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Quantum Efficiency System

Photonics.com
Feb 2011
Sciencetech Inc.Request Info
 
LONDON, Ontario, Feb. 1, 2011 — Sciencetech Inc.’s SKU: SS-QE-150 quantum efficiency (QE) system comprises a 150-W tunable wavelength monochromatic light source and a separate solar simulator for use as the white light bias.

The light source is identical to the one used for the spectral response system, with a motorized optical chopper between the xenon light source and the scanning monochromator to modulate the light. A source meter used as an active load permits operating the test cell at various load conditions, including short-circuit, compensating for a series resistor required to sense the current produced by the modulated monochromatic light. This sensed current plus a reference signal at the frequency of the light modulation are both fed into the precision lock-in amplifier to allow measurement of the current generated by the modulated monochromatic light in the presence of the fixed white light bias of the solar simulator.

The geometry of the light from the monochromator is controlled to illuminate only a small rectangular section of the solar cell (typically 2 × 2 to 5 × 5 cm), assuring that 100% of the monochromatic irradiance contributes to the output signal. A calibrated detector is inserted at a focal point in the monochromatic light path where it can capture the total amount of monochromatic light that will fall onto the solar cell during the test, and a calibration scan is taken, usually before each run, to allow absolute external QE to be calculated.

The SS-QE system includes a SCIRUNQE I-V-Test measurement system and software that controls the monochromator, source meter and lock-in amplifier to automatically measure the I-V characteristics and QE vs. wavelength, plotting the results onscreen and outputting calculated results plus the raw measurements to a standard file format.

The spectral response and QE measurement systems provide an overall external QE value that doesn’t consider that some of the light is reflected or transmitted by the solar cell. To measure the QE of the cell material itself apart from these losses – the internal QE – the reflected and transmitted light must be measured and mathematically deducted so that only the light absorbed by the solar cell is considered in the calculations.

Lower- and higher-power versions are available upon request.


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GLOSSARY
internal
With reference to absorbance, absorptance, transmittance and the like, the processes occurring within a specimen between the entry and exit surfaces.
lock-in amplifier
A form of synchronous detector having a balanced amplifier in which the signal is applied to the grids of two tubes as the control signal is applied to their plates or another grid. The difference in output currents is then measured.
monochromatic
Composed of one color; having only one wavelength of radiation.
optical chopper
A mechanical or electrical-electromagnetic device for periodically interrupting or blocking abeam of light for a brief known interval. The three most common chopper types include the tuning fork chopper, the rotating shutter chopper (also referred to as rotating disc chopper) chopper and the more sophisticated optical chopper such as the Kerr cell.
solar cell
A device for converting sunlight into electrical energy, consisting of a sandwich of P-type and N-type semiconducting wafers. A photon with sufficient energy striking the cell can dislodge an electron from an atom near the interface of the two crystal types. Electrons released in this way, collected at an electrode, can constitute an electrical current.
xenon
A rare gas used in small high-pressure arc lamps to produce a high-intensity source of light closely resembling the color quality of daylight.
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