A prototype of organic photovoltaics (OPV) was reported by Tang et al. in 1986.1) In order to fabricate an OPV device, we can use highly productive methods such as printing and roll-to-roll methods. The OPV device usually requires a bulk heterojunction (BHJ) which can be fabricated by mixing an electron-donor (p-type semiconductor) and electron-acceptor (n-type semiconductor).2) The former material involves a π-conjugated polymer and a small molecule semiconductor, and the latter material is normally a fullerene derivative. PCBM, that is a solubility-enhanced fullerene, efficiently provides a bulk heterojunction.3) ICBM gives a high open-circuit voltage because it has a higher energy LUMO than that of PCBM.4) A C70 derivative usually gives higher cell efficiency compared with that of the corresponding C60 one, because the C70 derivative absorbs light better than the C60.5) We can introduce an acceptor component into the structure of a p-type semiconducting polymer to form a donor-acceptor (DA-type) polymer, that shows light absorption in the long wavelength area based on a charge transfer.6) Raw materials for π-conjugated polymers are listed in the section of ‘Building Blocks for Semiconducting Polymer’.
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