Bulk heterojunction solar cells with internal quantum efficiency approaching 100%

Abstract

We report the fabrication and measurement of solar cells with 6% power conversion efficiency using the alternating co-polymer, poly[N-9 ''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole) (PCDTBT) in bulk heterojunction composites with the fullerene derivative [6,6]-phenyl C(70)-butyric acid methyl ester (PC(70)BM). The PCDTBT/PC(70)BM solar cells exhibit the best performance of any bulk heterojunction system studied to date, with J(SC) = 10.6 mA cm(-2), V(OC) = 0.88 V, FF = 0.66 and eta(e) = 6.1% under air mass 1.5 global (AM 1.5 G) irradiation of 100 mW cm(-2). The internal quantum efficiency is close to 100%, implying that essentially every absorbed photon results in a separated pair of charge carriers and that all photogenerated carriers are collected at the electrodes.