Photovoltaic properties of benzimidazole-derived perylene imides as an n-type material

Perylene imide derivatives were considered as an n-type material for a bulk-heterojunction solar cell. A perylene was modified to imide-imidazole derivatives comprised of a benzimidazole moiety with several polar substituents and a long alkyl chain for favorable electronic energy levels and solubility. The electron mobility of methoxy-derived imide-imidazole was measured to be 4.0 × 10− 3 cm/V s under an electric field of 320 V/cm, being nearly comparable to the hole mobility of poly(3-hexylthiophene) (P3HT). The hole and electron mobilities of a blend film made of P3HT and the methoxy derivative were closely balanced at ca. 3 × 10− 4 cm/V s. The power conversion efficiency of a photovoltaic cell using the blend film was improved with the increase in perylene content and reached 0.20%. The methoxy substitution at the imid-imidazole resulted in better power conversion efficiency than unsubstitution. On the contrary, an alkyl ester substitution provided a low conversion efficiency of less than 0.01% due to a small current from severe crystallization in a polymer blend film.