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QE protocol:MOST

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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[edit]

A wide range of optional features are included within this system:

  • Beam-up operation
  • Beam-down operation
  • Spectral range extension to 1800 nm
  • LED bias light
  • Vacuum test fixture, 160mm X 160mm
  • Thermoelectric temperature control for vacuum test fixtures

Spectral Response[edit]

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[edit]

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.

Specifications[edit]

The QE system has the following specifications:

Wavelength Range 300 nm to 1800 nm
Wavelength Interval .5 nm to 20 nm, selectable
Monochromatic Beam Spectral Wavelength Approximately 4 nm to 5 nm FWHM, continuously adjustable to smaller or larger FWHM
Wavelength Uncertainty ±2 nm
Transfer Uncertainty ±1 % or better 400 nm to 1000 nm; ±2 % or better elsewhere for signals with QE>20 %
Repeatability Better than 0.3 % for 400 nm to 1000 nm

Better than 0.6 % for 300 nm to 400 nm and 1000 nm to 1100 nm

Chopping Frequency Range 4 Hz to 200 Hz
Bias Light Capability 0 Suns to 5 suns white (broadband)

150 mA maximum bias current 460 nm to 850 nm (LED)

Voltage Bias Capability -3.0 V to +3.0 V
Electrical Power Requirements 115 VAC, 10 A, 60 Hz
Environmental Requirements The equipment is operated in an environment with temperature between 20 °C and 27 °C, no organic vapors or corrosive fumes, and relative humidity<60 %

System Overview[edit]

The QE system has the following components:

Electronics Unit[edit]
  • Rack-mount computer with Windows 7 Professional OS
  • QE power and control unit with chopper controller
  • Rack-mount encloser
  • Custom software (LabVIEWTM executable) and license
Optics Unit[edit]
  • Optics tabletop with metric (M6)threaded holes and metric hole spacing (25 mm pitch)
  • Xenon arc lamp, housing, ellipsoidal reflector, enclosure and power supply
  • Light Chopper
  • Grating Monochromator
  • Filter wheel with harmonic rejection and stray light attenuation filters
  • Monochromator light intensity monitoring system, including beamsplitter, lens and photodiode
  • Reflective monochromatic beam focusing system
  • Signal conditioning and data acquisition unit including transimpedence amplifier
  • Bias lamp optical system including fixture, lamp, power supply, fiber optic bundle, lens, filter holder
  • Integrating sphere and photodiode for reflectance measurements
  • LED bias light system
Accessories[edit]
  • Silicon calibration photodiode
  • Germanium calibration photodiode
  • Line (narrow bandpass) filter for wavelength calibration verification
  • Spare lamps
  • Manuals for incorporated components
  • Specular reflectance standard