While the regioregularity (RR) of conjugated polymers is known to have a strong influence on their inherent properties, systematic study of the RR effect has been limited due to the lack of a synthetic methodology. Herein, we successfully produced a series of poly(3-hexylthiophene)s (P3HTs) having a wide range of RR from 64 to 98%. Incorporation of controlled amounts of head-to-head (H−H) coupled dimer in modified Grignard metathesis polymerization allows a facile tuning of the RR of the P3HTs with comparable molecular weight and low polydispersity. Then, we investigated the effect of RR on structural, electrical, and mechanical properties of P3HTs in which a higher content of H−H regio-defects, namely lower RR, systematically lowered the degree of crystallinity. Although high RR P3HT (98%) had higher charge carrier mobility (1.81 × 10 −1 cm 2 V −1 s −1 ), its strong crystallinity induced high brittleness and stiffness, resulting in device failure under a very small strain, as shown in tensile and bending tests. The tensile modulus was reduced significantly from 287 MPa (RR 98%) to 13 MPa (RR 64%), and also the RR 64% P3HT film had much better mechanical resilience with an order of magnitude higher elongation at break than that of the RR 98% polymer. Our findings suggest that the mechanical and electrical properties of conjugated polymers can be systematically tuned by controlling the RR to meet the purposes of various organic electronic applications, i.e., flexible portable devices vs high-performance panels.

We examined the packing structure of polystyrene-coated gold nanoparticles (Au@PS) as a function of grafting density. A series of Au@PS nanoparticles with grafting densities in the range of 0.51−1.94 chains nm −2 were prepared by a ligand exchange process using thiol-terminated PS and then selfassembled at a liquid−air interface. We observed a transition from disordered to bodycentered cubic (bcc) to face-centered cubic (fcc) arrangements with increasing grafting density, even though the ligand length-to-core radius ratio (λ) was as high as 3.0, a condition that typically favors nonclose-packed bcc symmetry in the self-assembly of hard nanoparticles. To explain this phenomenon, we define λ eff to include the concentrated polymer brush regime as part of the "hard core", which predicts that the softness of Au@PS nanoparticles is reduced from 1.53 to 0.14 in a theta solvent as the grafting density increases from 0.51 to 1.94 chains nm −2 . This new definition of λ can also predict the effective radii of nanoparticles using the established optimal packing model. The experimental findings are supported by a combination of coarse-grained molecular dynamics simulation and adaptive common neighbor analysis, which show that changes in grafting density can drive the observed transitions in nanoparticle packing. These studies provide new insights for controlling the selfassembled symmetries of polymer-coated nanocrystals using a simple ligand exchange process to tune particle softness.

In this work, we develop mechanically robust and high-performance organic thin-film transistors (OTFTs) based on poly­(3-hexylthiophene) (P3HT) regioblock copolymers (block-P3HTs). These block-P3HTs consist of regioregular (rre) and regiorandom (rra) P3HTs, where the highly crystalline rre block allows efficient charge transport while the amorphous rra block provides mechanical robustness and interdomain connection. To examine the effects of the molecular architecture on the OTFT performance and stretchability, we prepare a series of block-P3HTs having different number-average molecular weight (M n) values of rra blocks (from 0 to 32 kg mol–1) and a fixed M n of rre blocks (11 kg mol–1). Thin films of all of the block-P3HTs exhibit a high charge-carrier mobility due to the formation of well-developed edge-on crystallites from the rre blocks confined within the rra domains, leading to a hole mobility of 1.5 × 10–1 cm2 V–1 s–1, which is superior to that of the rre P3HT homopolymer. In addition, the mechanical toughness of block-P3HT thin films is remarkably enhanced by the rra block. While the rre P3HT homopolymer thin film shows a brittle behavior with an elongation at break of only 0.3%, the elongation at break of the block-P3HT thin films increases by a factor of 100, yielding 30.2% with increasing M n of the rra block, without sacrificing the electrical properties. In particular, a noticeable enhancement of both elongation at break and toughness is observed between M n values of the rra block of 8 and 20 kg mol–1, indicating that the critical molecular weight of rra P3HT plays an important role in determining the mechanical response of the block-P3HT thin films. This study provides guidelines and strategies to improve the mechanical properties of organic electroactive materials without the disruption of optoelectrical properties, which is critical to fabricate high-performance soft electronics.

In this work, we present a facile strategy that combines the merits of both fullerene-PSCs and all-PSCs to significantly increase the PCE of the all-PSCs without compromising mechanical performance.