Silicon cell quantum efficiency

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. 

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. 

Fig. 8.5. Quantum efficiency of an amorphous/microcrystalline silicon tandem junction solar cell. The individual quantum efficiency curves of the two component cells (a-Si H top (dotted) and pc-Si H bottom (dashed,)) are also included...

Fig. 8.10. Measured (dashed lines) and calculated (solid) quantum efficiency (QE) and total cell absorption (1 — R) according to Springer et al. [58]. The area between QE and (1 — R) corresponds to the absorption losses in 330 nm thick front ZnO Al (single diagonally hatched), doped silicon (p layer double diagonally hatched, n layer white), silver (black), and glass + back ZnO (horizontally hatched). The area above the silver absorption (black) and the total cell absorption (dashed) corresponds to cell reflection R. Reprinted with permission from [58]...

Fig. 9. Quantum efficiency as a function of wavelength for a p-i-rt cell with t] — 10.1% [From Catalano et al., Attainment of 10% conversion efficiency in amorphous silicon solar cells. Conf. Rec. IEEE Photovoltaic Spec. Conf., Vol. 16, 1982 IEEE.]...

Obviously, the performance of organic cells having bicontinuous network structures with quantum efficiencies of about 50% and power conversion efficiencies of about 5% remains far inferior to that of silicon cells, but is highly improved as compared to that of flat-junction organic cells, which have both quantum efficiencies and power conversion efficiencies of less than 0.1%. 

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