Over the past three decades, significant research efforts have focused on improving the charge carrier mobility of organic thin-film transistors (OTFTs). In recent years, a commonly observed nonlinearity in OTFT current-voltage characteristics, known as the "kink" or "double slope," has led to widespread mobility overestimations, contaminating the relevant literature. Here, published data from the past 30 years is reviewed to uncover the extent of the field-effect mobility hype and identify the progress that has actually been achieved in the field of OTFTs. Present carrier-mobility-related challenges are identified, finding that reliable hole and electron mobility values of 20 and 10 cm V s , respectively, have yet to be achieved. Based on the analysis, the literature is then reviewed to summarize the concepts behind the success of high-performance p-type polymers, along with the latest understanding of the design criteria that will enable further mobility enhancement in n-type polymers and small molecules, and the reasons why high carrier mobility values have been consistently produced from small molecule/polymer blend semiconductors. Overall, this review brings together important information that aids reliable OTFT data analysis, while providing guidelines for the development of next-generation organic semiconductors.

The development of nonfullerene acceptors (NFAs), which are used to replace fullerene derivatives in organic solar cells (OSCs) due to their extended light absorption and tunable energy levels, has seen impressive progress in the past few years. [1][2][3][4] A range of new NFAs with different building blocks and geometrical dimensions has been designed to boost the power conversion efficiency (PCE) of OSCs. Among the highest performing NFAs, linear rod-like acceptor-donor-acceptor (A-D-A) structures incorporating fused ladder-type aromatics have attracted much interest. Common donor units include 4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene (IDT) [5][6][7][8][9] and 6,12-dihydro-dithienoindeno [10][11][12][13][14][15][16][17][18] In both cases, the fused core facilitates π-electron delocalization and improves the π-π stacking between molecules, hence enhancing the intrinsic charge carrier mobility.In 2015, Zhan and coworkers reported a new NFA, 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11--b′]dithiophene (ITIC) (Scheme 1), which is comprised an electron-donating IDTT-based core flanked by two electron-withdrawing units of 1,1-dicyanomethylene-3-indanone (IC), that exhibited a promising PCE of 6.8% at that time. [10] Since then, many strategies have been applied to modify the structure of ITIC in order to adjust the absorption spectra and energy levels to further improve the PCE, for example, by changing the side chains, [17,18] extending the conjugation length, [19][20][21][22] and substituting the end acceptor groups. [13][14][15][16] To date, a few systems based on these NFAs have achieved a PCE of over 10%. [5,[13][14][15]18,20,22] However, it is noticeable that in all cases these NFAs incorporate phenylalkyl or thienylalkyl side chains as the solubilizing groups on the fused core. These aryl-based side chains facilitate the synthesis of the IDTT core under Friedel-Crafts conditions via the formation of stable triaryl cations. However, since the nature of the side chains has a

Improving the charge carrier mobility of solution‐processable organic semiconductors is critical for the development of advanced organic thin‐film transistors and their application in the emerging sector of printed electronics. Here, a simple method is reported for enhancing the hole mobility in a wide range of organic semiconductors, including small‐molecules, polymers, and small‐molecule:polymer blends, with the latter systems exhibiting the highest mobility. The method is simple and relies on admixing of the molecular Lewis acid B(C6F5)3 in the semiconductor formulation prior to solution deposition. Two prototypical semiconductors where B(C6F5)3 is shown to have a remarkable impact are the blends of 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene:poly(triarylamine) (diF‐TESADT:PTAA) and 2,7‐dioctyl[1]‐benzothieno[3,2‐b][1]benzothiophene:poly(indacenodithiophene‐co‐benzothiadiazole) (C8‐BTBT:C16‐IDTBT), for which hole mobilities of 8 and 11 cm2 V−1 s−1, respectively, are obtained. Doping of the 6,13‐bis(triisopropylsilylethynyl)pentacene:PTAA blend with B(C6F5)3 is also shown to increase the maximum hole mobility to 3.7 cm2 V−1 s−1. Analysis of the single and multicomponent materials reveals that B(C6F5)3 plays a dual role, first acting as an efficient p‐dopant, and secondly as a microstructure modifier. Semiconductors that undergo simultaneous p‐doping and dopant‐induced long‐range crystallization are found to consistently outperform transistors based on the pristine materials. Our work underscores Lewis acid doping as a generic strategy towards high performance printed organic microelectronics.

