Spectral Response Measurement System Research Articles

Improving Spectral Responsivity Measurements by Correcting for Filter Bandwidth

Spectral responsivity (SR) measurements are key in characterizing photovoltaic (PV) devices and calculating spectral mismatch correction factors (MMF). SR is measured using different wavelengths of monochromatic light. In practical measurement systems, this light has a finite bandwidth, meaning that it is only quasi-monochromatic. The data analysis, however, typically assumes perfectly monochromatic light. The accuracy of the calculated SR then depends not only on the actual bandwidth of the monochromatic light used during the measurement but also on the intensity distribution inside the bandwidth. In our SR measurement system, we use quasi-monochromatic light obtained from a solar simulator and a range of bandpass filters. First, we measured and analyzed the spectral content of light transmitted for each filter. Then, we developed an iterative correction scheme for the measured SR. This numerical approach assumes no previous knowledge about the SR of the device under test (DUT). Applying this scheme for bandwidth correction to a range of PV cells with varying SR curves, we found that the corrections for most wavelengths are of minor importance. However, for those wavelengths where the shape of the SR curve of the reference device and DUT differ notably, the corrections are significant up to 20% and higher. We investigated the change in the spectral MMF, which was found to be negligible in most cases but not always. Therefore, the bandwidth correction is mainly important not only for improving SR measurements of PV devices but also relevant for the determination of spectral mismatch factors.

Development of a Compact, Cost-Effective Photoacoustic Spectral Response Measurement System for Biomedical Applications

Photoacoustic spectral response (PASR) technique is a pump-probe technique that provides acoustic spectral information of any biological tissue. This extracted information acts as a signature of the biological tissue. The experimental setups can be bulky, expensive, and involve complex operation due to the requirement of costly Q-switched lasers, complex optics, and limited wavelength. On the other side, setup requires high-frequency signal conditioning, a high-speed oscilloscope, and a computing device to process, analyze, and monitor the acquired signal. This paper presents a compact, cost-effective measurement instrument to measure and display the time-domain and frequency spectral information for biomedical applications. The developed electronic hardware is used to perform real-time signal conditioning; subsequently, conditioned photoacoustic (PA) data were acquired with a speed of 30 MSPS, and the results were sent to a monitor to display. Developed hardware contains a high-frequency pre-amplifier, low-pass filter, electrically isolated trigger circuit, and a 12-bit high-speed analog-to-digital converter to generate digital data, which is further analyzed by a high-speed microcontroller. After calibration of the proposed experimental setup, the developed PA tool is applied to distinguishing lung and liver tissues, and the statistical results corroborate the consistency of the proposed PA-based data acquisition system.

Band gap Measurement of P – type Monocrystalline Silicon Wafer

Band gap of P-type monocrystalline silicon wafer has been measured using spectral response measurement system. To see the spectral response a SR510 lock in amplifier, SR540 optical chopper, monochromator (400nm-1200nm), optical detector and lab view software has been used. From spectral response of polished P-type monocrystalline silicon wafer absorption, reflection and transmission has been respectively seen from 400nm-550nm, 550nm-1050nm and 1050-1200nm. Assuming band gap of silicon is (1.12eV), this result has been theoretically verified using Planck–Einstein relation. Moreover, theoretical band gap of silicon has been calculated (1.127362 eV). The band gap measurement process uses partial concept of Tauc’s downhill negative slop and Planck–Einstein relation. Experimental result shows that, the band gap of silicon is 1.127907 eV.Bangladesh J. Sci. Ind. Res.53(3), 179-184, 2018

A differential spectral responsivity measurement system constructed for determining of the spectral responsivity of a single- and triple-junction photovoltaic cells

A differential spectral responsivity (DSR) measurement system has been designed and constructed at National Metrology Institute of Turkey (TUBITAK UME) to determine the spectral responsivity (SR) of a single- or a multi-junction photovoltaic device (solar cell). The DSR setup contains a broad band light bias source composed of a constructed Solar Simulator based on a 1000 W Xe-arc lamp owning a AM-1.5 filter and 250 W quartz-tungsten-halogen lamp, a designed and constructed LED-based Bias Light Sources, a DC voltage bias circuit, and a probe beam optical power tracking and correction circuit controlled with an ADuC847 microcontroller card together with an embedded C based software, designed and constructed in TUBITAK UME under this project. By using the constructed DSR measurement system, the SR calibration of solar cells, the monolitic triple-junction solar cell GaInP/GaInAs/Ge and its corresponding component cells have been performed within the EURAMET Joint Research Project SolCell.

