Metal oxides that absorb visible light are attractive for use as photoanodes in photoelectrosynthetic cells. However, their performance is often limited by poor charge carrier transport. We show that this problem can be addressed by using separate materials for light absorption and carrier transport. Here, we report a Ta:TiO2|BiVO4 nanowire photoanode, in which BiVO4 acts as a visible light-absorber and Ta:TiO2 acts as a high surface area electron conductor. Electrochemical and spectroscopic measurements provide experimental evidence for the type II band alignment necessary for favorable electron transfer from BiVO4 to TiO2. The host–guest nanowire architecture presented here allows for simultaneously high light absorption and carrier collection efficiency, with an onset of anodic photocurrent near 0.2 V vs RHE, and a photocurrent density of 2.1 mA/cm2 at 1.23 V vs RHE.

We report the synthesis and characterization of "bistetracene", an unconventional, linearly extended conjugated core with eight fused rings. The annellation mode of the system allows for increased stability of the conjugated system relative to linear analogues due to the increased number of Clar aromatic sextets. By attaching the appropriate solubilizing substituents, efficient molecular packing with large transfer integrals can be obtained. The electronic structure calculations suggest these large polycyclic aromatic hydrocarbons (PAHs) exhibit excellent intrinsic charge transport properties. Charge carrier mobilities as large as 6.1 cm(2) V(-1) s(-1) and current on/off ratios of 10(7) were determined experimentally for one of our compounds. Our study provides valuable insight into the design of unconventional semiconductor compounds based on higher PAHs for use in high-performance devices.

We investigated the interfacial electronic structures of indium tin oxide (ITO)/molybdenum trioxide (MoO3)/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) using in situ ultraviolet and x-ray photoemission spectroscopy to understand the origin of hole injection improvements in organic light-emitting devices (OLEDs). Inserting a MoO3 layer between ITO and NPB, the hole injection barrier was remarkably reduced. Moreover, a gap state in the band gap of NPB was found which assisted the Ohmic hole injection at the interface. The hole injection barrier lowering and Ohmic injection explain why the OLED in combination with MoO3 showed improved performance.

The field-effect hole mobility of rubicene having high ionization energy (∼5.5 eV) is 0.20 cm2 V−1 s−1 and is improved to 0.32 cm2 V−1 s−1 with PFBT SAM treatment which reduces the hole injection barrier and induces an edge-on configuration.

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...

We demonstrate the use of poly(sulfobetaine methacrylate) (PSBMA), and its pyrene-containing copolymer, as solution-processable work function reducers for inverted organic electronic devices. A notable feature of PSBMA is its orthogonal solubility relative to solvents typically employed in the processing of organic semiconductors. A strong permanent dipole moment on the sulfobetaine moiety was calculated by density functional theory. PSBMA interlayers reduced the work function of metals, graphene, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) by over 1 eV, and an ultrathin interlayer of PSBMA reduced the electron injection barrier between indium tin oxide (ITO) and C70 by 0.67 eV. As a result, the performance of organic photovoltaic devices with PSBMA interlayers is significantly improved, and enhanced electron injection is demonstrated in electron-only devices with ITO, PEDOT:PSS, and graphene electrodes. This work makes available a new class of dipole-rich, counterion-free, pH insensitive polymer interlayers with demonstrated effectiveness in inverted devices.

The most efficient architecture for achieving high donor/acceptor interfacial area in organic photovoltaics (OPVs) would employ arrays of vertically interdigitated p- and n- type semiconductor nanopillars (NPs). Such morphology could have an advantage in bulk heterojunction systems; however, precise control of the dimension morphology in a crystalline, interpenetrating architecture has not yet been realized. Here we present a simple, yet facile, crystallization technique for the growth of vertically oriented NPs utilizing a modified thermal evaporation technique that hinges on a fast deposition rate, short substrate-source distance, and ballistic mass transport. A broad range of organic semiconductor materials is beneficial from the technique to generate NP geometries. Moreover, this technique can also be generalized to various substrates, namely, graphene, PEDOT-PSS, ZnO, CuI, MoO3, and MoS2. The advantage of the NP architecture over the conventional thin film counterpart is demonstrated with an increase of power conversion efficiency of 32% in photovoltaics. This technique will advance the knowledge of organic semiconductor crystallization and create opportunities for the fabrication and processing of NPs for applications that include solar cells, charge storage devices, sensors, and vertical transistors.

The use of Rozen's reagent (HOF⋅CH3 CN) to convert polythiophenes to polymers containing thiophene-1,1-dioxide (TDO) is described. The oxidation of polythiophenes can be controlled with this potent, yet orthogonal reagent under mild conditions. The oxidation of poly(3-alkylthiophenes) proceeds at room temperature in a matter of minutes, introducing up to 60 % TDO moieties in the polymer backbone. The resulting polymers have a markedly low-lying lowest unoccupied molecular orbital (LUMO), consequently exhibiting a small bandgap. This approach demonstrates that modulating the backbone electronic structure of well-defined polymers, rather than varying the monomers, is an efficient means of tuning the electronic properties of conjugated polymers.