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Developing low‐cost and high‐performance n‐type polymer semiconductors is essential to accelerate the application of organic thermoelectrics (OTEs). To achieve this objective, it is critical to design strong electron‐deficient building blocks with simple structure and easy synthesis, which are essential for the development of n‐type polymer semiconductors. Herein, we synthesized two cyano‐functionalized highly electron‐deficient building blocks, namely 3,6‐dibromopyrazine‐2‐carbonitrile (CNPz) and 3,6‐Dibromopyrazine‐2,5‐dicarbonitrile (DCNPz), which feature simple structures and facile synthesis. CNPz and DCNPz can be obtained via only one‐step reaction and three‐step reactions from cheap raw materials, respectively. Based on CNPz and DCNPz, two acceptor–acceptor (A–A) polymers, P(DPP‐CNPz) and P(DPP‐DCNPz) are successfully developed, featuring deep‐positioned lowest unoccupied molecular orbital (LUMO) energy levels, which are beneficial to n‐type organic thin‐film transistors (OTFTs) and OTEs performance. An optimal unipolar electron mobility of 0.85 and 1.85 cm2 V−1 s−1 is obtained for P(DPP‐CNPz) and P(DPP‐DCNPz), respectively. When doped with N‐DMBI, P(DPP‐CNPz) and P(DPP‐DCNPz) show high n‐type electrical conductivities/power factors of 25.3 S cm−1/41.4 μW m−1 K−2, and 33.9 S cm−1/30.4 μW m−1 K−2, respectively. Hence, the cyano‐functionalized pyrazine CNPz and DCNPz represent a new class of structurally simple, low‐cost and readily accessible electron‐deficient building block for constructing n‐type polymer semiconductors. [ABSTRACT FROM AUTHOR]

Polythiophenes, built on head‐to‐head (HH) linked 3,3′‐oligomer ethylene glycol‐2,2′‐bithiophene (gT2), have simple chemical structure, good backbone planarity, and relatively high‐lying the lowest unoccupied molecular orbital (LUMO) energy levels, hence showing excellent p‐type performance in organic electrochemical transistors (OECTs) with µC* of several hundred F cm−1 V−1 s−1. In this study, sequential cyano substitution is utilized to enable transformation of charge carrier polarity from p‐type to n‐type in OECTs, based on the parent polythiophene g4T2‐T2. With the increase of cyano group number, the polythiophenes exhibit gradually lowered LUMO levels from −2.55 to −3.90 eV. As a result, from g4T2‐T2 to CNg4T2‐CNT2, the p‐type performance dramatically diminishes accomplished by the enhancement of n‐type one when applied in OECTs. To the authors' delight, polymer CNg4T2‐CNT2 with the highest content of cyano groups exhibits a remarkable n‐type µC* of 27.01 F cm−1 V−1 s−1 and high gm,norm of 6.75 S cm−1 with negligible p‐type character. This study demonstrates that sequential cyano substitution provides a powerful approach for developing high‐performance n‐type polymers for OECT applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The development of high‐performance n‐type polymer semiconductors is powered by the design and synthesis of electron‐deficient building blocks with optimized physicochemical properties. By meticulously installing an imide group onto fluorene and its cyanated derivative, we report here two very electron‐deficient building blocks, imide‐functionalized fluorenone (FOI) and its cyanated derivative (FCNI), both featuring a deep‐lying lowest unoccupied molecular orbital energy level down to −4.05 eV and highly coplanar framework, endowing them ideal units for constructing n‐type polymers. Thus, a series of polymers are built from them, exhibiting unipolar n‐type transport character with a highest electron mobility of 0.11 cm2 V−1 s−1. Hence, FOI and FCNI offer a remarkable platform for accessing high‐performance n‐type polymers and the imide functionalization of appropriate (hetero)arenes is a powerful strategy for developing polymers with deep‐lying LUMOs for n‐type organic electronics. [ABSTRACT FROM AUTHOR]

High‐performance nonfullerene ternary organic solar cells (OSCs) with two polymer donors are less frequently reported because of the limited numbers of efficient polymer donors with good compatibility. Herein, a wide‐bandgap polymer P1 with a deep‐lying highest occupied molecular orbital (HOMO) level is incorporated as the third component into the benchmark PM6:Y6 binary system to fabricate ternary OSCs. The introduction of P1 not only leads to extended absorption coverage and forms a cascade‐like energy level alignment but also shows excellent compatibility with PM6, resulting in a favorable morphology in the ternary blend. More importantly, P1 possesses a deeper HOMO level (−5.6 eV) than most well‐known donor polymers, which enables resulting ternary OSCs with an improved open‐circuit voltage. As a result, the optimized ternary OSCs with 40 wt% P1 in donors achieve a power conversion efficiency (PCE) of 16.2% with a small nonradiative recombination loss of 0.23 eV, which is among the highest values of ternary OSCs based on two polymer donors. In addition, the ternary OSCs show a broad composition tolerance with a high PCE of over 14% throughout the whole blend ratios. These results provide an effective approach to fabricate efficient ternary OSCs by synergizing two wide‐bandgap polymer donors. [ABSTRACT FROM AUTHOR]

n-Type polymer semiconductors are essential for enabling high-performance organic electronic devices; however, their development still remains a challenge. Herein, we reported a new electron-deficient building block, i.e. bithiophene imide (BTI)-bridged isoindigo (IID), BTIID, through a Knoevenagel condensation reaction between the bisaldehyde BTI and the alkylated indolinones. Three donor-acceptor (D-A) copolymers were then successfully synthesized via standard Stille coupling reaction based on this novel building block, which exhibit highly planar backbones and low-lying lowest unoccupied molecular orbitals (LUMO) energy levels. When integrated into organic field-effect transistors (OFETs), these polymers demonstrated unipolar n-type transport characteristics with a highest electron mobility of 5.79 × 10−4 cm2 V−1 s−1. Our research results indicate that the design of strong electron-withdrawing units via integrating two different electron-acceptor units into one single structure represents a promising strategy for developing n-type polymer semiconductors with low-lying LUMO energy levels. • Two polymers based on NDP-AB as electron deficient units were synthesized and characterized for the first time. • With low LUMO energy of -4.24 eV, endowing the semiconductor layer with the ability to form Ohmic contacts with electrodes. • NDP-AB-based polymers exhibit n-type behavior with electron transport mobility up to 0.89 cm2 V−1 s−1. [ABSTRACT FROM AUTHOR]