A New-Type Photovoltaic Cell Using Photochemical Reaction of Fullerene

Abstract

Fullerene, C60, is readily reduced to its anion radical, C60, in nitrobenzene (NB) containing tetraalkylammonium tetraphenylborate (TAATPB) under irradiation with visible light. Fullerene is excited from the singlet state to the triplet state by visible light and the excited C60 withdraws one electron from TPB to form C60, while TPB is decomposed to biphenyl and diphenyl boric acid through TPB. C60 can be kept at least for several days without any change in NB deaerated with argon gas. However, as soon as the NB solution containing C60 is bubbled with air, C60 is immediately oxidized to C60. Remarking this photochemical reaction of C60, we have developed a new-type photovoltaic cell, which has two functions of generation and storage of electricity. In this presentation, we show this photovoltaic cell developed in this work and discuss its performance for generation and storage of electricity. Figure 1 shows a schematic diagram of the photovoltaic cell. The anodic reaction is oxidation of C60 to C60, i. e., C60 → C60 + e. On the other hand, we chose a reduction reaction from permanganate ion to manganese ion in aqueous 1 M sulfuric acid as a cathodic reaction, i. e., MnO4 + 8H + 5e → Mn + 4H2O, though many reduction reactions were possible. Consequently, a total reaction of the photovoltaic cell is MnO4 + C60 + 8H → Mn + 5C60 + 4H2O. The photovoltaic cell is represented by Pt | 1 mM C60, 0.1 M TPATPB, 0.2 M TBAClO4 in NB || 10 mM MnO4 in aqueous 1 M sulphuric acid, 1 M perchlorate acid | Pt. Here, TBA indicates tetrabutylammonium ion. Perchlorate ion was added in both phases to increase the electric conductivity. When the photovoltaic cell was irradiated with visible light ranging from 400 to 700 nm (26 mWcm), the electromotive force was measured to be ca. 0.8 V and the electric current of ca. 3 mA was observed. Increasing the concentration of MnO4 in the aqueous phase and the electrode area of the anode, the electric current of ca. 10 mA was achieved continuously at least for an hour.