Organic Solar Cell (OPV) Materials

　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’.