Temperature Coefficient Of Current Research Articles

Temperature Coefficients of Perovskite/Silicon Tandem Solar Cells

Contrasting with single-junction photovoltaic technologies, the short-circuit current temperature coefficient of perovskite/silicon tandem solar cells can be negative, positive, or a mix of both depending on the solar spectrum and operating temperature range.

Uncertainty analysis of photovoltaic cells to determine probability of functional failure

In engineering practice, extensive uncertainties exist in photovoltaic (PV) cell material parameters owing to manufacturing process errors and in PV cell working environment parameters owing to environmental uncertainties. Ignoring the uncertainty of these parameters will greatly reduce the reliability of photovoltaic cells. In this study, a PV cell model was used to conduct an uncertainty analysis based on functional failure. Functional failure is defined as output power fluctuation beyond the specified range, and functional safety region is defined as the allowable fluctuation range of output power during operation. A global sensitivity analysis method based on the Monte Carlo method was employed to study the influence of parameter fluctuation on the functional failure probability of a PV cell. An uncertainty analysis method based on Latin hypercube sampling was applied to study the influence of parameters on the probability of PV cell operation in the functional safety domain. The results indicate that the uncertainty of surface temperature had the most significant influence on the failure probability, followed by the ideality factor, radiation intensity, and current temperature coefficient, the series and parallel resistances had the smallest impact. Optimal values of 510.200 W/m2, 284.600 K, and 1.446 were obtained for radiation intensity, surface temperature, and ideality factor, respectively, which ensured that system functional failure probability remained in the safety zone with values of 93.763 %, 99.211 %, and 98.856 %, respectively. Additionally, the lower series resistance and the higher parallel resistance, the more likely the system to operate in the functional safety domain. The results of study expand the evaluation standard for PV cell operation and ensure the desired system output power.

The analysis of parameter uncertainty on performance and reliability of photovoltaic cells

In engineering practice, the parameters affecting the output of a photovoltaic cell such as its irradiation intensity, surface temperature, current temperature coefficient, series resistance, parallel resistance, and ideality factor each inevitably possess a degree of uncertainty. Based on a photovoltaic cell model, this study uses the quasi-Monte Carlo method to model the randomness of these parameters, then discusses the influence of the uncertainty of each parameter on the output power performance, stability, and reliability. The results show that a high current temperature coefficient is beneficial to the average output power and fill factor. The smaller the series resistance and the greater the parallel resistance, the greater the mean and standard deviation of the output power and fill factor. In a normal working environment, the lower the average surface temperature, the higher the mean output power and fill factor, and the smaller the standard deviation of the output power. Finally, optimal values of the ideality factor and radiation intensity are found to exist for the mean output power. The research in this paper expands the performance evaluation standards of photovoltaic cells and provides a theoretical and technical basis for the optimization of photovoltaic cell designs that accounts for parameter randomness. • The influence of the randomness of parameters on the output performance is studied. • The influence of each variable on the performance of PV cell model is quantified. • The results can be used to extend the criteria used to evaluate PV cell. • The results can provide a theoretical basis for the optimization of PV cell.

Thermometric SOI lateral diodes for bolometric application: Comparison between Schottky and p-i-n diodes

The thermometric behavior of lateral 50-nm thin Silicon-On-Insulator (SOI) diodes are studied down to 80 K, close to liquid-nitrogen temperature. A comparison between PtSi/n-Si Schottky and implanted p-i-n diodes is presented. In this study, the intrinsic region is a moderately-doped n-type region. Key figures are extracted at room and cryogenic temperatures for each diode. A Temperature Coefficient of Current (TCC) of 6 %/K at 298 K and for a bias current of 10 pA/µm is measured for both the Schottky Barrier Diode (SBD) and the p-i-n diode. Based on simulation results, both diode types should demonstrate an increase of the TCC in the cryogenic regime. However, experimentally, only the p-i-n configuration exhibits an increase with a TCC at 81.5 K reaching more than 15 %/K at low forward bias. Some arguments are presented to account for the discrepancy between simulation and experiment, especially in the case of the SBD. Suitability as thermometer for bolometric detection is discussed.

Results of four European round-robins on short-circuit current temperature coefficient measurements of photovoltaic devices of different size

Within the EURAMET ENG55 “PhotoClass” project, several characteristics of photovoltaic (PV) devices beyond their performance at Standard Test Conditions were investigated, including measurements at varying irradiance and temperature. Four groups of PV devices of different size and technology were prepared and corresponding round-robins were run between partner laboratories with substantially different facilities and methods – namely based on spectral or integral measurements. This paper presents the outcome of the four inter-laboratory comparisons dealing with temperature coefficient measurements of the short-circuit current of PV devices, from reference-cell size to full-size commercial modules of mainly several c-Si technologies, but also with some examples of CIGS and GaAs devices. The measurement results are compared via En number assessment, hence including measurement uncertainties. The main outcome of this measurement exercise is a very good agreement of all the laboratories although completely different approaches were applied. In some cases, laboratory measurement uncertainties are even considered rather conservative and could therefore be revised. Furthermore, a comparison between bare cells and commercial modules of the same technology is made, which may represent useful information for PV manufacturers.

