High efficient and stabilized photovoltaics via morphology manipulating in active layer by rod-coil block copolymers comprising different hydrophilic to hydrophobic dielectric blocks

Abstract

The poly(3-hexylthiophene) (P3HT)-based block copolymers were synthesized with hydrophilic and hydrophobic dielectric blocks including poly(ethylene glycol) (PEG), poly(methyl methacrylate) (PMMA), and poly(styrene) (PS), and employed as morphology modifiers (10–80wt%) in P3HT: phenyl-C71-butyric acid methyl ester (PC71BM) bulk heterojunction (BHJ) solar cells. The advantages and drawbacks of the coily blocks were also outlined from perspective of photovoltaic characteristics. A novel matrix-bridged disperses model was proposed to map out well-connected BHJ networks, which was consistent with the scattering data. Rod-coil block copolymers simultaneously controlled some main properties, i.e., crystallinity, d-spacing, domain sizes, and stability. Hydrophobic-based block copolymers (P3HT-b-PS and P3HT-b-PMMA) increased crystallinity, P3HT crystallite size, and PC71BM cluster size and decreased d-spacings. This reflected larger and denser P3HT crystallites and coarser and more packed PC71BM clusters. P3HT crystallites grew up to ∼60 and 30nm in (100) and (020) directions, respectively. In 30wt% of P3HT7150-b-PS, PC71BM clusters were also the largest (=38.87nm). A fully interdigitated hexyl chains (10.05Å) was acquired in 80wt% of P3HT7150-b-PS. Impressing trends of the P3HT-b-PMMA copolymers resembled that of P3HT-b-PS ones, but with a smoother slope. In contrast, hydrophilic-based block copolymers (P3HT-b-PEG and P3HT-b-PEG-b-P3HT) resulted in finer and looser P3HT crystallites and PC71BM clusters. The largest d-spacings in the directions of the hexyl side chains (=19.97Å) and π-π stacking (=4.95Å) were detected in 80wt% of P3HT7150-b-PEG750. The lowest (=3.51Å) and highest (=5.63Å) d-spacings for PC71BM clusters appeared in 80wt% of P3HT7150-b-PS and P3HT7150-b-PEG750, respectively. Unlike PEG-based block copolymers, in P3HT-b-PS and P3HT-b-PMMA ones, lower P3HT molecular weights conduced to higher power conversion efficiencies (PCE=4.43%). The short current density (Jsc=11.68mA/cm2), open circuit voltage (Voc=0.63V), and fill factor (FF=63%) were maximized in well-modified photovoltaic devices.