Photovoltaic cells based on ternary P3HT:PCBM: Ruthenium(II) complex bearing 8-(diphenylphosphino)quinoline active layer

Optical, morphological and photovoltaic properties are investigated for ternary solar cells containing a traditional poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C₆₁-butyric-acid-methyl ester (P3HT:PCBM) bulkheterojunction (BHJ) active layer modified with different concentrations of a novel ruthenium complex [Ru(N-P)₂(O-O)], where N-P abbreviates 8-(diphenylphosphino)quinolone and O-O = oxalate dianion. At a low concentration of the Ru-complex (2.5 wt%) the device efficiency is improved by 50% compared with the reference binary devices at ambient conditions. This substantial efficiency enhancement is attributed to the role of the Ru-complex in improving light absorption over a wavelength range of (295–800 nm) in combination with a better matching of the energy levels of the ternary blend system. Moreover, at low concentration, the Ru-complex has a positive impact on the morphology of the active layer in the device. The inclusion of Ru-complex increases the P3HT crystallinity substantially with virtually no effect on the size and orientation of the crystalline lamellae. The enhancement in device efficiency becomes less pronounced with increasing the concentration of the Ru-complex due to the formation of several micron-size domains of [Ru(N-P)₂(O-O)] in the ternary active layers. These large domains negatively affect the optical properties and morphology, thus inhibiting efficient charge generation and transport in the corresponding solar cells.