n-Type Organic and Polymeric Semiconductors Based on Bithiophene Imide Derivatives

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: In the last three decades, p-type (hole-transporting) organic and polymeric semiconductors have achieved great success in terms of materials diversity and device performance, while the development of n-type (electron-transporting) analogues greatly lags behind, which is limited by the scarcity of highly electron-deficient building blocks with compact geometry and good solubility. However, such n-type semiconductors are essential due to the existence of the p−n junction and a complementary metal oxide semiconductor (CMOS)-like circuit in organic electronic devices. Among various electron-deficient building blocks, imide-functionalized arenes, such as naphthalene diimide (NDI) and perylene diimide (PDI), have been proven to be the most promising ones for developing n-type organic and polymeric semiconductors. Nevertheless, phenyl-based NDI and PDI lead to sizable steric hindrance with neighboring (hetero)arenes and a high degree of backbone distortion in the resultant semiconductors, which greatly limits their microstructural ordering and charge transport. To attenuate the steric hindrance associated with NDI and PDI, a novel imidefunctionalized heteroarene, bithiophene imide (BTI), was designed; however, the BTI-based semiconductors suffer from high-lying frontier molecular orbital (FMO) energy levels as a result of their electron-rich thiophene framework and monoimide group, which is detrimental to n-type performance.In this Account, we review a series of BTI derivatives developed via various strategies, including ring fusion, thiazole substitution, fluorination, cyanation, and chalcogen substitution, and elaborate the synthesis routes designed to overcome the synthesis challenges due to their high electron deficiency. After structural optimization, these BTI derivatives can not only retain the advantages of good solubility, a planar backbone, and small steric hindrance inherited from BTI but also have greatly suppressed FMO levels. These novel building blocks enable the construction of a great number of n-type organic and polymeric semiconductors, particularly acceptor−acceptor (or all-acceptor)-type polymers, with remarkable performance in various devices, including electron mobility (μ e ) of 3.71 cm 2 V −1 s −1 in organic thin-film transistors (OTFTs), a power conversion efficiency (PCE) of 15.2% in all-polymer solar cells (all-PSCs), a PCE of 20.8% in inverted perovskite solar cells (PVSCs), electrical conductivity (σ) of 0.34 S cm −1 and a power factor (PF) of 1.52 μW m −1 K −2 in self-doped diradicals, and σ of 23.3 S cm −1 and a PF of ∼10 μW m −1 K −2 in molecularly n-doped polymers, all of which are among the best values in each type of device. The structure−property−device performance correlations of these n-type semiconductors are elucidated. The design strategy and synthesis of these novel BTI derivatives provide important information for developing highly electron-deficient building blocks with optimized physicochemical properties. Finally, we offer o...

Cyano‐Functionalized n‐Type Polymer with High Electron Mobility for High‐Performance Organic Electrochemical Transistors

“…f‐BTI2g‐TVTCN exhibited a remarkable μ e,OTFT of 0.013 cm 2 V −1 s −1 which is the highest for n‐type polymers with OEG‐type side chains reported to date, but still much lower than the typical μ e,OTFT >1 cm 2 V −1 s −1 for BTI‐based polymers with alkyl side chains. [ 63 ] Introducing OEG‐type side chain is known to negatively affect μ e,OTFT , as well demonstrated by the systematic study of side chain effect in the NDI‐based P0−P100 polymer series. [ 39 ] This phenomenon is likely related to OEG‐type side chain introduced electron traps due to its hydrophilicity and interfacial charge‐transport density‐of‐states (DOS) broadening due to its high polarity.…”

“…Bithiophene imide (BTI) and its derivatives have been successful in developing high-performance n-type polymers with a highest OTFT electron mobility (μ e,OTFT ) > 3 cm 2 V −1 s −1 achieved, [63,64] and fused bithiophene imide dimer (f-BTI2) acceptor unit with branched oligo(ethylene glycol) (OEG)-type side chain was used in polymer f-BTI2TEG-FT to afford a high μ e,OECT of 0.034 cm 2 V −1 s −1 owing to its high degree of backbone planarity, favorable polymer chain orientation, and substantial electrochemical doping efficiency. [44] Recently, cyano functionalization has been used as a powerful method to build novel n-type polymers with low-lying lowest unoccupied molecular orbital (LUMO) energy levels and improved charge-transport capability, which has led to the successful development of excellent n-type polymers for high-performance OTFTs, organic thermoelectrics (OTEs), and all-polymer solar cells (all-PSCs).…”

Polymer Acceptors for High‐Performance All‐Polymer Solar Cells

“…Single‐crystal of the BTI model compound exhibited a highly planar backbone conformation with a short π‐π distance of 3.43 Å. Benefiting from such structural features and the strong electron‐withdrawing capacity of imide group, BTI unit was excellent acceptor building block for constructing a series of high‐performance polymer semiconductors, however these polymers mainly functioned as p‐type semiconductors since the LUMO is not sufficient low‐lying [26] . The open α and β positions of thiophenes in BTI offer a vast space for structure optimizations to lower the LUMO levels, which has substantially enriched the electron‐deficient building block library with good solubility and n‐type polymers built from them [27]…”

“…Benefiting from such structural features and the strong electron-withdrawing capacity of imide group, BTI unit was excellent acceptor building block for constructing a series of highperformance polymer semiconductors, however these polymers mainly functioned as p-type semiconductors since the LUMO is not sufficient low-lying. [26] The open α and β positions of thiophenes in BTI offer a vast space for structure optimizations to lower the LUMO levels, which has substantially enriched the electron-deficient building block library with good solubility and n-type polymers built from them. [27] A series of ladder-type BTI oligomers (BTIn, n = 2-5) with up to 15 rings and 5 imide groups were first successfully synthesized, which showed widely tunable FMO energy levels and aggregation properties.…”

A Vinylene‐Linker‐Based Polymer Acceptor Featuring a Coplanar and Rigid Molecular Conformation Enables High‐Performance All‐Polymer Solar Cells with Over 17% Efficiency

“…generations of all-PSCs typically employ polymer acceptors based on naphthalene diimide, perylene diimide, bithiophene imide or B←N bridge bipyridine moieties (Figure S1a, Supporting Information). [26][27][28][29] However, these groups of polymer acceptors usually suffer from some intrinsic flaws, including narrow absorption range, low extinction coefficient, relatively deep energy levels and unfavorable phase segregation, which limit the performance of corresponding all-PSCs. [30] To address these issues, a new type of polymer acceptor was first reported by Li et al who polymerized the prevailing indacenodithiophene-SMAs with aromatic linker units.…”