullerene photoelectrochemical solar cells

It is demonstrated that higher temperature and C₆₀ oxygen depletion increase the photocurrent of fullerene photoelectrochemical solar cells (PEC). Fullerene/iodide electrolyte PEC consisting of intrinsic single crystal C₆₀ in either aqueous 3 M KI, 0.01 M I₂, or 0.1 M tetrabutyl ammonium iodide, 0.3 M LiClO₄ in acetonitrile solution, drive regenerative photoinduced iodide oxidation. The photocurrent is increased by an order of magnitude (to 6.4 μA/cm² under 100 mW/cm² illumination) by an increase of the aqueous cell temperature from 24°C to 82°C. A similar order of magnitude increase in photocurrent is accomplished by O₂ depletion pretreatment (24 h at 400°C in Ar) of the C₆₀ to improve conductivity. However, this latter treatment also irreversibly increases the cell dark current. The spectral action of single crystal C₆₀ is also probed, through the generated photoelectrochemical current in iodide, ferricyanide and sulfuric electrolytes as a function of wavelength. Band edges are observed at 720 nm (1.7 eV) and 560 nm (2.2 eV), and a substantial peak photocurrent response occurs at 395 nm (3.1 eV) and decreases at shorter wavelengths.