High‐Performance n‐Channel Organic Transistors Using High‐Molecular‐Weight Electron‐Deficient Copolymers and Amine‐Tailed Self‐Assembled Monolayers

While high‐performance p‐type semiconducting polymers are widely reported, their n‐type counterparts are still rare in terms of quantity and quality. Here, an improved Stille polymerization protocol using chlorobenzene as the solvent and palladium(0)/copper(I) as the catalyst is developed to synthesize high‐quality n‐type polymers with number‐average molecular weight up to 10⁵ g mol^?1. Furthermore, by sp²‐nitrogen atoms (sp²‐N) substitution, three new n‐type polymers, namely, pBTTz, pPPT, and pSNT, are synthesized, and the effect of different sp²‐N substitution positions on the device performances is studied for the first time. It is found that the incorporation of sp²‐N into the acceptor units rather than the donor units results in superior crystalline microstructures and higher electron mobilities. Furthermore, an amine‐tailed self‐assembled monolayer (SAM) is smoothly formed on a Si/SiO₂ substrate by a simple spin‐coating technique, which can facilitate the accumulation of electrons and lead to more perfect unipolar n‐type transistor performances. Therefore, a remarkably high unipolar electron mobility up to 5.35 cm² V^?1 s^?1 with a low threshold voltage (≈1 V) and high on/off current ratio of ≈10⁷ is demonstrated for the pSNT‐based devices, which are among the highest values for unipolar n‐type semiconducting polymers.     

Self‐Assembled Monolayer Transistors

Self‐assembled monolayers of organic, conjugated molecules can be used as active components of field‐effect transistors. The length of the molecule can define critical device dimensions with high precision on the nanometer scale. Transistor effects on the molecular‐scale as well as in devices consisting of single active molecules have been demonstrated. The observed device performance indicates that such transistors might be useful for switching and amplifying electrical signals in logic circuits. Moreover, functionalizing the organic molecules reveals that different parts of the molecule can act as gate insulator or the active component of transistors. Such research might pave the way to molecular electronic applications.     

Complementary Logic Circuits Based on High‐Performance n‐Type Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) have been the subject of intense research in recent years. To date, however, most of the reported OECTs rely entirely on p‐type (hole transport) operation, while electron transporting (n‐type) OECTs are rare. The combination of efficient and stable p‐type and n‐type OECTs would allow for the development of complementary circuits, dramatically advancing the sophistication of OECT‐based technologies. Poor stability in air and aqueous electrolyte media, low electron mobility, and/or a lack of electrochemical reversibility, of available high‐electron affinity conjugated polymers, has made the development of n‐type OECTs troublesome. Here, it is shown that ladder‐type polymers such as poly(benzimidazobenzophenanthroline) (BBL) can successfully work as stable and efficient n‐channel material for OECTs. These devices can be easily fabricated by means of facile spray‐coating techniques. BBL‐based OECTs show high transconductance (up to 9.7 mS) and excellent stability in ambient and aqueous media. It is demonstrated that BBL‐based n‐type OECTs can be successfully integrated with p‐type OECTs to form electrochemical complementary inverters. The latter show high gains and large worst‐case noise margin at a supply voltage below 0.6 V.     

High‐Performance All‐Polymer Solar Cells Enabled by an n‐Type Polymer Based on a Fluorinated Imide‐Functionalized Arene

A novel imide‐functionalized arene, di(fluorothienyl)thienothiophene diimide (f‐FBTI2), featuring a fused backbone functionalized with electron‐withdrawing F atoms, is designed, and the synthetic challenges associated with highly electron‐deficient fluorinated imide are overcome. The incorporation of f‐FBTI2 into polymer affords a high‐performance n‐type semiconductor f‐FBTI2‐T, which shows a reduced bandgap and lower‐lying lowest unoccupied molecular orbital (LUMO) energy level than the polymer analog without F or with F‐functionalization on the donor moiety. These optoelectronic properties reflect the distinctive advantages of fluorination of electron‐deficient acceptors, yielding “stronger acceptors,” which are desirable for n‐type polymers. When used as a polymer acceptor in all‐polymer solar cells, an excellent power conversion efficiency of 8.1% is achieved without any solvent additive or thermal treatment, which is the highest value reported for all‐polymer solar cells except well‐studied naphthalene diimide and perylene diimide‐based n‐type polymers. In addition, the solar cells show an energy loss of 0.53 eV, the smallest value reported to date for all‐polymer solar cells with efficiency > 8%. These results demonstrate that fluorination of imide‐functionalized arenes offers an effective approach for developing new electron‐deficient building blocks with improved optoelectronic properties, and the emergence of f‐FBTI2 will change the scenario in terms of developing n‐type polymers for high‐performance all‐polymer solar cells.