Solar cells nanocrystal

Robel, I., Subramanian, V., Kuno, M. and Kamat, P. V. (2006) Quantum dot solar cells. Harvesting light energy with CdSe nanocrystals molecularly linked to mesoscopic Ti02 films. /. Am. Chem. Soc., 128, 2385-2393. 

Colloidal semiconductor nanocrystals are attracting growing attention as the building blocks for inexpensive, large-area, solution-processed solar cells. The advantages here are the scalable and controlled synthesis, an ability to be processed in solution, the broadband absorption, and the superior transport properties of traditional photovoltaic semiconductors. Solar cells that rely exclusively on colloidal nanocrystals have been anticipated theoretically58 and... 

Gur, I. Fromer, N. A. Geier, M. L. Alivisatos, A. P. 2005. Air-stable all-inorganic nanocrystal solar cells processed from solution. Science 310 462—465. 

Nanocrystals and nanowires are utilized in a new generation of solar collectors (a nanometer is one billionth of a meter). In conventional solar cells, at the P-N junction one photon splits one electron from its "hole companion" as it travels to the electron-capturing electrode. If solar collectors are made of semiconducting nanocrystals that disperse the light, according to TU Delft s professor Laurens Siebbeles, an avalanche effect results and one photon can release two or three electrons, because this effect maximizes photon absorption while minimizing electron-hole recombination. This effect of the photon-scattering nanoparticles substantially increases cell efficiency. 

Several polymer/polyelectrolyte-nanocrystal hybrid devices have been fabricated seeking to exploit the electro and photoluminescent properties of such material [179-188]. Device fabrication in all these cases is by low-cost self-assembly based techniques. These devices utilize thin films of these hybrids obtained either by multilayer deposition or drop/spin casting methods. Thus, solar cells have been made from poly(2-hexylthiophene)-CdSe nanorod multilayers, lasers from drop cast films of CdSe-titania composites and an infrared emitter from multilayers... 

Wang P., Zakeeruddin S. M., Humphry-Baker R., Moser J. E. and Gratzel M. (2003a), Molecular-scale interface engineering of TiOi nanocrystals improving the efficiency and stability of dye-sensitized solar cells , Adv. Mat. 15, 2101-2103. 

CdSe nanocrystal based solar cells were substantially improved by Sun et al a twofold increase in the EQE was achieved for MDMO-PPV based blends by application of CdSe nanotetrapods instead of nanorods [254]. The tetrapods, due to their shape, induced better directed electron transport normal to the film plane, yielding overall power conversion efficiencies of 1.8%. The current-voltage characteristics of this device are displayed in Pig. 57. 

Several interesting new concepts for the design of CdSe nanocrystal based polymer solar cells have been introduced recently. Snaith et al. have infiltrated CdSe nanocrystals into polymer brushes and demonstrated EQEs of up to 50% [256]. In this case the poly(triphenylamine acrylate) (PTPAA) chains were directly grown from the substrate by a surface-initiated polymerization on tethered initiator sites (Fig. 58). The authors pronounced the wide applicability of this method for the design of nanocrystal-polymer functional blends [256]. 

One extensively studied material system among the nanocrystal-polymer blends is zinc oxide (ZnO) in combination with MDMO-PPV or P3HT [273-282]. Beek et al. presented the first polymer solar cells containing ZnO nanoparticles, reaching power conversion efficiencies of 1.6% [273]. In this case the nanoparticles were prepared separately and then intermixed with MDMO-PPV in solution. Shortly after this study the Janssen group presented another route to ZnO-polymer hybrid solar cells by forming the nanocrystals in situ inside the film by applying a precursor [274]. Here, diethylzinc served as the precursor and was spin cast in blends with MDMO-PPV. Process-... 

Huynh WU, Dittmer JJ, Libby WC, Whiting GL, Alivisato AP (2003) Controlling the morphology of nanocrystal-polymer composites for solar cells. Adv Funct Mater 13 73... 

Gunes S, Neugebauer H, Sariciftci NS, Roither J, Kovalenko M, Pillwein G, Heiss W (2006) Hybrid solar cells using HgTe nanocrystals and nanoporous Ti02 electrodes. Adv Eunct Mater 16 1095... 

Nanomaterials energy and applications As nanocrystals and nanotubes are better understood, it becomes possible to rationally design nano-structured materials for specific purposes. This area includes both chemical synthesis and physical properties of nanostructured materials incorporating fullerenes, organic conductive polymers, and inorganic nanostructures. A central goal is composite materials for solar energy utilization—new types of solar cells. 

A hybrid nanosystem which consists of semiconductor nanoparticles and organic dye J-aggregate may be self-assembled in RMs (Fig. 5) [4], In this structure, the dye adsorbed to the nanoparticle surface operates as spectral sensitizer and nanocrystal size stabilizer simultaneously. The hybrid nanosystem of this kind may be a key element of solar cells. 

In bulk (or dispersed) heterojunctions, nanocrystals are blended into the polymer to create a heterogeneous composite with a high interface surface area. In this hybrid solar cell concept, photo induced charge separation is favored between high electron affinity inorganic semiconductors and relatively low ionization potential polymer. The maximum power conversion efficiency has reached 2.8 % under AM 1.5 illumination condition by using the composite of tetrapods of CdSe nanocrystals and MDMO-PPV [4], while the PCE of the device based on the composite of CdTe nanorods and MEH-PPV is only 0.052 % in similar conditions [5]. 

S. Kumar and G.D. Scholes, Colloidal nanocrystal solar cells, Microchim. Acta, 160, 315-325 (2008). 

---