By considering the qualitative benefits associated with solution rheology and mechanical properties of polymer semiconductors, it is expected that polymer-based electronic devices will soon enter our daily lives as indispensable elements in a myriad of flexible and ultra low-cost flat panel displays. Despite more than a decade of research focused on designing and synthesizing state-of-the-art polymer semiconductors for improving charge transport characteristics, the current mobility values are still not sufficient for many practical applications. The confident mobility in excess of ∼10 cm(2)/V·s is the most important requirement for enabling the realization of the aforementioned near-future products. We report on an easily attainable donor-acceptor (D-A) polymer semiconductor: poly(thienoisoindigo-alt-naphthalene) (PTIIG-Np). An unprecedented mobility of 14.4 cm(2)/V·s, by using PTIIG-Np with a high-k gate dielectric poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)), is achieved from a simple coating processing, which is of a magnitude that is very difficult to obtain with conventional TFTs by means of molecular engineering. This work, therefore, represents a major step toward truly viable plastic electronics.

1wileyonlinelibrary.com more than 1 cm 2 V −1 s −1 . [ 1,2 ] Furthermore, several recent papers have reported that mobility values surpassing 3 cm 2 V −1 s −1 can be obtained in state-of-the-art donoracceptor (D-A) polymers based on diketopyrrolopyrrole (DPP). The DPP motif not only contributes to tight π−π spacing but also enhances the charge delocalization through its high level of co-planarity and quinoidal structure, being highly benefi cial to charge-carrier transport through intermolecular hopping. [ 2a , 3 ] Even though their stability in ambient electrochemical oxidative processes is necessary for the broadbased, high-value applications mentioned above, solution-processable polymeric semiconductors performing beyond the current levels-reliably exceeding 10 cm 2 V −1 swith an on/off ratio ( I on / I off ) of at least 10 6 -are the most compelling requirement for the progress of organic electronics.Recently, we and other groups suggested the effectiveness of controlling the branching point of the side chain from the polymer backbone for tuning intermolecular self-assembly and charge-carrier mobility. [ 3a-c,4 ] Therefore, side-chain engineering can be as important as manipulating the conjugated building blocks in the backbones when designing high-performance conjugated polymers. [ 5 ] In this work, we report the substantially enhanced charge-transport characteristics of a series of DPP-based polymers showing vastly superior FET performance (hole mobilities ( µ h ) of 12.25 cm 2 V −1 s −1 and I on / I off ≥ 10 6 together with electron mobilities ( µ e ) larger than 2 cm 2 V −1 s −1 ). These have been achieved by simply modulating the side-chain branching position (i.e., replacing the commonly used 2-octyldodecyl solubilizing group as the β -branched chain of the DPPbased polymers with the 5-octylpentadecyl chain ( ε -branched chain)). We also demonstrate the structure−property relationships regarding the interplay of the molecular packing and macroscopic charge-transport effi cacy. Results and Discussion Synthesis and CharacterizationBriefl y, 5-octyl-1-pentadecyliodide as the key ε -branched side chain ( ε -C 8 C 15 ) was obtained from commercially available ) with an on/off ratio ( I on / I off ) of at least 10 6 are achieved in the FETs fabricated using the polymers. The developed polymers exhibit extraordinarily high electrical performance with both hole and electron mobilities superior to that of unipolar amorphous silicon.

A synergetic effect of molecular weight (Mn) and fluorine (F) on the performance of all‐polymer solar cells (all‐PSCs) is comprehensively investigated by tuning the Mn of the acceptor polymer poly((N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl)‐alt‐5,5′‐(2,2′‐bithiophene)) (P(NDI2OD‐T2)) and the F content of donor polymer poly(2,3‐bis‐(3‐octyloxyphenyl)quinoxaline‐5,8‐dyl‐alt‐thiophene‐2,5‐diyl). Both Mn and F variations strongly influence the charge transport properties and morphology of the blend films, which have a significant impact on the photovoltaic performance of all‐PSCs. In particular, the effectiveness of high Mn in increasing power conversion efficiency (PCE) can be greatly improved by the devices based on optimum F content, reaching a PCE of 7.31% from the best all‐PSC combination. These findings enable us to further understand the working principles of all‐PSCs with a view on achieving even higher power conversion efficiency in the future.

