nonfullerene electron-accepting and electron-transporting materials is desirable to enhance the performance of OPVs. [35][36][37] Recently, several groups have reported novel nonfullerene small molecules as electron acceptors in solution-processed OPVs. [38][39][40][41][42][43][44][45][46][47][48][49] Among these materials, perylene diimide derivatives (PDIs) have widely been investigated [50][51][52][53][54][55] and have achieved power conversion effi ciencies (PCEs) as high as 6%. [52][53][54][55] However, since the high planarity and strong intermolecular interactions of PDIs lead to large-scale phase separation, one has to suppress the crystallinity of PDIs at the expense of electron mobility. [ 35,51 ] The greatest challenge in developing more effi cient nonfullerene acceptors in OPVs is the lack of good electron-transporting semiconductors that integrate solution processability with suitable energy levels and transport properties of the acceptors, and with molecular characteristics that can optimize the morphology. Naphthalene diimides (NDIs), similar to PDIs, are extensively utilized as dye materials, providing a unique variability in structure modifi cation and a widely tunable absorption. [56][57][58][59][60] However, compared with PDI-based small molecules, NDI-based small molecules have not been extensively studied as acceptors in OPVs, with the exception of the NDI-thiophene oligomers reported by Sauvé and co-workers [ 61,62 ] and Jenekhe and co-workers, [ 63,64 ] which showed highest PCEs of 1.5%. NDI is a versatile electron-defi cient building block that has been employed as a high electron mobility semiconductor. [ 65 ] Here, we designed and synthesized a novel dimer of NDI (BiNDI) using a vinyl linker ( Figure 1 A), which can extend the conjugation length, planarize the molecular backbone, and enhance the intermolecular π-π stacking. BiNDI exhibited an excellent electron transport property with a highest electron mobility of 0.365 cm 2 V −1 s −1 . OPVs by using BiNDI as the acceptor showed a highest PCE of 2.41%, which is the best result for NDI-based small molecular acceptors. Results and Discussion Material Synthesis and CharacterizationAs shown in Figure 1 A, BiNDI was synthesized by Stille coupling of monobromo-NDI and trans-1,2-bis(tributylstannyl) ethane in the presence of Pd(PPh 3 ) 4 . The reaction product is A novel naphthalene diimide (NDI)-based small molecule (BiNDI) is designed and synthesized by linking two NDI monomers via a vinyl donor moiety. The electronic structure of BiNDI is carefully investigated by ultraviolet photoelectron spectroscopy (UPS). Density functional theory (DFT) sheds further light on the molecular confi guration and energy level distribution. Thin fi lm transistors (TFT) based on BiNDI show a highest electron mobility of 0.365 cm 2 V −1 s −1 in ambient atmosphere. Organic photovoltaics (OPVs) by using BiNDI as the acceptor show a highest power conversion effi cency (PCE) of 2.41%, which is the best result for NDI-based small molecular acceptors. Transmission el...

Herein, this study investigates the impact of branching-point-extended alkyl chains on the charge transport properties of three ultrahigh n-type mobility conjugated polymers. Using grazing incidence wide-angle X-ray scattering, analysis of the crystallinity of the series shows that while π-π interactions are increased for all three polymers as expected, the impact of the side-chain engineering on polymer backbone crystallinity is unique to each polymer and correlates to the observed changes in charge transport. With the three polymers exhibiting n-type mobilities between 0.63 and 1.04 cm 2 V −1 s −1 , these results ratify that the indolonaphthyridine building block has an unprecedented intrinsic ability to furnish high-performance n-type organic semiconductors.

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