Advanced Poly(ethylene glycol)/polythiophene globular nanostructures in P3HT:PCBM photovoltaics

Abstract

Abstract Semiglobular and globular nanostructures were designed by conducting the isothermal crystallization on dilute solutions of Y-type poly(ethylene glycol) (PEG)-b-polythiophene (PTh)2 and PEG-b-poly(3-dodecyl thiophene) (PDDTh)2 copolymers. The semiglob(PEG-star-PTh) (6–25 nm) and glob(PEG-star-PDDTh) (5–16 nm) nanostructures were then employed as the morphology compatibilizers in active layers of poly(3-hexylthiophene) (P3HT):phenyl-C71-butyric acid methyl ester (PC71BM) solar cells. The incorporation of pre-designed glob(PEG-star-PDDTh) (11.25 mA/cm2, 55%, 0.66 V, 8.7 × 10−5 cm2/V.s and 7.9 × 10−4 cm2/V.s) and semiglob(PEG-star-PTh) (13.03 mA/cm2, 60%, 0.69 V, 2.1 × 10−3 cm2/V.s and 1.5 × 10−2 cm2/V.s) nanostructures significantly improved the morphological and photovoltaic characteristics, leading to the efficacies of 4.08 and 5.39%, respectively. The ordered assemblies of polythiophenes, in particular the PTh backbones without any side chains, were capable of controlling the morphology in a better manner compared with the individual polymer chains. Although the PEG-b-(PDDTh)2 (8.7 ns) and PEG-b-(PTh)2 (9.8 ns) block copolymers increased the life time, the pre-designed glob(PEG-star-PDDTh) (14.5 ns) and semiglob(PEG-star-PTh) (19.1 ns) scrolled nanostructures further affected the reduction of charge trap states. The P3HT:PC71BM:semiglob(PEG-star-PTh) systems also demonstrated the lower charge transfer resistance (Rtr = 158 Ω cm2) with respect to the glob(PEG-star-PDDTh) based devices (309 Ω cm2).