Multiple exciton generation

Nozik AJ (2008) Multiple exciton generation in semiconductor quantum dots. Chem Phys Lett 457 3-11... 

New Solar Cells Quantum Dot (QD) Structures and Multiple Exciton Generation (MEG)... 

The QD s absorption can be used directly or it can be used to get multiple exciton generation. The latter has recently been shown in suitably chosen QDs, such as PbSe and Si.36,37 This discovery allows for the potential of a variety of devices employing both upconversion and downconversion. 

Luque, A. Marti, A. Nozik, A. J. 2007. Quantum dots Multiple exciton generation and intermediate bands. MRS Bull. 32 236-241. 

At present the IV-VI series of semiconducting materials comprises a number of the most promising materials for IR applications [1-4]. An interest in these materials is primarily because they are narrow band gap semiconductors and therefore have the potential to be employed in devices as optically active components in the near-infrared (NIR) and infrared (IR) spectral region and are hence beneficial to applications for solar cells, detectors, telecommunications relays, etc. The interest in the IV-VI materials has also grown in recent years because of the observation that they are thought to demonstrate efficient multiple exciton generation (MEG) [3,5-7]. This has implications for the efficiencies of solar cells and other applications based on these materials, especially as it provides a means by which the Shockley/Queisser efficiency limit may be overcome. 

High conversion efficiency via multiple exciton generation in quantum dots... 

Ellingson R. J., Beard M. C., Johnson J. C., Yu P., Micic 0.1., Nozik A. J., Shabaev A. and Efros A. L. (2005), Highly efficient multiple exciton generation in colloidal PbSe and PbS quantum dots , Nano Lett. 5, 865-871. 

The leitmotifs of these devices include bespoke dye sensitisers, space-quantised nanoscale structures that enable hot carrier or multiple exciton generation, molecular and solid-state junction architectures that lead to efficient exciton dissociation and charge separation, and charge collection by percolation through porous or mesoscale phases. Another common theme underlying the devices discussed in this book is the... 

There are several emerging areas of nanophotonics, which include plasmonics, multiple exciton generation, photonic crystals, and upconversion. While these concepts have been applied to the design of solar cells, the exploration of these concepts in the context of water photoelectrolysis devices is limited. It is therefore of interest to consider the ways in which advances in nanophotonics could influence the direction of future work in water photoelectrolysis. This section emphasizes developments in plasmonics that may be useful if successfully applied to water photoelectrolysis. 

The initial intent of this chapter was to provide a broad overview and a critical assessment of various trends in the theory of effectively unpaired electrons. In the process of preparing the manuscripts some accents were shifted, and we would unavoidably restrict ourselves to a narrow set of issues and examples for discussion. For instance, we only slightly touched on the electron unpairing analysis in stmctures with a spatial separation of molecular subunits. These are bichromophore systems, molecular dimers and complexes, radical and ion-radical pairs, etc. The recent papers [77, 78, 125] are dedicated just to these problems. Besides, many interesting systems, e.g., semiconductor quantum dots, fell beyond the scope of this review. Indeed, many-electron aspects of the multiple exciton generation (MEG) in quantum dots are closely related to the EUE theory, but only circumstantial evidence about EUE effects in MEG can be found in the current literature [127, 128]. 

The nontraditional approaches in photoelectrochemistry encompass systems and effects where the conversion efficiency exceeds that of the single junction Shockley-Queisser limit (defect level absorbers, multiple exciton generation, singlet fission). In a second approach, the use of hot electrons for initiating electrochemical reactions which otherwise would necessitate large overvoltages is attempted. Besides the direct use of non-thermalized hot electrons from the absorber surface [107], recently, contributions from the decay of surface plasmons have been investigated, too [108, 109]. The third approach is based on... 

Nozik AJ, Beard MC, Luther JM et al (2010) Semiconductor quantum dots and quantum dot arrays and applications of multiple exciton generation to third-generation photovoltaic solar cells. Chem Rev 110 6873-6890... 

Figure 11.25 Quantum yield vs absorbed photon energy (normalized to the bandgap) of a nanocrystal for various multiple exciton generation (MEG). Details concerning the labeling of the curves are given in the text (after [180]).

The formation of multiple electron-hole pairs (excitons) are identical to multiple exciton generation, that is, ehpm = /meg- b carriers are formed upon dissociation of the excitons. The generation rate of excitons /tmeg competes with the radiationless deactivation of an electron down to the bottom of the conduction band The ratio between these two rates is given by the factor P which is related to tj EG by [180]... 

Allan, G., Delerue, C. (2008). Influence of electronic structure and multiexciton spectral density on multiple-exciton generation in semiconductor nanocrystals Tight-binding calculations. Physical Review B, 77,125340(10). 

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