Charge carrier mobility is still the most challenging issue that should be overcome to realize everyday organic electronics in the near future. In this Communication, we show that introducing smart side-chain engineering to polymer semiconductors can facilitate intermolecular electronic communication. Two new polymers, P-29-DPPDBTE and P-29-DPPDTSE, which consist of a highly conductive diketopyrrolopyrrole backbone and an extended branching-position-adjusted side chain, showed unprecedented record high hole mobility of 12 cm(2)/(V·s). From photophysical and structural studies, we found that moving the branching position of the side chain away from the backbone of these polymers resulted in increased intermolecular interactions with extremely short π-π stacking distances, without compromising solubility of the polymers. As a result, high hole mobility could be achieved even in devices fabricated using the polymers at room temperature.

Systematic side-chain engineering has been performed for diketopyrrolopyrrole-selenophene vinylene selenophene (DPP-SVS) polymers to determine the optimal side-chain geometries for the most efficient charge transport, and the structure-property relationship has been thoroughly investigated using a range of analyses. A series of DPP-SVS polymers, ranging from 25-DPP-SVS to 32-DPP-SVS, with branched alkyl groups containing linear spacer groups from C2 to C9 has been synthesized, and the electrical performance of these polymers is significantly dependent on both the length of the spacer group and its odd-even characteristics. Spacer groups with even numbers of carbon atoms exhibit chargecarrier mobilities that are one order of magnitude higher than those with odd numbers of carbon atoms. The optimized charge transport has been obtained from 29-DPP-SVS with C6 spacer, showing the maximum mobility of 13.9 cm 2 V −1 s −1 (V GS , V DS = −100 V) and 17.8 cm 2 V −1 s −1 (V GS , V DS = −150 V). Longer spacer groups deviate from the odd-even trend. In addition to the exceptionally high charge-carrier mobilities of the DPP-SVS polymers, the results obtained herein provide new insight into the molecular design of high-performance polymer semiconductors.

A high-performance naphthalene diimide (NDI)-based conjugated polymer for use as the active layer of n-channel organic fi eld-effect transistors (OFETs) is reported. The solution-processable n-channel polymer is systematically designed and synthesized with an alternating structure of long alkyl substituted-NDI and thienylene-vinylene-thienylene units (PNDI-TVT). The material has a well-controlled molecular structure with an extended π -conjugated backbone, with no increase in the LUMO level, achieving a high mobility and highly ambient stable n-type OFET. The top-gate, bottomcontact device shows remarkably high electron charge-carrier mobility of up to 1.8 cm 2 V − 1 s − 1 ( I on / I off = 10 6 ) with the commonly used polymer dielectric, poly(methyl methacrylate) (PMMA). Moreover, PNDI-TVT OFETs exhibit excellent air and operation stability. Such high device performance is attributed to improved ππ intermolecular interactions owing to the extended π -conjugation, apart from the improved crystallinity and highly interdigitated lamellar structure caused by the extended ππ backbone and long alkyl groups.the morphology of the polymer fi lm, with its mixture of edge-on and face-on orientation, auto-encapsulation effect by the overlaid gate and gate dielectric layer, and low LUMO energy level of the specifi cally designed polymer. ConclusionsWe designed and synthesized a new solution-processable n-channel polymer with an extended π -conjugated backbone, without increasing the LUMO level. The obtained polymer, PNDI-TVT, had a well-controlled alternating structure consisting of a long alkyl chain-substituted NDI as an electron acceptor unit and TVT as a donor unit. The PNDI-TVT copoly mer demonstrated a remarkably high electron-carrier mobility of up to 1.8 cm 2 V − 1 s − 1 ( I on / I off = 10 6 ) and high air and bias stress stability. To the best of our knowledge, this newly developed material showed the highest n-type mobility, in combination with excellent air and operation stabilities, among the reported n-channel conjugated polymers. The superior performance of PNDI-TVT OFET was attributed to improved ππ intermolecular interactions because of the extended π -conjugation, improved crystallinity with a highly interdigitated lamellar structure owing to the extended backbone and long alkyl groups, and mixed face-on and edge-on orientation.

Layered structures of transition metal dichalcogenides stacked by van der Waals interactions are now attracting the attention of many researchers because they have fascinating electronic, optical, thermoelectric, and catalytic properties emerging at the monolayer limit. However, the commonly used methods for preparing monolayers have limitations of low yield and poor extendibility into large-area applications. Herein, we demonstrate the synthesis of large-area MoSe2 with high quality and uniformity by selenization of MoO3 via chemical vapor deposition on arbitrary substrates such as SiO2 and sapphire. The resultant monolayer was intrinsically doped, as evidenced by the formation of charged excitons under low-temperature photoluminescence analysis. A van der Waals heterostructure of MoSe2 on graphene was also demonstrated. Interestingly, the MoSe2/graphene heterostructures show strong quenching of the characteristic photoluminescence from MoSe2, indicating the rapid transfer of photogenerated charge carriers between MoSe2 and graphene. The development of highly controlled heterostructures of two-dimensional materials will further promote advances in the physics and chemistry of reduced dimensional systems and will provide novel applications in electronics and optoelectronics.