Solar cells quantum efficiency

Hyun et al. [345] prepared PbS Q-dots in a suspension and tethered them to Ti02 nanoparticles with a bifunctional thiol-carboxyl linker molecule. Strong size dependence due to quantum confinement was inferred from cyclic voltammetry measurements, for the electron affinity and ionization potential of the attached Q-dots. On the basis of the measured energy levels, the authors claimed that pho-toexcited electrons should transfer efficiently from PbS into T1O2 only for dot diameters below 4.3 nm. Continuous-wave fluorescence spectra and fluorescence transients of the PbS/Ti02 assembly were consistent with electron transfer from small Q-dots. The measured charge transfer time was surprisingly slow ( 100 ns). Implications of this fact for future photovoltaics were discussed, while initial results from as-fabricated sensitized solar cells were presented. 

SN)X can act as an efficient barrier electrode in ZnS junctions, increasing the quantum efficiency of the blue emission by a factor of 100 over gold.14 It can also be used to increase the efficiency of GaAs solar cells by up to 35%. Metal ions interact more strongly with a poly(sulfur nitride) surface than with other metal electrodes. This property has stimulated investigations of possible applications of (SN)X as an electrode material. 

Muffler, H-J. Bar, M. Lauermann, I. Rahne, K. Schroder, M. Lux-Steiner, M. C. Fischer, C.-H. Niesen, T. P. Karg, F. 2006. Colloid attachment by ILGAR-layers Creating fluorescing layers to increase quantum efficiency of solar cells. Sol. Energy Mater. Sol. Cells 90 3143-3150. 

Polycrystalline GaN UV detectors have been realized with 15% quantum efficiency [4], This is about 1 /4 of the quantum efficiency obtained by crystalline devices. Available at a fixed price, however, their increased detection range may well compensate their lack in sensitivity. Furthermore, new semiconductor materials with a matching band gap appear as promising candidates for UV detection if the presumption of the crystallinity is given up. Titanium dioxide, zinc sulfide and zinc oxide have to be mentioned. The opto-electronic properties and also low-cost production processes for these compound semiconductors have already been investigated to some extent for solar cell applications [5]. 

S. Kolodinski, J.H. Werner, T. Wittchen, H.J. Queisser, Quantum efficiencies exceeding unity due to impact ionization in silicon solar cells, Appl. Phys. Lett. 63 (1993) 2405-2407. 

The quantum efficiency for solid-state devices, e.g. solar cells, is always below unity. For n-type silicon electrodes anodized in aqueous or non-aqueous HF electrolytes, quantum efficiencies above unity are observed because one or more electrons are injected into the electrode when a photogenerated hole enters the electrolyte. Note that energy conservation is not violated, due to the enthalpy of the electrochemical dissolution reaction of the electrode. 

Rau U (2007) Reciprocity relation between photovoltaic quantum efficiency and electroluminescent emission of solar cells. Phys Rev B 76 085303... 

Another way that nanotechnology may impact solar cells is the use of quantum dots instead of silicon. Quantum dots, which are nanoscale semiconductor crystals, could significantly lower the cost of photovoltaic cells. In 2006, Victor Klimov of Los Alamos National Laboratory in New Mexico demonstrated that quantum dots have the capability to react to light and store energy more efficiently than silicon. Although scientists are years away from actually manufacturing usable quantum dot solar cells on a commercial scale, the technology has been established. 

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