Charge separation at disordered semiconductor heterojunctions from random walk numerical simulations

Mandujano-Ramírez, Humberto J.; Gonzalez-Vazquez, J. P.; Oskam, Gerko; Dittrich, Thomas; García-Belmonte, Germà; Mora‐Seró, Iván; Bisquert, Juan; Anta, Juan A.

doi:10.1039/c3cp54237h

Cited by 10 publications

(9 citation statements)

References 71 publications

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“…These devices are photoelectrochemical cells (PECs) [40,87] with photoactive cathodes consisting of -type semiconducting materials and include -type dye-sensitized solar cells ( -DSCs) ( Figure 6) [242,243,247,248,264] and tandem DSCs (t-DSCs) (Figure 7) [ [265][266][267][268][269] cells of photoelectrolysis for nonfossil fuels production, namely, molecular H 2 in the process of water splitting (Figure 8) [270][271][272][273][274][275][276][277][278][279][280][281] and for carbon dioxide redox reduction (Figure 9) . The initial charge separation produced as a consequence of light absorption [312,313] can occur either directly on the -type semiconductor (Figure 9) or on the electrically connected sensitizer which accomplishes successively the transfer of charge according to the vectoriality imparted by the relative positions of the energy levels of the electronic states involved and by the kinetics of the possible redox reactions (Figures 6-8).…”

Section: Part Ii: -Type Semiconductorsmentioning

confidence: 99%

Nanostructured Semiconductor Materials for Dye-Sensitized Solar Cells

Cavallo

Pascasio

Latini

et al. 2017

Journal of Nanomaterials

108

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Since O’Regan and Grätzel’s first report in 1991, dye-sensitized solar cells (DSSCs) appeared immediately as a promising low-cost photovoltaic technology. In fact, though being far less efficient than conventional silicon-based photovoltaics (being the maximum, lab scale prototype reported efficiency around 13%), the simple design of the device and the absence of the strict and expensive manufacturing processes needed for conventional photovoltaics make them attractive in small-power applications especially in low-light conditions, where they outperform their silicon counterparts. Nanomaterials are at the very heart of DSSC, as the success of its design is due to the use of nanostructures at both the anode and the cathode. In this review, we present the state of the art for bothn-type andp-type semiconductors used in the photoelectrodes of DSSCs, showing the evolution of the materials during the 25 years of history of this kind of devices. In the case ofp-type semiconductors, also some other energy conversion applications are touched upon.

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Section: Part Ii: -Type Semiconductorsmentioning

confidence: 99%

Nanostructured Semiconductor Materials for Dye-Sensitized Solar Cells

Cavallo

Pascasio

Latini

et al. 2017

Journal of Nanomaterials

108

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“…The molar volumes of g-but, DMAc, DMSO and IL were input into eqn (8). DMAc has a w IL | min value of 0.09 (the less accurate, linearized eqn (6) gives 0.12 and the value calculated from the fit in Fig. 2 is 0.06), w IL | min DMSO is 0.056 and g-but is 0.06.…”

Section: Use Of the Random Walk Modelmentioning

confidence: 99%

“…There has been a wealth of research into random walks in many fields. 1,2 Within chemistry and materials science, random walks have been applied to polymer absorption, 3 copolymer structure, 4 electron traps in semiconductors, 5,6 quantum mechanical paths, 2,7 phonons in liquids, 8 phospholid motion in cell membranes, 9 diffusion in zeolites, 10 motion of insulin granules in cells, 11 intramolecular migration of chemical species along oligomers, 12 rotaxanes diffusing along polymers, 13 and modelling of polymer motion. 14 The most extensive use has been the that of a self-avoiding random walk to generate polymer conformations.…”

Section: Introductionmentioning

confidence: 99%

Combining random walk and regression models to understand solvation in multi-component solvent systems

Gale

Johns

Wirawan

et al. 2017

Phys. Chem. Chem. Phys.

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Polysaccharides, such as cellulose, are often processed by dissolution in solvent mixtures, e.g. an ionic liquid (IL) combined with a dipolar aprotic co-solvent (CS) that the polymer does not dissolve in. A multi-walker, discrete-time, discrete-space 1-dimensional random walk can be applied to model solvation of a polymer in a multi-component solvent mixture. The number of IL pairs in a solvent mixture and the number of solvent shells formable, x, is associated with n, the model time-step, and N, the number of random walkers. The mean number of distinct sites visited is proportional to the amount of polymer soluble in a solution. By also fitting a polynomial regression model to the data, we can associate the random walk terms with chemical interactions between components and probe where the system deviates from a 1-D random walk. The 'frustration' between solvents shells is given as ln x in the random walk model and as a negative IL:IL interaction term in the regression model. This frustration appears in regime II of the random walk model (high volume fractions of IL) where walkers interfere with each other, and the system tends to its limiting behaviour. In the low concentration regime, (regime I) the solvent shells do not interact, and the system depends only on IL and CS terms. In both models (and both regimes), the system is almost entirely controlled by the volume available to solvation shells, and thus is a counting/space-filling problem, where the molar volume of the CS is important. Small deviations are observed when there is an IL-CS interaction. The use of two models, built on separate approaches, confirm these findings, demonstrating that this is a real effect and offering a route to identifying such systems. Specifically, the majority of CSs - such as dimethylformide - follow the random walk model, whilst 1-methylimidazole, dimethyl sulfoxide, 1,3-dimethyl-2-imidazolidinone and tetramethylurea offer a CS-mediated improvement and propylene carbonate results in a CS-mediated hindrance. It is shown here that systems, which are very complex at a molecular level, may, nonetheless, be effectively modelled as a simple random walk in phase-space. The 1-D random walk model allows prediction of the ability of solvent mixtures to dissolve cellulose based on only two dissolution measurements (one in neat IL) and molar volume.

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“…Because the photovoltage is entirely de-coupled from solid-liquid charge transfer, it allows direct measurement of solid-solid junction potentials. Thomas Dittrich's group has used SPS extensively over the past decade on nanocrystal [198][199][200], molecular [201][202][203], and thin film [204] photovoltaics. However, as shown in the following example, SPS is also well suited for the characterization of nanostructured photocatalysts, where it can provide a quantitative understanding of charge transfer at solid-solid and solid-molecule contacts [189].…”

Section: Measuring Photovoltage In Nanoscale Photocatalystsmentioning

confidence: 99%

Nanoscale Effects in Water Splitting Photocatalysis

Osterloh

2015

Topics in Current Chemistry

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From a conceptual standpoint, the water photoelectrolysis reaction is the simplest way to convert solar energy into fuel. It is widely believed that nanostructured photocatalysts can improve the efficiency of the process and lower the costs. Indeed, nanostructured light absorbers have several advantages over traditional materials. This includes shorter charge transport pathways and larger redox active surface areas. It is also possible to adjust the energetics of small particles via the quantum size effect or with adsorbed ions. At the same time, nanostructured absorbers have significant disadvantages over conventional ones. The larger surface area promotes defect recombination and reduces the photovoltage that can be drawn from the absorber. The smaller size of the particles also makes electron-hole separation more difficult to achieve. This chapter discusses these issues using selected examples from the literature and from the laboratory of the author.

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Charge separation at disordered semiconductor heterojunctions from random walk numerical simulations

Cited by 10 publications

References 71 publications

Nanostructured Semiconductor Materials for Dye-Sensitized Solar Cells

Nanostructured Semiconductor Materials for Dye-Sensitized Solar Cells

Combining random walk and regression models to understand solvation in multi-component solvent systems

Nanoscale Effects in Water Splitting Photocatalysis

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