No abstract

A record high OFET hole mobility, as high as 23.7 cm(2) /Vs, is achieved in macroscopic aligned semiconducting polymers. The high mobility is insensitive to the polymer molecular weight. Polymer chains are aligned along the fiber to facilitate intrachain charge transport.

Solution processable semiconducting polymers with excellent film forming capacity and mechanical flexibility are considered among the most progressive alternatives to conventional inorganic semiconductors. However, the random packing of polymer chains and the disorder of the polymer matrix typically result in low charge transport mobilities (10(-5)-10(-2) cm(2) V(-1) s(-1)). These low mobilities compromise their performance and development. Here, we present a strategy, by utilizing capillary action, to mediate polymer chain self-assembly and unidirectional alignment on nanogrooved substrates. We designed a sandwich tunnel system separated by functionalized glass spacers to induce capillary action for controlling the polymer nanostructure, crystallinity, and charge transport. Using capillary action, we demonstrate saturation mobilities with average values of 21.3 and 18.5 cm(2) V(-1 )s(-1) on two different semiconducting polymers at a transistor channel length of 80 μm. These values are limited by the source-drain contact resistance, Rc. Using a longer channel length of 140 μm where the contact resistance is less important, we measured μh = 36.3 cm(2) v(-1) s(-1). Extrapolating to infinite channel length where Rc is unimportant, the intrinsic mobility for poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5]thiadiazolo[3,4-c]pyridine] (Mn = 140 kDa) at this degree of chain alignment and structural order is μh ≈ 47 cm(2 )v(-1) s(-1). Our results create a promising pathway toward high performance, solution processable, and low-cost organic electronics.

Donor-acceptor conjugated polymers PBDT-DTBT and PBDT-DTNT, based on 2,1,3-benzothiadiazole (BT) and naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole (NT), have been designed and synthesized for polymer solar cells. NT contains two fused 1,2,5-thiadiazole rings that lower the band gap, enhance the interchain packing, and improve the charge mobility of the resulting polymer. Consequently, the NT-based polymer PBDT-DTNT exhibited considerably better photovoltaic performance with a power conversion efficiency (PCE) of 6.00% when compared with the BT-based polymer PBDT-DTBT, which gave a PCE of 2.11% under identical device configurations.

Domain purity and interface structure are known to be critical for fullerene‐based bulk heterojunction (BHJ) solar cells, yet have been very difficult to study. Using novel soft X‐ray tools, we delineate the importance of these parameters by comparing high performance cells based on a novel naphtha[1,2‐c:5,6‐c]bis[1,2,5]thiadiazole (NT) material to cells based on a 2,1,3‐benzothiadiazole (BT) analogue. BT‐based devices exhibit ∼15 nm, mixed domains that differ in composition by at most 22%, causing substantial bimolecular recombination. In contrast, NT‐based devices have more pure domains that are >80 nm in size, yet the polymer‐rich phase still contains at least 22% fullerene. Power conversion efficiency >6% is achieved for NT devices despite a domain size much larger than the nominal exciton diffusion length due to a favourable trade‐off in the mixed domain between exciton harvesting, charge transport, and bimolecular recombination. The miscibility of the fullerene with the NT and BT polymer is measured and correlated to the purity in devices. Importantly, polarized x‐ray scattering reveals preferential face‐on orientation of the NT polymer relative to the PCBM‐rich domains. Such ordering has previously not been observed in fullerene‐based solar cells and is shown here to be possibly a controlling or contributing factor to high performance.