Solar cells conversion efficiency

Wang C, Bahnemann DW, Dohrmann JK (2000) A novel preparation of iron-doped Ti02 nanoparticles with enhanced photocatalytic activity. Chem Commun 16 1539-1540 Wang Y, Hao Y, Cheng H, Ma H, Xu B, Li W, Cai S (1999) The photoelectrochemistiy of transition metal-ion-doped Ti02 nanociystalline electrodes and higher solar cell conversion efficiency based on Zn -doped Ti02 electrode. J Mater Sci 34 2773-2779... 

Another species might contribute to the chemistry and electronic properties at the interface. As evident from the In MNN spectra shown in Fig. 4.28, there is also sodium present at the surface. The sodium diffuses from the soda lime glass substrate during deposition of the Cu(In,Ga)Se2 film and has a beneficial effect on the solar cell conversion efficiency [139]. As mentioned... 

MSP titania was also used to make electrodes, which were tested in a dye-sensitized solar cell [116]. The short-circuit photocurrent, open-circuit photovoltage and fill factor increased with increasing sintering temperature, having a performance threshold at 450 °C, showing that the more ordered structures are required for high solar cell conversion efficiencies. 

When the temperature of a solar cell rises, cell conversion efficiency decreases because the additional thermal energy increases the thermally generated minority (dark-drift) current. This increase in dark-drift current is balanced in the cell by lowering the built-in barrier potential, lU, to boost the majority diffusion current. The drop in F causes a decrease in and F. Therefore, a cell s output, ie, the product of F and decreases with increasing cell temperature. is less sensitive to temperature changes than F and actually increases with temperature. 

Designing tandem cells is complex. For example, each cell must transmit efficiently the insufficiently energetic photons so that the contacts on the backs of the upper cells are transparent to these photons and therefore caimot be made of the usual bulk metal layers. Unless the cells in a stack can be fabricated monolithically, ie, together on the same substrate, different external load circuits must be provided for each cell. The thicknesses and band gaps of individual cells in the stack must be adjusted so that the photocurrents in all cells are equal. Such an optimal adjustment is especially difficult because the power in different parts of the solar spectmm varies under ambient conditions. Despite these difficulties, there is potential for improvement in cell conversion efficiency from tandem cells. 

Mullen et al. in 2008 reported the successful use of graphene films (TGF) as transparent electrodes (anodes) in BHJ solar cells composed of P3HT and PCBM as the active layer (see Fig. 34) [258]. The cell conversion efficiency under low intensity monochromatic light showed the same values as the ITO electrode (1.5%) and under simulated solar light the values were lower (0.29%) compared to the obtained values for ITO (1.17%) under the same conditions. Although the study under simulated solar light was not satisfactory, the BHJ solar cell shows promise for the use of graphene in this type of devices after further optimization of the cell. 

High solar-energy conversion efficiency. A high efficiency equal to that of the amorphous Si solar cell has been obtained as a laboratory development and efficiencies greater than 10% might be possible. 

Finally, for the hydrogen fuel cell car, the solar radiation to wind conversion-efficiency is taken as 100% (following arguments of Sorensen, 1996c), the wind turbine efficiency as 35%, the electrolysis efficiency as 80%, the fuel cell conversion efficiency as 55% and the rest as for methanol. The overall accumulated efficiencies are 1.4 x 10 for the methanol route and 0.054 for the wind-hydrogen route. 

There are two fundamental approaches for enhancing the solar photon conversion efficiency increased photovoltage (Boudreaux et al, 1980 Ross and Nozik, 1982) and increased photocurrent (Kolodinski et al, 1993 Landsberg et al, 1993). These can be accessed, in principle, in at least three different QD solar cell configurations these configurations are shown in Fig. 3.19 and described below. 

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