Concomitant development of [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) aggregation and poly(3-hexylthiophene) (P3HT) crystallization in bulk heterojunction (BHJ) thin-film (ca. 85 nm) solar cells has been revealed using simultaneous grazing-incidence small-/wide-angle X-ray scattering (GISAXS/GIWAXS). With enhanced time and spatial resolutions (5 s/frame; minimum q ≈ 0.004 Å(-1)), synchrotron GISAXS has captured in detail the fast growth in size of PCBM aggregates from 7 to 18 nm within 100 s of annealing at 150 °C. Simultaneously observed is the enhanced crystallization of P3HT into lamellae oriented mainly perpendicular but also parallel to the substrate. An Avrami analysis of the observed structural evolution indicates that the faster PCBM aggregation follows a diffusion-controlled growth process (confined by P3HT segmental motion), whereas the slower development of crystalline P3HT nanograins is characterized by constant nucleation rate (determined by the degree of supercooling and PCBM demixing). These two competing kinetics result in local phase separation with space-filling PCBM and P3HT nanodomains less than 20 nm in size when annealing temperature is kept below 180 °C. Accompanying the morphological development is the synchronized increase in electron and hole mobilities of the BHJ thin-film solar cells, revealing the sensitivity of the carrier transport of the device on the structural features of PCBM and P3HT nanodomains. Optimized structural parameters, including the aggregate size and mean spacing of the PCBM aggregates, are quantitatively correlated to the device performance; a comprehensive network structure of the optimized BHJ thin film is presented.

We consider a head-on collision between two solitary waves on the surface of an inviscid homogeneous fluid. A perturbation method which in principle can generate an asymptotic series of all orders, is used to calculate the effects of the collision. We find that the waves emerging from (i.e. long after) the collision preserve their original identities to the third order of accuracy we have calculated. However a collision does leave imprints on the colliding waves with phase shifts and shedding of secondary waves. Each secondary wave group trails behind its primary, a solitary wave. The amplitude of the wave group diminishes in time because of dispersion. We have also calculated the maximum run-up amplitude of two colliding waves. The result checks with existing experiments.

Perspective on recent improvements in experiment and theory towards realizing lithium metal electrodes with liquid electrolytes.

We have developed an improved small-angle X-ray scattering (SAXS) model and analysis methodology to quantitatively evaluate the nanostructures of a blend system. This method has been applied to resolve the various structures of self-organized poly(3-hexylthiophene)/C61-butyric acid methyl ester (P3HT/PCBM) thin active layer in a solar cell from the studies of both grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence X-ray diffraction (GIXRD). Tuning the various length scales of PCBM-related structures by a different annealing process can provide a flexible approach and better understanding to enhance the power conversion of the P3HT/PCBM solar cell. The quantitative structural characterization by this method includes (1) the mean size, volume fraction, and size distribution of aggregated PCBM clusters, (2) the specific interface area between PCBM and P3HT, (3) the local cluster agglomeration, and (4) the correlation length of the PCBM molecular network within the P3HT phase. The above terms are correlated well with the device performance. The various structural evolutions and transformations (growth and dissolution) between PCBM and P3HT with the variation of annealing history are demonstrated here. This work established a useful SAXS approach to present insight into the modeling of the morphology of P3HT/PCBM film. In situ GISAXS measurements were also conducted to provide informative details of thermal behavior and temporal evolution of PCBM-related structures during phase separation. The results of this investigation significantly extend the current knowledge of the relationship of bulk heterojunction morphology to device performance.

The development of conjugated polymers for use in organic optoelectronic devices has been an area of extensive investigation. Heterojunction polymer solar cells have been reported utilizing poly( p-phenylenevinylene) derivatives, [1] poly (3-alkylthiophene), [2] or low-bandgap polymers [3] as donors and fullerene derivatives as acceptors. Notably, poly(3-hexylthiophene)/[6,6]-phenyl-C 61 -butyric acid methyl ester (P3HT/PCBM) bulk heterojunctions display power conversion efficiencies of up ca. 5%.[4] The improved power conversion efficiencies of these devices results from the use of thermal annealing [4a] and solvent annealing [4b] processes, which enhance the film morphology relative to that of the as-cast film. The resulting improvement in performance of these systems have been attributed to (i) self-organization of P3HT into a crystalline structure exhibiting enhanced absorption and high hole mobility/transport, and (ii) diffusion of PCBM molecules into PCBM-rich clusters to form large PCBM clusters. The nanostructured phase separation of P3HT/PCBM creates percolated pathways for transporting the holes and electrons to their respective electrodes. Therefore, the performance of these heterojunction solar cells depends critically on the morphology of their active layers. Grazing-incidence X-ray diffraction (GIXRD) has been used previously to establish the dimensions of P3HT crystallites in P3HT/PCBM bulk heterojunction polymer solar cells; [5] morphological studies have also been undertaken using transmission electron microscopy (TEM) and electron diffraction.[6] The morphology of P3HT/PCBM bulk heterojunction solar cells after solvent annealing can also be analyzed using atomic force microscopy (AFM), [7] and scanning transmission X-ray microscopy (STXM) [8] has been applied to study the phase separation of PCBM on the order of several hundred nanometers, with a resolution limit of several tens of nanometers. These analytical tools, however, provide only a local view of the morphology; they cannot represent the full morphology of the active layer in the devices. Small-angle X-ray scattering (SAXS), which utilizes the elastic scattering of X-rays to probe nanostructures having sizes ranging from 1 to 100 nm, provides statistically averaged morphologies of analyzed samples.[9] For polymer/fullerene bulk heterojunction solar cells, SAXS can provide global information regarding the internal structure of the dispersion of fullerene units within the polymer matrix much more effectively than can TEM or the other analysis techniques.In this present study, we simultaneously applied grazingincidence small-angle X-ray scattering (GISAXS) and wideangle X-ray diffraction (GIWAXD) to study the morphology of P3HT/PCBM bulk heterojunction solar cells after their thermal annealing. Utilizing this approach, we could therefore elucidate the relationship between the relative length scales of the PCBM clusters and P3HT crystallites and the devices' performance. Figure 1a displays the GIWAXD profiles of several P3HT/ PCBM film...

From dictating the redox potential of electrolyte solvents to shaping the stability of solid-electrolyte interfaces, solvation plays a critical role in the electrochemistry of electrolytes.

A continuum theory for spherical electrostatic probes in a slightly ionized plasma is developed. The density of the plasma is taken to be sufficiently high such that both ions and electrons suffer numerous collisions with the neutrals before being collected by an absorbing probe. A general discussion of probes at an arbitrary potential is given. It is found that for very negative probe potentials the sheath thickness can be comparable to the probe radius. Two explicit forms of current-voltage characteristics are given; one for very negative probes, the other for probes at nearly plasma potential. Both of these are based on the assumption that the probe radius is large compared with the Debye length. Numerical computation is also given for negative probes of a wider range of probe sizes.

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