Carrier multiplication, efficient

Schaller R. D., Petruska M. A. and KUmov V. 1. (2005b), Effect of electronic structure on carrier multiplication efficiency comparative study of PbSe and CdSe nanocrystals , Appl. Phys. Lett. 87,253102-253104. 

The carrier multiplication (CM) process generated as a result of a single photon absorption in a spherical quantum dot (QD) is explained as due to multiple,virtual band-to-band electron-photon quantum transitions. Only the electron-photon interaction is used as a perturbation without the participation of the Coulomb electron-electron interaction. The creation of an odd number of electron-hole (e-h) pairs in our model is characterized by the Lorentzian-type peaks, whereas the creation of an even number of e-h pairs is accompanied by the creation of one real photon in the frame of combinational Raman scattering process. Its absorption band is smooth and forms an absorption background without peak structure. It can explain the existence of a threshold on the frequency dependence of the carrier multiplication efficiency in the region corresponding to the creation of two e-h pairs. 

Hanna MC, Nozik AJ (2006) Solar conversion efficiency of photovoltaic and photoelectrolysis cells with carrier multiplication absorbers. J Appl Phys 100 074510 (8 pages)... 

R. Schaller, V. Klimov, High efficiency carrier multiplication in PbSe nanocrystals Implications for solar energy conversion, Phys. Rev. Lett. 92 (2004) 186601. 

MEG PV device is 44.4% for bandgap Eg = 0.7 eV, where = 6. This is similar to the value reported by de Vos and Desoete (1998) for a blackbody-illuminated PV device with maximum carrier multiplication. It is interesting to note that a high efficiency of -42% is still obtained with a multiplication of only 2 (curve labelled M2), which is 94% of the absolute maximum. This means that high multiplication values (>2) are not essential for substantially increasing the efficiencies of single-gap PV devices having carrier multiplication absorbers. 

Brendel R., Werner J. H. and Queisser H. J. (1996), Thermodynamic efficiency limits for semicondnctor solar cells with carrier multiplication , Sol. Energy Mat. Sol. Cells 41-2, 419-425. 

Schaller R. D., Agranovich V. M. and Klimov V. I. (2005a), High-efficiency carrier multiplication through direct photogeneration of multiexcitons via virtual single-exciton states , Nat. Phys. 1, 189-194. 

Spirkl W. and Ries H. (1995), Lnminescence and efficiency of an ideal photovoltaic cell with charge carrier multiplication , Phys. Rev. B 52, 11319-11325. 

NCs contain approximately 100-10,000 atoms. Because of the strong spatial confinement of electronic wavefunctions and reduced electronic screening, the effects of carrier-carrier Coulomb interactions are greatly enhanced in NCs compared with those in bulk materials. These interactions open a highly efficient decay channel via Auger recombination and just such a strong carrier-carrier interaction in NCs is responsible for carrier multiplication (61)-(63). 

TTS exists also in single photon avalanche photodiodes (SPADs). The source of TTS in SPADs is the different depth at which the photons are absorbed, and the nonuniformity of the avalanche multiplication efficiency. This results in differing delays in the build-up of the carrier avalanche and in different avalanche transit times. Consequently the TTS depends on the wavelength and the voltage. Moreover, if a passive quenching circuit is used, the reverse voltage may not have completely recovered from the breakdown of the previous photon. The result is an increase of the TTS width or a shift of the TTS with the count rate. 

The proposed model of the carrier multiplication process in quantum dots permits to explain a possibility to create with considerable probability three electron-hole pairs. It shows the way to the two steps with creation of four and five e-h pairs. It can explain the existence of the threshold on the frequency dependence of the CM quantum efficiency, when two pairs and a Raman scattered photon are created. 

Schaller RD, Klimov VI (2004) High Efficiency Carrier Multiplication in PbSe Nanocrystals Implications for Solar Energy Conversion. Phys Rev Lett 92 186601... 

The development of high quality semiconductor systems where quantum eon-finement occurs, manifested in the creation of discrete, atom-like , electronie states rather than continuous bulk states, has boosted the interest of the PV research community in the implementation of solar cell geometries based on nanostructures. Particularly, colloidal quantum dots have emerged as potential candidates for developing inexpensive and highly efficiency concepts, including tandem solar cells,hot carrier solar cells and cells based on carrier multiplication. " ... 

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