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Addition reaction between C60 and ethylenediamine occurred at room temperature in an ambient condition. C60-ethylenediamine adduct particles were prepared by mixing toluene solutions of C60 and ethyelenediamine. Average diameter of the C60-ethylenediamine adduct particles was changed non-linearly according to the reaction time, which were observed using transmission electron microscopy. Early stage of the reaction, the diameter of the adduct particles was changed from about 250 to about 430 nm. Then, the size of the adduct particles was converged to about 300 nm. During this addition reaction, the crystalline sizes of adduct particles were constant about 2–3 nm, regardless of the sizes of the adduct particles, which were determined by X-ray diffraction measurement.

Organic-inorganic hybrid heterojunction solar cells containing perovskite CH3NH3PbI3 using Nb, Ta, or V-doped TiO2 as electron-transporting layers were fabricated and characterized. By Nb doping, the conductivity and carrier density of the TiO2 increased, and its flat-band potential showed a positive shift. The short-circuit current density and power conversion efficiency of perovskite solar cells were improved by using Ti0.95Nb0.05O2 compared to undoped TiO2.

Insoluble fullerene-diamine adduct thin-films consisting of C60 and 1,2-diaminoethane were easily fabricated on an electrode by an alternate immersion process. Formation of the C60-diamine adduct films were confirmed using transmission absorption spectroscopy and atomic force microscopy. An inverted-type organic solar cells were fabricated by using the C60-diamine adduct film as the electron transport layer. The resultant photoelectric conversation performance of the solar cells suggested that photocurrent is generated via the photoexcitation of polythiophene. The result suggests that the present insoluble fullerene-diamine adduct films worked as buffer layer for organic thin-film solar cells.

Organic-inorganic hybrid heterojunction solar cells containing perovskite CH3NH3PbI3 using Nb-doped TiO2 as an electron-transporting layer were fabricated and characterized. Nb-doped TiO2 layer showed an improvement of the short-circuit current density and power conversion efficiency using Ti0.95Nb0.05O2.

Thin films of a C60–ethylenediamine (EDA) adduct were prepared from an EDA solution of the adduct particles. An inverted-type organic thin-film solar cell using the thin film of the C60–EDA adduct as a buffer layer was fabricated. The solar cell performance suggested that the C60–EDA adduct thin film functioned as an electron-transporting layer, similarly to the titanium oxides in typical inverted-type organic thin-film solar cells.