Photoluminescence proofs to be quite sensitive to Dit. This is because this measurement performs without current extraction. As an example, Fig. 11 shows the simulated steady – state photoluminescence spectra as well as the transient photoluminescence decay (after an


integration of the spectra) due to a pulse-like excitation for two different values of Dit = 1.1010 cm – and Dit = 1.1012 cm – . If one integrates the spectra, the simulated measurement signals differ for more than one order of magnitude.

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Fig. 11. Screenshots of photoluminescence simulations for two different a-Si:H/ c-Si interface state densities Dit. (left) steady-state photoluminescence spectra, (right) transient photoluminescence decay after a pulse-like excitation.

Fig. 12. (left) Simulated temperature dependant photoluminescence measurements for different a-Si:H/c-Si interface state densities Dit. (right) Measured temperature dependant photoluminescence. Data from (Fuhs et. al, 2006).

The sensitivity towards D t can even be more enhanced, if one performs temperature dependant photoluminescence measurements, see Fig. 12. Here the character of the measurement even changes if Dtt is in the range 1 1010 cm – < Dit < 1 1011 cm-. For Dit < 1.1010 cm-2 the spectral emission decreases with increasing temperature, see Fig. 12, thus indicating a non noticeable amount of interface defects, whereas for example for Dit = 1.1011 cm-2 an increasing spectral emission with increasing temperature is observed (Fuhs et. al, 2006).

7. Conclusion

A mathematical description of AFORS-HET, version 2.4, a one dimensional computer program for the simulation of solar cells and solar cell characterization methods has been
stated. Some selected examples, simulating amorphous/crystalline silicon heterojunction solar cells and investigating the sensitivity of various measurement methods towards the interface state density Dit, were presented.

Updated: August 21, 2015 — 10:32 am