A novel rigid donor monomer, indacenodithieno[3,2‐b]thiophene (IDTT), containing linear alkyl chains, is reported. Its copolymer with benzothiadiazole is an excellent p‐type semiconductor, affording a mobility of 6.6 cm2 V−1 s−1 in top‐gated field‐effect transistors with pentafluorobenzenethiol‐modified Au electrodes. Electrode treatment with solution‐deposited copper(I) thiocyanate (CuSCN) has a beneficial hole‐injection/electron‐blocking effect, further enhancing the mobility to 8.7 cm2 V−1 s−1.

Understanding the key factors influencing the mechanical and electrical properties of semiconducting polymers is crucial to the development of stretchable electronics. In this work, a high-mobility diketopyrrolopyrrole-based conjugated polymer with varied number-average molecular weights (M n ) was used as the model system to explore the impact of molecular weight on the electrical and mechanical properties. Higher-M n films are more ductile and stretchable. Both hole mobilities of thin-film transistors and elastic modulus become maximum at a moderate M n of 88 kg/mol. It was found that film continuity, entanglements, and relative degree of crystallinity are critical factors for approaching the best device performance and highest elastic modulus. The transition molecular weight of a given polymer semiconductor is the key to achieving stretchable high-mobility transistors that are practically useful. This work would help to offer guidance to manipulate the mechanical and electrical properties for other polymer semiconductors.

High-performance unipolar n-type conjugated polymers (CPs) are critical for the development of organic electronics. In the current paper, four "weak donor-strong acceptor" n-type CPs based on pyridine flanked diketopyrrolopyrrole (PyDPP), namely PPyDPP1-4FBT, PPyDPP2-4FBT, PPyDPP1-4FTVT, and PPyDPP2-4FTVT, are synthesized via direct arylation polycondensation by using 3,3′,4,4′-tetrafluoro-2,2′-bithiophene (4FBT) or (E)-1,2-bis(3,4difluorothien-2-yl)ethene (4FTVT) as weak donor unit. All four polymers exhibit low-lying highest occupied molecular orbital (≈ −5.90 eV) and lowest unoccupied molecular orbital energy levels (≈ −3.70 eV). Top-gate/ bottom-contact organic field-effect transistors based on all four polymers display unipolar n-channel characteristics with electron mobility (µ e ) above 1 cm 2 V −1 s −1 in air, and presented linear |I SD | 1/2 −V GS plots and weak dependence of the extracted moblity on gate voltage (V GS ), indicative of the reliability of the extracted mobility values. Importantly, the devices based on PPyDPP1-4FBT and PPyDPP2-4FBT show a pure unipolar n-channel transistor behavior as revealed by the typical unipolar n-channel output characteristics and clear off-regimes in transfer characteristics. Attributed to its high crystallinity and favorable thin film morphology, PPyDPP2-4FBT shows the highest µ e of 2.45 cm 2 V −1 s −1 , which is among the highest for unipolar n-type CPs reported to date. This is also the first report for DPP based pure n-type CPs with µ e greater than 1 cm 2 V −1 s −1 .

The displacement of fluoride by cyanide offers a simple route to strongly electron accepting cyano substituted benzothiadiazole monomers. Copolymerisation with electron rich donors leads to low band gap polymers which exhibit electron transporting behaviour.

We report the synthesis of two new selenophene-containing ladder-type monomers, cyclopentadiselenophene (CPDS) and indacenodiselenophene (IDSe), via a 2-fold and 4-fold Pd-catalyzed coupling with a 1,1-diborylmethane derivative. Copolymers with benzothiadiazole were prepared in high yield by Suzuki polymerization to afford materials which exhibited excellent solubility in a range of nonchlorinated solvents. The CPDS copolymer exhibited a band gap of just 1.18 eV, which is among the lowest reported for donor-acceptor polymers. Thin-film transistors were fabricated using environmentally benign, nonchlorinated solvents, with the CPDS and IDSe copolymers exhibiting hole mobility up to 0.15 and 6.4 cm V s, respectively. This high performance was achieved without the undesirable peak in mobility often observed at low gate voltages due to parasitic contact resistance.