Solar cells efficiency

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. 

Using the tri-iodide/iodide redox couple and the sensitizers (22) and (56), several groups have reported up to 8-10% solar cell efficiency where the potential mismatch between the sensitizer and the redox couple is around 0.5 V vs. SCE. If one develops a suitable redox couple that decreases the potential difference between the sensitizer and the redox couple, then the cell efficiency could increase by 30%, i.e., from the present value of 10% up to 13%. Towards this goal, Oskam et al. have employed pseudohalogens in place of the triiodide/iodide redox couples, where the equilibrium potential is 0.43 V more positive than that of the iodide/iodide redox couple.17 Yamada and co-workers have used cobalt tris-phenanthroline complexes as electron relays (based on the CoII/m couple) in dye-sensitized solar cells.95... 

P.T. Landsberg, H. Nussbaumer, G. Willeke, Band-band impact ionization and solar cell efficiency, J. Appl. Phys. 7A (1993) 1451-1452. 

Green MA, Emery K, Hishikawa Y, Warta W (2010) Solar cell efficiency tables (version 36). Prog Photovoltaics 18 346... 

Emery KA, Osterwald CR (1986) Solar-cell efficiency measurements. Sol Cells 17 253 Matson RJ, Emery KA, Bird RE (1984) Terrestrial solar spectra, solar simulation and solarcell short-circuit current calibration - a review. Sol Cells 11 105... 

Figure 2. Ideal p-n junction solar cell efficiencies plotted against band gap energy [3]...

Green, M. et al., Solar Cell Efficiency Tables, Key Center for Photovoltaics, University of New South Wales (2001) http //www.pv.unsw.edu.au/eff/. 

In addition to the existing technologies, research is continuing on designs for new and more efficient converters. For example, researchers at Penn State University are working on new ways to harness the power of the sun by using highly ordered arrays of titania nanotubes for H2 production and increased solar cell efficiency. 

Another interesting work is the recent report by Licht et al [72, 75, 94]. Although the system they studied was not a strict photoelectrochemical one, since the photovoltaic system was separated from the water electrolyser, their study is of general interest for the water oxidation field. The photovoltaic cell was connected to a water splitter catalyst system of considerably larger area than the solar cell. With this design, it was possible to combine a high solar cell efficiently with a low photocurrent density over the electrolyzer (jph = 0.44 mA/cm2), which minimized the overpotential needed for water oxidation. An overall efficiency as high as 18.3% was obtained. 

Solar-Cell Efficiencies for Various Growth Techniques... 

Optical measurements showed that a small concentration of 2% is effective in quenching the PL of MDMO but a high concentration of more than 67% is required to increase the photoconductivity or the short circuit current of a BHJSC. The solar cells efficiency measurements show that the optimum PCBM concentration is 80%. See next section. 

Improvements in solar cell efficiency, by system, 1976-2004. From Surek [4],... 

Table 1. Benchmark (10-MW) System parameters and impact of multijunction (III-V) solar cell efficiency on a CPV utility reference system.7 High-efficiency solar cells are installed in essentially identical solar concentrator structures, and the cost per watt drops from about 6/watt to well under 2/watt while electricity costs fall below 10 cents per kWh. Higher production levels can lead to even lower levelized costs of energy (LCOE).7...

These early tests were not conducted with the most efficient solar cells available at that time. The record efficiency then was about 30% for a laboratory cell (see Fig. 4) and those cells were not easily obtainable. Today s record efficiency is 40.7%, and 35% efficient cells are commercially available.18 Therefore, 40% solar to hydrogen efficiency is expected in the near term assuming a heat boost of 40%, a multijunction solar cell efficiency of 35%, and an optical efficiency of 85%. A 40% multijunction solar cell would yield a solar to hydrogen conversion efficiency of almost 50%. Nevertheless, electrochemical theoretical results calculated by Licht, shown in Figure 10, are consistent with these predictions based on Solar Systems early experiments.15... 

The hybrid solar concentrator is a potential leap frog technology that may rapidly lower the cost of clean hydrogen in light of the following the imminent market entry of CPV systems for electricity production solar cell efficiencies above 40%, with clearer ideas for 50%-efficient solar cells and the opportunity to use wasted solar heat for augmenting solar electrolysis. 

The growth of quadratic FZ crystals could reduce the material waste for solar cell production. High carrier diffusion length and low oxygen concentration enable the highest solar cell efficiencies of about 25% in laboratory scale. 

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