Spectral response characteristics of transmission-mode alkali telluride photocathodes working from vacuum-ultraviolet to ultraviolet band

In order to characterize the spectral response of transmission-mode alkali telluride photocathodes, a spectral response measurement system for image intensifiers working from the vacuum-ultraviolet to ultraviolet band is developed. Using this system, the transmittance curves of usual window materials such as quartz, MgF2, and sapphire selected to prepare alkali telluride photocathodes are measured. In addition to the transmittance test function, the spectral response of image intensifiers based on transmission-mode alkali telluride photocathodes, such as Cs2Te, Rb2Te, Cs-K-Te, and Rb-K-Te photocathodes, under the excitation light from 115 to 400 nm is measured. The measured results show that the longwave cutoff wavelength of the Rb2Te photocathode is 313 nm, while that of the Cs2Te photocathode is 342 nm, which could be ascribed to the reduced cathode work function, inversely proportional to the atomic number of the alkali element in uni-alkali telluride photocathodes. Besides, the spectral response values of Cs-K-Te and Rb-K-Te photocathodes are greater than those of Cs2Te and Rb2Te photocathodes, and this case is similar to the multialkali effect of alkali antimonide photocathodes. The cutoff wavelength can get shorter through the combination with an additional K element. Compared with the Rb-K-Te photocathode with the shorter cutoff wavelength, the Cs-K-Te photocathode can achieve higher sensitivity.

Variation of the sample temperature due to white bias light irradiation during the spectral responsivity measurement of solar cells and its effect on the measurement result

The temperature variation of solar cells due to white bias light irradiation during the spectral responsivity measurement and its effect on the spectral responsivity measurement result were investigated for various types of solar cells, such as crystalline silicon (c-Si), Cu(In,Ga)Se2 (CIGS), and dye-sensitized solar cells (DSSCs). For the investigation, a spectral responsivity measurement system, which can employ the well-known sample temperature control methods (such as the “temperature controlled sample stage” method and the “forced air cooling” method) has been used. Hence, the availability of these sample temperature control methods has also been tested. Through the investigation, it was found that the actual temperature of the solar cells located under the AM1.5G-approximated white bias light can be increased significantly during the spectral responsivity measurement, depending on the sample temperature control methods applied. In addition, it was also found that the increase of sample temperature can lead to a significant error in the measured spectral responsivity, depending on the types of solar cells being measured. In addition, a simple analytic model based on the classical heat transfer theory was developed to understand the temperature variation of the solar cells under the spectral responsivity measurement environment.

Enhancing mid-infrared spectral response at the LaAlO3/SrTiO3 interface by magnetic field

Many unexpected properties have been found in the LaAlO3/SrTiO3 heterostructure, but the interaction of the many ground states at its interface remains unclear. Here, we demonstrate an optical property of this n-type heterostructure where the mid-infrared spectral responsivity at the interface is enhanced by an external magnetic field. The field intensity ranged from 0.8 to 6 kOe at a low temperature (19 K) as measured with our spectral response measurement system. Two spectral peaks related to the spin-orbit coupling effect were also observed at wavelengths 2400 nm and 3700 nm. The intriguing phenomena relate to changes in the crystallographic structure and subband structure at the interface.

Large-area irradiance-mode spectral response measurements of solar cells by a light-emitting, diode-based integrating sphere source.

