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740 MEASUREMENT AND CHARACTERIZATION<br />

Shutter<br />

Filter wheel(s)<br />

W or Xe<br />

source<br />

Lens<br />

Mirror<br />

Chopper<br />

Shutter & stepper motor or<br />

solenoid control lines<br />

PV<br />

Reference<br />

detector<br />

Sync. from<br />

chopper<br />

Vacuum stage (5–100°C)<br />

Computer<br />

Lock-in<br />

amp.<br />

I to V<br />

converter<br />

GPIB interface<br />

Figure 16.9<br />

system<br />

Typical narrow-band interference filter-based spectral responsivity measurement<br />

Bias light<br />

Monochromatic light<br />

from filter system<br />

Bias light<br />

Aperture to illuminate 1 cell<br />

Series-connected<br />

thin-film module<br />

Negative<br />

Mask to block bias light to<br />

cell being measured<br />

Positive<br />

Figure 16.10<br />

Apparatus for measuring the spectral responsivity of a single cell in a multicell module<br />

The solution to the problem of measuring S(λ) of a single cell in a module is the<br />

following sequence of steps [147]:<br />

1. Bias the module with light to simulate “1 sun.”<br />

2. Forward-bias the module to the measured module open-circuit voltage (V OC ) under the<br />

bias light in the previous step multiplied by (n − 1)/n, wheren is the number of cells<br />

in series. Another procedure is to apply monochromatic light at a wavelength that the

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