Biselenophene Imide: Enabling Polymer Acceptor with High Electron Mobility for High-Performance All-Polymer Solar Cells.

The shortage of narrow band gap polymer acceptors with high electron mobility is the major bottleneck for developing efficient all-polymer solar cells (all-PSCs). Herein, we synthesize a distannylated electron-deficient biselenophene imide monomer (BSeI-Tin) with high purity/reactivity, affording an excellent chance to access acceptor-acceptor (A-A) type polymer acceptors. Copolymerizing BSeI-Tin with dibrominated monomer Y5-Br, the resulting A-A polymer PY5-BSeI shows a higher molecular weight, narrower band gap, deeper-lying frontier molecular orbital levels and larger electron mobility than the donor-acceptor type counterpart PY5-BSe. Consequently, the PY5-BSeI-based all-PSCs deliver a remarkable efficiency of 17.77 % with a high short-circuit current of 24.93 mA cm-2 and fill factor of 75.83 %. This efficiency is much higher than that (10.70 %) of the PY5-BSe-based devices. Our study demonstrates that BSeI is a promising building block for constructing high-performance polymer acceptors and stannylation of electron-deficient building blocks offers an excellent approach to developing A-A type polymers for all-PSCs and even beyond.

Semiconducting Polymers Based on Simple Electron-Deficient Cyanated trans-1,3-Butadienes for Organic Field-Effect Transistors.

Developing high-performance but low-cost n-type polymers remains a significant challenge in the commercialization of organic field-effect transistors (OFETs). To achieve this objective, it is essential to design the key electron-deficient units with simple structures and facile preparation processes, which can facilitate the production of low-cost n-type polymers. Herein, by sequentially introducing fluorine and cyano functionalities onto trans-1,3-butadiene, we developed a series of structurally simple but highly electron-deficient building blocks, namely 1,4-dicyano-butadiene (CNDE), 3-fluoro-1,4-dicyano-butadiene (CNFDE), and 2,3-difluoro-1,4-dicyano-butadiene (CNDFDE), featuring a highly coplanar backbone and deep-positioned lowest unoccupied molecular orbital (LUMO) energy levels (-3.03-4.33 eV), which render them highly attractive for developing n-type semiconducting polymers. Notably, all these electron-deficient units can be easily accessed by a two-step high-yield synthetic procedure from low-cost raw materials, thus rendering them highly promising candidates for commercial applications. Upon polymerization with diketopyrrolopyrrole (DPP), three copolymers were developed that demonstrated unipolar n-type transport characteristics in OFETs with the highest electron mobility of >1 cm2  V-1 s-1 . Hence, CNDE, CNFDE, and CNDFDE represent a class of novel, simple, and efficient electron-deficient units for constructing low-cost n-type polymers, thereby providing valuable insight for OFET applications.

Over 18.2% efficiency of layer-by-layer all-polymer solar cells enabled by homoleptic iridium(III) carbene complex as solid additive.

The vertical phase distribution of active layers plays a vital role in balancing exciton dissociation and charge transport for achieving efficient polymer solar cells (PSCs). The layer-by-layer (LbL) PSCs are commonly prepared by using sequential spin-coating method from donor and acceptor solutions with distinct solvents and solvent additives. The enhanced exciton dissociation is expected in the LbL PSCs with efficient charge transport in the relatively neat donor or acceptor layers. In this work, a series of LbL all-polymer solar cells (APSCs) were fabricated with PM6 as donor and PY-DT as acceptor, and triplet material m-Ir(CPmPB)3 is deliberately incorporated into PY-DT layer to prolong exciton lifetimes of active layers. The power conversion efficiency (PCE) of LbL APSCs is improved to 18.24% from 17.32% by incorporating 0.3 wt% m-Ir(CPmPB)3 in PY-DT layer, benefiting from the simultaneously enhanced short-circuit current density (JSC) of 25.17 mA cm-2 and fill factor (FF) of 74.70%. The enhancement of PCE is attributed to the efficient energy transfer of m-Ir(CPmPB)3 to PM6 and PY-DT, resulting in the prolonged exciton lifetime in the active layer and the increased exciton diffusion distance. The efficient energy transfer from m-Ir(CPmPB)3 to PM6 and PY-DT layer can be confirmed by the increased photoluminescence (PL) intensity and the prolonged PL lifetime of PM6 and PY-DT in PM6 + m-Ir(CPmPB)3 and PY-DT + m-Ir(CPmPB)3 films. This study indicates that the triplet material as solid additive has great potential in fabricating efficient LbL APSCs by prolonging exciton lifetimes in active layers.