An irradiance-mode absolute differential spectral response (SR) measurement system based on a light emitting diode (LED) array is described. The LEDs are coupled to an integrating sphere whose output irradiance is uniform to better than 2% over an area of 160 mm by 160 mm. SR measurements of solar cells when subject to diffuse irradiation, as provided by the integrating sphere, are compared with collimated irradiance SR measurements. Issues originating from the differences in angular response of the reference versus the test cells are also investigated. The SR curves of large-area cells with dimensions of up to 155 mm are measured and then used to calculate the cell's short circuit current (I(sc)), if illuminated by a defined solar spectrum. The resulting values of I(sc) agree well with the values obtained from secondary measurements.

Evaluation of chemical cleaning for Ga1−xAlxAs photocathode by spectral response

The spectral response has been used to evaluate the chemical cleaning for Ga1−xAlxAs photocathode by an on-line spectral response measurement system. The spectral response curves of Ga1−xAlxAs photocathodes treated by different chemical cleaning methods are measured and analyzed in detail. We use the quantum efficiency formulas to fit the experimental curves transforming from the spectral response curves, and obtain the related performance parameters such as the surface electron escape probability, the back-interface recombination velocity, the electron diffusion length, and the thickness of the etching GaAs layer. The results show that the GaAs photocathode cleaned by the HF solution could obtain a good photoemission effect, while the Ga0.37Al0.63As photocathode could be well cleaned by the solution of sulfuric acid and hydrogen peroxide.

Absolute spectral responsivity measurements of solar cells by a hybrid optical technique

An irradiance mode, absolute differential spectral response measurement system for solar cells is presented. The system is based on combining the monochromator-based approach of determining the power mode spectral responsivity of cells with an LED-based measurement to construct a curve representing the light-overfilled absolute spectral response of the entire cell. This curve can be used to predict the short-circuit current (I(sc)) of the cell under the AM 1.5 standard reference spectrum. The measurement system is SI-traceable via detectors with primary calibrations linked to the NIST absolute cryogenic radiometer. An uncertainty analysis of the methodology places the relative uncertainty of the calculated I(sc) at better than ±0.8%.

Development of a very fast spectral response measurement system for analysis of hydrogenated amorphous silicon solar cells and modules

Abstract An important requirement for a very fast spectral response measurement system is the simultaneous illumination of the solar cell at multiple well defined wavelengths. Nowadays this can be done by means of light emitting diodes (LEDs) available for a multitude of wavelengths. For the purpose to measure the spectral response (SR) of amorphous silicon solar cells a detailed characterization of LEDs emitting in the wavelength range from 300 nm to 800 nm was performed. In the here developed equipment the LED illumination is modulated in the frequency range from 100 Hz to 200 Hz and the current generated by each LED is analyzed by a Fast Fourier Transform (FFT) to determine the current component corresponding to each wavelength. The equipment provides a signal to noise ratio of 2–4 orders of magnitude for individual wavelengths resulting in a precise measurement of the SR over the whole wavelength range. The difference of the short circuit current determined from the SR is less than 1% in comparison to a conventional system with monochromator.

Versatile light-emitting-diode-based spectral response measurement system for photovoltaic device characterization

An absolute differential spectral response measurement system for solar cells is presented. The system couples an array of light emitting diodes with an optical waveguide to provide large area illumination. Two unique yet complementary measurement methods were developed and tested with the same measurement apparatus. Good agreement was observed between the two methods based on testing of a variety of solar cells. The first method is a lock-in technique that can be performed over a broad pulse frequency range. The second method is based on synchronous multifrequency optical excitation and electrical detection. An innovative scheme for providing light bias during each measurement method is discussed.

Primary Calibration of Solar Photovoltaic Cells At the National Metrology Centre of Singapore

A multi-functional differential spectral responsivity (DSR) measurement system for primary calibration of the shortcircuit current (SCC) of reference solar cells with WPVS (World Photovoltaic Scale) design [1] is reported in this paper. Based on the dual beam principle, the system is able to measure DSR at different bias levels, spatial uniformity, linearity, temperature coefficient of the spectral responsivity of reference cells in the spectral range from 280nm to 1200nm. The measurement principle, system design and construction as well as the performance of the system are described in this work. An uncertainty ≤ 1% for SCC measurement is confirmed by experimental results.

