A conjugated small molecule containing a benzodithiophene unit shows high performance in bulk heterojunction (BHJ) solar cells. Using the simple solution spinning process, a high PCE is achieved by employing this molecule as the donor in BHJ solar cells.

The nonlinear optical properties of graphene oxide (GO) were investigated at 532 nm in nanosecond and picosecond regimes. Results show that two-photon absorption dominates nonlinear absorption process of GO in the case of picosecond pulses, while excited state nonlinearities play an important role in the case of nanosecond pulses. Additionally, we compared nonlinear optical properties of three different dimensional carbon-based materials (two-dimensional graphene, one-dimensional carbon nanotube, and zero-dimensional fullerene) in nanosecond and picosecond regimes, respectively. The nonlinear mechanism of GO is distinctly different from nonlinear scattering of carbon nanotube and excited state nonlinearity of fullerene.

Organic solar cells (OSCs) have attracted signifi cant attention as a clean and competitive renewable energy source due to their attractive features such as low-cost, light weight, solution processability and high mechanical fl exibility. [1][2][3][4] Benchmark power conversion effi ciencies (PCEs) of 10% or higher have been predicted if a suitable low bandgap donor material can be designed and implemented. [ 5 ] More recently, bulk heterojunction (BHJ) OSCs using solution-processed small molecules as the donor have attracted great attention. [6][7][8] This long-time but recently increased interest lies in the fact that solutionprocessed small molecule based OSCs have numerous advantages, such as relatively simple synthesis and purifi cation methods, monodispersity and well defi ned structures, high open circuit voltage and charge carrier mobilities, and better batch-to-batch reproducibility. [6][7][8] However, solution-processed small molecule OSCs have not met such high expectations as those of their polymeric counterparts due to their limited PCEs. In most cases, small molecule devices using solution processing always seem to have poorer fi lm quality than that of their polymeric counterparts in BHJ OSCs. [ 6 , 7 ] It is thus expected that better PCE could be achieved if the intrinsic poor fi lm quality and morphology in BHJ architecture could be improved. However, in order to achieve this, careful molecule design has to be carried out to address many factors simultaneously, including the material's solar light absorption associated with its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) positions, mobility, fi lm forming quality, electronic band structure and morphology compatibility with the acceptors, and so on. Indeed, several families of solution processed small molecules, such as oligothiophenes, [ 9 ] triarylamines, [ 10 , 11 ] diketopyrrolopyrroles (DPP), [ 12 ] squaraines, [ 13 , 14 ] merocyanine, [ 15 ] and dipyrromethene boron difl uoride (BODIPY) [ 16 ] derivatives, have offered great promise in this direction. Although still lower than the PCE of their polymeric counterparts ( ∼ 6-8%), [17][18][19][20][21] the highest published PCE of 4.4% for solution-processed small molecule/fullerene derivative based BHJ OSCs was recently achieved by a University of California Santa Barbara group using a DPP-thiophene derivative. [ 12 ] Push-pull chromophores involving electron-donating and electron-withdrawing groups have been widely investigated for OSC molecules. [ 8 ] This type of molecular architecture can lower the material bandgap and extend the absorption spectrum toward longer wavelengths, and at the same time, the HOMO and LUMO levels can be tuned effectively. [ 11 , 22 ] Oligothiophenes with well defi ned structures possess highly delocalized π -electrons along the molecular backbone and are well known as one of the most effective hole-transporting materials. Oligothiophenes with a push-pull structure have been widely investigated in solution processed ...

Metasurfaces utilizing engineered metallic nanostructures have recently emerged as an important means to manipulate the propagation of light waves in a prescribed manner. However, conventional metallic metasurfaces mainly efficiently work in the visible and near-infrared regime, and lack sufficient tunability. In this work, combining the pronounced plasmonic resonance of patterned graphene structures with a subwavelength-thick optical cavity, we propose and demonstrate novel graphene metasurfaces that manifest the potential to dynamically control the phase and amplitude of infrared light with very high efficiency. It is shown that the phase of the infrared light reflected from a simple graphene ribbon metasurface can span over almost the entire 2π range by changing the width of the graphene ribbons, while the amplitude of the reflection can be maintained at high values without significant variations. We successfully realize anomalous reflection, reflective focusing lenses, and non-diffracting Airy beams based on graphene metasurfaces. Our results open up a new paradigm of highly integrated photonic platforms for dynamic beam shaping and adaptive optics in the crucial infrared wavelength range.

Coding acoustic metasurfaces can combine simple logical bits to acquire sophisticated functions in wave control. The acoustic logical bits can achieve a phase difference of exactly π and a perfect match of the amplitudes for the transmitted waves. By programming the coding sequences, acoustic metasurfaces with various functions, including creating peculiar antenna patterns and waves focusing, have been demonstrated.