Extremely thin absorber ETA cells

At their present state of development, ETA cells typically exhibit open-circuit voltages of 0.6-0.7 V and photocurrents of 5-15 mA cm . While the fill factors in the earlier ETA cells were often poor, typically -20%, more recent cells have improved fill factors, typically -60%. Overall, the solar conversion efficiencies are modest, as shown in Fig. 1.2 to date ri p values of approximately 5% have been obtained (Nanu et al., 2005). Insertion of an ultrathin mnnel barrier layer of an insulator such as AI2O3 or MgO can improve the open-circuit voltage (Wienke et al., 2003). Incorporation of quantum 

The technology of ETA cells is not yet mature, and future improvements in their efficiency can reasonably be expected. Modelling calculations (Taretto and Rau, 2005) indicate that 15% efficient CdTe ETA cells are possible even at electron diffusion lengths as low as 10 nm, provided that the built-in voltage is optimised to restrict recombination over the working bias range of the cell. If efficiency improvements of this order can be achieved and fabrication methods can be satisfactorily scaled up, ETA cells could offer a low-cost, stable alternative to traditional photovoltaic cells and dye-sensitised solar cells. 

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