The dependence of the cathode architecture on the photoactive layer morphology in bulk-heterojunction polymeric solar cells

Abstract

Poly (3-hexylthiophene) (P3HT), [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and polymethylmethacrylate (PMMA) have been chosen to prepare binary and ternary blend thin films. In the case of the binary blend thin films of P3HT:PCBM used as the photoactive layers, the LiF/Al cathode offered nearly the same power conversion efficiency (PCE) as bathocuproine (BCP) 2 nm Al−1 and BCP 10 nm Al−1 cathodes. While ternary blend thin films of P3HT:PCBM:PMMA were applied as the photoactive layers, the BCP 2 nm Al−1 cathode showed an increase of roughly 42% in the PCE relative to ternary blend thin film with LiF/Al and BCP 10 nm Al−1 cathodes. The vertical phase separation of P3HT and PCBM was found to be more suppressed in the ternary blend films than in the binary ones, due to the confinement of PMMA. The P3HT:PCBM:PMMA with the BCP 2 nm Al−1 cathode showed an increase of 20% in the PCE as compared to the binary thin film of P3HT:PCBM with the LiF/Al cathode. We provide some insights into the correlation between the morphology control of active layer and cathode structure, useful for the development of polymeric solar cells towards the commercialization.