Systematic creation of polymeric semiconductors from novel building blocks is critical for improving charge transport properties in organic fi eld-effect transistors (OFETs). A series of ultralow-bandgap polymers containing thienoisoindigo (TIIG) as a thiophene analogue of isoindigo (IIG) is synthesized. The UV-Vis absorptions of the TIIG-based polymers ( PTIIG-T , PTIIG-Se , and PTIIG-DT ) exhibit broad bands covering the visible to near-infrared range ofup to 1600 nm. All the polymers exhibit unipolar p-channel operations with regard to gold contacts. PTIIG-DT with centrosymmetric donor exhibits a maximum mobility of 0.20 cm 2 V − 1 s − 1 under gold contacts, which is higher than those of the other polymers containing axisymmetric donors. Intriguingly, OFETs fabricated with aluminum electrodes show ambipolar charge transport with hole and electron mobilities of up to 0.28 ( PTIIG-DT ) and 0.03 ( PTIIG-T ) cm 2 V − 1 s − 1 , respectively. This is a record value for the hitherto reported TIIG-based OFETs. The fi nding demonstrates that TIIG-based polymers can potentially function as either unipolar or ambipolar semiconductors without reliance on the degree of electron affi nity of the co-monomers.

The introduction of fluorine (F) atoms onto conjugated polymer backbone has verified to be an effective way to enhance the overall performance of polymer-based bulk-heterojunction (BHJ) solar cells, but the underlying working principles are not yet fully uncovered. As our attempt to further understand the impact of F, herein we have reported two novel fluorinated analogues of PCDTBT, namely, PCDTFBT (1F) and PCDT2FBT (2F), through inclusion of either one or two F atoms into the benzothiadiazole (BT) unit of the polymer backbone and the characterization of their physical properties, especially their performance in solar cells. Together with a profound effect of fluorination on the optical property, nature of charge transport, and molecular organization, F atoms are effective in lowering both the HOMO and LUMO levels of the polymers without a large change in the energy bandgaps. PCDTFBT-based BHJ solar cell shows a power conversion efficiency (PCE) of 3.96 % with high open-circuit voltage (VOC) of 0.95 V, mainly due to the deep HOMO level (-5.54 eV). To the best of our knowledge, the resulting VOC is comparable to the record VOC values in single junction devices. Furthermore, to our delight, the best PCDTFBT-based device, prepared using 2 % v/v diphenyl ether (DPE) additive, reaches the PCE of 4.29 %. On the other hand, doubly-fluorinated polymer PCDT2FBT shows the only moderate PCE of 2.07 % with a decrease in VOC (0.88 V), in spite of the further lowering of the HOMO level (-5.67 eV) with raising the number of F atoms. Thus, our results highlight that an improvement in efficiency by tuning the energy levels of the polymers by means of molecular design can be expected only if their truly optimized morphologies with fullerene in BHJ systems are materialized.

The π-extended (E)-2-(2-(thiophen-2-yl)-vinyl)­thiophene (TVT)-based polymers are an interesting class of semiconducting polymers because of their excellent mobilities and unique film microstructures. Despite these properties, the effect of the side-chain regiochemistry of TVT skeletons on the intrinsic properties of these polymers remains unclear. To investigate this, in this study, hexyl-substituted TVT subunits with a “tail in (TI)” or “tail out (TO)” regiosymmetrical arrangement were first introduced into diketo­pyrrolopyrrole (DPP)-based copolymer main chains to afford “isomeric” polymers PI and PO, respectively. By combining optical spectroscopy, atomic force microscopy (AFM), and grazing incidence X-ray diffraction (GIXD) data, we quantitatively characterized the aggregation, crystallization, and backbone orientation of both polymer films, which were then correlated to the charge-carrier mobilities. The PI film exhibited a bimodal packing motif comprising a mixture of edge-on and face-on orientations, which was beneficial for three-dimensional (3D) charge transport and resulted in a hole mobility 2-fold larger than that in the PO film (μh = 1.69 cm2 V–1 s–1). This comparative study substantiates the important role of the regiochemistry of TVT in developing high-performance semiconducting polymers.

Diketopyrrolopyrrole derivatives containing phenyl and thiophene units adorned with alkoxynaphthalene (Naph-PDPP and Naph-TDPP) were synthesized by a Suzuki cross-coupling reaction. SKP measurements were carried out upon exposure to different VOCs.

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