4

i / .*•'/1 i i I

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Photon energy, eV

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Photon energy, eV

Figure 8 The effects observed near the absorption edge at high doping concentrations, illustrated here on the example of n-type silicon (from reference [ 30], as adapted by M.A. Green. Silicon Solar Cells - See Bibliography).

The following sections give a brief summary of the main recombination mechanisms with relevance to solar cell operation which are summarised schematically in Figure 9.

7.1 Bulk Recombination Processes

A detailed discussion of the variety of the bulk recombination mechanisms can be found in [32]. Here, we confine ourselves to a brief overview of the radiative, Auger and defect-assisted recombination processes which are most frequently encountered in practical operation of solar cells. These processes are depicted schematically in Figure 9 which also shows the notation used to describe the relevant parameters.

The rate of band-to-band radiative recombination can be written in the form

where the coefficient B is sometimes written as R/n{2. Radiative transitions between a free electron and a localised state within the band gap may also be important in certain situations, for example in novel concepts such as the

Table 11 The coefficients B of the radiative recombination rate (Equation (20)) and C„0 and Cp0 of the Auger recombination rate (Equation (21)). Sources of data: (a) [34]; (b) [32]; (c) [35]; (d) [26]
0 0

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