The Quantum Efficiency (QE)/IPCE measurement system measures the spectral responsivity of photovoltaic cell. The system uses monochromatic light source to apply specific wavelength to the device under test. It uses transimpedence amplifier to convert the induced current in the test device to a voltage, which is measured with signal conditioning equipmentand digital signal processing software. A computer controls the system components, automating data collection, analysis, reporting and calibration. The installed system is referred as the QEX10- a PV Measurements, Inc. product

System Options

A wide range of optional features are included within this system: 1. Beam-up operation 2. Beam-down operation 3. Spectral range extension to 1800 nm 4. LED bias light 5. Vacuum test fixture, 160mm X 160mm 6. Thermoelectric temperature control for vacuum test fixtures

Spectral Response

Quantum efficiency is the ratio of number of electrons delivered to an external circuit to the number of photons striking the device surface- generally expressed as a function of incident light wavelength. A solar cell's quantum efficiency graph provides a quick visual indication of the wavelengths at which there are room for improvement. The information can also be used , in conjunction with reference device quantum efficiency and test source spectrum, to compute the spectral mismatch parameter that can be applied in setting solar simulator intensity for efficiency tests. Additionally by integrating the product of the spectral response with the spectral irradiance at each wavelength the short circuit current density (Jsc) of the test devices can be estimated.

System Operation

The QE system applies monochromatic light from a xenon arc lamp as filtered by a dual-grating monochromator and individual filters to the test device. An ellipsoidal reflector collects light from the lamp and focuses it on the monochromator entrance slit via a mechanical chopper (disabled in DC mode), which modulates the light and provides a reference signal to the digital signal processor. The monochromator selects individual wavelengths of light according to commands it receives from the computer. The filter wheel inserts a wavelength appropriate filter into the beam path to attenuate stray and harmonic light. Tha monochromatic light next reaches a beamsplitter, which diverts a sample of the light to the monitor photodiode via a lens. The light passing through the beamsplliter reaches a concave mirror, which causes the beam to converge again. The test device should be mounted at or near the focal point of the beam, ensuring that the whole beam is within the test device. For system calibration a reference photodiode is mounted usually.

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