Organic p-i-n solar cells having near infrared (NIR) sensitivity to 1050 nm were fabricated using a codeposited i-interlayer consisting of lead phthalocyanine (PbPc) and fullerene (C60). The external quantum efficiency and conversion efficiency for NIR light reached 43% (860 nm) and 2.3%, respectively. The codeposited i-interlayer was shown to have three separate nanostructural components each making a contribution to the operation of the cell. These were electron transport through amorphous C60, hole transport through the H-aggregates of PbPc, and carrier generation by NIR light at the J-aggregate sites of PbPc.

Conduction-type control of fullerene (C60) films from n- to p-type by doping with molybdenum oxide (MoO3) was demonstrated. The energetic value of the Fermi level, 4.60 eV, for nondoped C60 films measured by the Kelvin vibrating capacitor method was positively shifted to 5.88 eV, and approached the valence band by the coevaporated doping of MoO3 at a concentration of 3300 ppm. The existence of upward band bending of the Schottky junction formed at the interface between a metal and a p-type C60 film formed by MoO3 doping was confirmed based on its photovoltaic properties.

A novel method for crystallizing donor:acceptor blend films of small molecules in organic solar cells is developed. This method utilizes a liquid as a non‐sticking co‐evaporant during vacuum deposition. Striking enhancement in photocurrent generation is achieved in organic solar cells without exception, based on a variety of blend films produced by this method.

The film structure and electronic structure of a biradical hydrocarbon, diphenyl derivative of s-indacenodiphenalene (Ph(2)-IDPL) solid film has been investigated. A small energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) compared with that of typical π-conjugated small molecules was observed even for the amorphous film of Ph(2)-IDPL. This result indicates that the small HOMO-LUMO gap is an important characteristic of the singlet biradical electronic structure and well explains the previously reported ambipolar field effects of amorphous Ph(2)-IDPL film by Chikamatsu et al., Appl. Phys. Lett. 2007, 91, 043506. It was found that the gas-deposition method substantially improved the crystallinity of the film where Ph(2)-IDPL molecules form quasi one-dimensional (1D) molecular chains normal to the substrate surface. An extremely small HOMO-LUMO gap was observed in the polycrystalline Ph(2)-IDPL film, which is possibly caused by strong intermolecular coupling. The photon energy dependence of ultraviolet photoemission spectra shows that the stacked Ph(2)-IDPL molecular chain in the polycrystalline film develops an energy band structure in the direction of the surface normal of the film. The intermolecular covalency therefore evolves into the quasi 1D energy band along the molecular stacking direction.

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