Solar cells illuminated

Figure 15-31. l/V characteristics of a large area plastic solar cell ( illuminated with 488 nm, 10 rnW/ cm2). FF for the 1TO plastic cell is 0.35. As reference a pholocurrcnl of a polycrystalline Si cell is plotted ( ), 10 limes reduced. 

I-V curves for transparent polymer solar cells illuminated from two transparent electrodes— ITO and Au. (Reused from Li, G. et al., Appl. Phys. Lett, 88,253503, 2006. With permission.)... 

Selenium exhibits both photovoltaic action, where light is converted directly into electricity, and photoconductive action, where the electrical resistance decreases with increased illumination. These properties make selenium useful in the production of photocells and exposure meters for photographic use, as well as solar cells. Selenium is also able to convert a.c. electricity to d.c., and is extensively used in rectifiers. Below its melting point selenium is a p-type semiconductor and is finding many uses in electronic and solid-state applications. 

Global AMI.5 sun illumination of intensity 100 mW/cm ). The DOS (or defect) is found to be low with a dangling bond (DB) density, as measured by electron spin resonance (esr) of - 10 cm . The inherent disorder possessed by these materials manifests itself as band tails which emanate from the conduction and valence bands and are characterized by exponential tails with an energy of 25 and 45 meV, respectively the broader tail from the valence band provides for dispersive transport (shallow defect controlled) for holes with alow drift mobiUty of 10 cm /(s-V), whereas electrons exhibit nondispersive transport behavior with a higher mobiUty of - 1 cm /(s-V). Hence the material exhibits poor minority (hole) carrier transport with a diffusion length <0.5 //m, which puts a design limitation on electronic devices such as solar cells. 

ZnO instead of T1O2 because ZnO provides a 220 times higher mobility for photoinjected electrons, which would allow reduction of the exciting laser intensity. The slow PMC decay of TiOrbased nanostructured sensitization solar cells (the Ru complex as sensitizer), which cannot be matched by a single exponential curve and is influenced by a bias illumination, is strongly affected by the concentration of iodide in the electrolyte (Fig. 38). On the basis of PMC transients and their dependence on the iodide concentration, a kinetic mechanism for the reaction of photoinjected electrons could be elaborated.40... 

Fig. 5.2 The n-Cd(Se,Te)/aqueous Cs2Sx/SnS solar cell. P, S, and L indicate the direction of electron flow through the photoelectrode, tin electrode, and external load, respectively (a) in an illuminated cell and (b) in the dark. For electrolytes, m represents molal. Electron transfer is driven both through an external load and also into electrochemical storage by reduction of SnS to metaUic tin. In the dark, the potential drop below that of tin sulfide reduction induces spontaneous oxidation of tin and electron flow through the external load. Independent of illumination conditions, electrons are driven through the load in the same direction, ensuring continuous power output. (Reproduced with permission from Macmillan Publishers Ltd [Nature] [60], Copyright 2009)...

FIG. 62. Normalized solar cell efficiency as a function of illumination time for different power densities as obtained by continuous illumination of 1000-W/m" AM 1.5 light. The initial efficiencies of the four cells were 9%, 109f. 9c. and 69c for 28-. 42-. 57-. and 113-mW/cm power density, respectively. 

Illumination of solar cells causes a reduction of efficiency and fill factor, as a result of light-induced creation of defects (Staebler-Wronski effect. Section 1.1.2.5). This reduction is halted after several hundred hours of illumination. The reduction is correlated with solar cell thickness. A large intrinsic layer thickness leads to a large reduction of efficiency and fill factor compared to a small intrinsic layer thickness. The solar cell properties can be completely recovered by annealing at about 150°C. The open circuit voltage and short circuit current decrease only slightly. 

Chu, D., Wang, S., Zheng, P., Wang, J., Zha, L Hou, Y He, J., Xiao, Y Lin, H and Tian, Z. (2009) Anode catalysts for direct ethanol fuel cells utilizing directly solar light illumination. ChemSusChem,... 

Fig. 6. I(V) characteristic at AMI illumination of solar cell consisting of p-n junction in polycrystalline Si. [Courtesy of B.W Faughnan]... 

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