Variation of spectral response for exponential-doped transmission-mode GaAs photocathodes in the preparation process

To confirm the actual effect of an exponential-doped structure on cathode performance, an exponential-doped structure was applied to the preparation of a transmission-mode GaAs photocathode, and spectral response curves after high-temperature activation, low-temperature activation, and the indium sealing process were separately measured by use of the on-line spectral response measurement system. The results show that, compared to the previously uniform-doped photocathode, the exponential-doped photocathode can obtain higher cathode performance and photoemission capability because of the built-in electric field. Nevertheless, cesium desorption and impurity of gas during the sealing process can cause the degeneration of spectral response in the entire response waveband, especially in the long-wavelength region, with the decrease in surface electron escape probability related to the adverse evolution of the surface potential barrier profile.

太陽紫外UV-B計測器の感度定数・分光感度評価装置の試作

太陽紫外UV-B計測器の感度定数・分光感度評価装置の試作

The effect of Be-doping structure in negative electron affinity GaAs photocathodes on integrated photosensitivity

A new structure of GaAs photocathode was introduced. The Be-doping concentration is variable in the new structure compared with the constant concentration of Be in the normal photocathode. Negative electron affinity GaAs photocathodes were fabricated by alternate input of Cs and O. The spectral response results measured by the on-line spectral response measurement system show that the integrated photosensitivity of the photocathodes with the new structure is enhanced by at least 50% as compared to those with the monolayer structure. Accordingly, two main factors leading to the enhanced photosensitivity of the photocathodes were discussed. (c) 2005 Elsevier B.V. All rights reserved.

Domestic Comparison of Relative Spectral Responsivity Measurements for Illuminance Meters.

A comparison of relative spectral responsivity measurements of illuminance meters was carried out among five companies — TOPCON Corp., HIOKI E.E. Corp., Minolta Co., Ltd., Yokogawa M&C Corp., and Matsushita Electric Industrial Co., Ltd. The spectral responsivitys of the illuminance meters were measured by each company's spectral responsivity measurement system calibrated to each company's standard. As a result, the measured values of fs (fs is defined as the relative spectral responsivity error in Japanese Industrial Standard JIS-C-1609) differed within 1.7. The fs is identical with the f1' recommended by the CIE.

A fast low-cost solar cell spectral response measurement system with accuracy indicator

A novel automated spectral measurement system is presented. Special attention has been focused on the design in order to obtain rapid measurement facilities, minimize hardware and simplify serial communications between the different subsystems involved, resulting in a low-cost measurement system. It is controlled by an HP-9000 computer, through a fully menu-driven interface, and the primary measurement instrument is an HP-4142B modular source-monitor. A new indicator of measurement accuracy is defined, implemented and displayed in real time. This automated system has been employed intensively to study characteristics of different solar cell types in order to optimize their fabrication process. As such this automated measurement system is clearly useful for both research and fabrication.

A spectral response measurement system for large-area solar cells

An optical system designed to make spectral response measurements on large-area cells is described. A high intensity “white” light beam illuminates the cell to establish a d.c. bias and a spectrally filtered beam is used to induce an a.c. photocurrent in the cell. The two beams are brought in to be collinear and combined by common optics consisting of an optical integrator and a “beam converter”. Prior to their mixing, the two beams are shaped to match each other's characteristics. The final large-area (6 in × 6 in) beams are highly uniform and illuminate the cell at near-normal incidence. Several typical applications of the system, which illustrate the need for bias light (to simulate normal operation of the cell) during spectral response measurement, are described.

Spectral response measurements on polarisation splitting ratio of fused-taper single-mode fibre couplers

Using a Ge PIN photodiode cooled to 77 K (?196°C) with liquid nitrogen and the lock-in amplification technique, an automatic polarisation spectral response measurement system with a measuring dynamic range of about 36 dB has been developed. It has been confirmed experimentally that the spectral response of polarisation beam-splitting ratios of fused-taper fibre couplers depend on the incident polarisation angle