2,2′-Bis(1,3,4-thiadiazole)-Based π‑Conjugated Copolymers for Organic Photovoltaics with Exceeding 8% and Its Molecular Weight Dependence of Device Performance

A series of novel π-conjugated copolymers based on 2,2′-bis­(1,3,4-thiadiazole) (BTDz) have been developed. Among them, the BTDz-based donor–acceptor alternating copolymer with the (<i>E</i>)-1,2-di­(3-(2-ethyl­hexyl)­thiophene)­vinylene donor unit (PBTDzTV) exhibited a high solubility and high crystallinity. PBTDzTVs favorably self-assembled, forming face-on and edge-on multibilayer structures in thin nanoscale films. The relative volume fractions of these structures varied depending on the polymer’s molecular weight. The higher molecular weight polymer formed a higher volume fraction of the face-on structure; in particular, the polymer with a 26.6 kDa of number-average molecular weight made only the face-on structure. The device performance was improved as the polymer molecular weight and the volume fraction of the face-on structure increased. The bulk-heterojunction photovoltaic device based on PBTDzTV:PC₇₁BM demonstrated the high power conversion efficiency (PCE) of 8.04% when the device was fabricated with the highest molecular weight polymer having the face-on structure

Synthesis, Thermal Properties, and Morphologies of Amphiphilic Brush Block Copolymers with Tacticity-Controlled Polyether Main Chain

A series of brush block copolymers (BBCPs) consisting of poly­(decyl glycidyl ether) (PDGE) and poly­(10-hydroxyldecyl glycidyl ether) (PHDGE) blocks, having four different types of chain tacticities, i.e., [<i>at</i>-PDGE]-<i>b</i>-[<i>at</i>-PDEGE], [<i>at</i>-PDGE]-<i>b</i>-[<i>it</i>-PDEGE], [<i>it</i>-PDGE]-<i>b</i>-[<i>at</i>-PDEGE], and [<i>it</i>-PDGE]-<i>b</i>-[<i>it</i>-PDEGE], where the <i>it</i> and <i>at</i> represent the isotactic and atactic chains, respectively, were prepared by <i>t</i>-Bu-P₄-catalyzed sequential anionic ring-opening polymerization of glycidyl ethers followed by side-chain modification. The corresponding homopolymers, i.e., <i>at</i>-PDGE, <i>it</i>-PDGE, <i>at</i>-PHDGE, and <i>it</i>-PHDGE, were also prepared for comparison with the BBCPs. The PDGE homopolymers were significantly promoted in the phase transitions and morphological structure formation by the isotacticity formation. In particular, <i>it</i>-PDGE was found to form only a horizontal multibilayer structure with a monoclinic lattice in thin films, which was driven by the bristles’ self-assembling ability and enhanced by the isotacticity. However, the PHDGE homopolymers were found to reveal somewhat different behaviors in the phase transitions and morphological structure formation by the tacticity control due to the additional presence of a hydroxyl group in the bristle end as an H-bonding interaction site. The H-bonding interaction could be enhanced by the isotacticity formation. The <i>it</i>-PHDGE homopolymer formed only the horizontal multibilayer structure, which was different from the formation of a mixture of horizontal and tilted multibilayer structures in <i>at</i>-PHDGE. The structural characteristics were further significantly influenced by the diblock formation and the tacticity of the counterpart block. Because of the strong self-assembling characteristics of the individual block components, all the BBCPs formed separate crystals rather than cocrystals. The isotacticity always promoted the formation of better quality morphological structures in terms of their lateral ordering and orientation