Effective Irradiance Ratios to Improve I–V Curve Measurements and Diode Modeling Over a Range of Temperature and Spectral and Total Irradiance

We present an integrated measurement and modeling approach based on the effective irradiance ratio, which is simply the ratio of the short-circuit current of a photovoltaic (PV) device under operating conditions to its short-circuit current under standard test conditions. Using a PV reference device to measure effective irradiance with respect to a standard spectrum, this approach handles device-specific and reference-device-specific temperature and spectral irradiance effects that are significant factors in performance measurements, such as IEC 61853-1, as well as in the diode-based equivalent circuit performance models that are calibrated from such measurements. Avoiding the use of spectrally dependent short-circuit current temperature coefficients, this approach uses a temperature-dependent spectral correction function that is a direct extension of the standardized spectral correction parameter used by numerous PV calibration laboratories. When a matched reference device is used, this function becomes identically one, and it need not be computed. This approach should be useful in the advancement of PV performance testing and modeling that use reference devices to monitor irradiance.

Temperature Dependence on the Photovoltaic Properties of Selected Thin-Film Modules

An important requirement in the employment of the different existing PV technologies is the understanding of the performance exhibited by each technology, once installed outdoors. Such records are necessary since the outdoor PV electrical characteristics are different from those corresponding to STC (which rarely occurs outdoors) information listed in manufacturer data-sheets. Therefore the PV monitoring and evaluations, under different environmental conditions, are indispensable for the architects and PV systems installers, in order to accurately size the installations. In this paper the influence of temperature on the photovoltaic parameters of amorphous silicon (a-Si) and copper indium diselenide (CIS) thin film modules has been investigated, as well as the energy produced under actual operating conditions. The cur-rent-voltage characteristics and maximum power have been recorded at regular intervals, for one year in the Mediterranean climate city of Patras, Greece (latitude 380). Patras averages over 4.2 peak sun hours (PSH) per day and module working temperatures between 16 0C and 600C. Our results have shown that, the percentage reduction of the open circuit voltage with temperature increase is greater for the CIS than for the a-Si modules. The short circuit current temperature coefficient for the CIS modules is positive at low and medium temperatures, though over the entire range of working temperature remains approximately constant with a slight tendency to reduce. The maximum power decreases almost linearly, while the efficiency for temperatures higher than 50oC reduces sharply. It is remarkable that with respect to the temperature increase the a-Si modules efficiency remains very near to the rated value, and the short circuit current temperature coefficient and the power coefficient are positive. The fill factor for these modules decreases linearly and equally as a function of temperature. The series and parallel resistance for the a-Si decrease slightly with temperature increase, whereas for the CIS the series resistance increases and the parallel resistance decreases in a more pronounced way. Maximum year-round energy production corresponds to the tilt angles of about 20 and 50 degrees in the summer and winter respectively.

Obtaining small photovoltaic array operational curves for arbitrary cell temperatures and solar irradiation densities from standard conditions data

ABSTRACTThe paper presents a simple approach to deriving I–V curves of photovoltaic panels and small arrays for arbitrary environmental conditions on the basis of three points of a single operating curve data and short current temperature coefficient only. The proposed method does not employ fitting of any type and is solely based on a numerical solution of a system of transcendental equations. The equations are expressed in a dimensionless form, simplifying both the solution and photovoltaic panel parameters' representation. The solution is used to find the values of normalized equivalent circuit elements for the available data and then perform an appropriate adjustment to obtain the operating curves for arbitrary conditions. The proposed method was applied to monocrystalline and polycrystalline commercial solar panels and was compared with both manufacturer‐provided and experimentally measured operating curves to analyze the approach applicability and accuracy. Copyright © 2012 John Wiley & Sons, Ltd.

Investigations on the temperature dependence of CPV modules equipped with triple‐junction solar cells

AbstractThis paper deals with the temperature impact on the IV curve of concentrator photovoltaic (CPV) modules equipped with III–V triple‐junction solar cells. The electrical parameters of three FLATCON® type CPV modules are investigated using a sun simulator, where the module temperatures are varied by heating with infrared (IR) bulbs. It is found that all electrical parameters vary linearly to a change of temperature. The open circuit voltages and the fill factors (FFs) of the CPV modules decrease with increasing temperature. The relative decrease in open circuit voltage of the CPV modules is similar to the value of individual triple‐junction solar cells. In contrast, the short circuit current temperature coefficients are found to be different. The experimental results can be explained by considering thermal expansion effects in the module and temperature dependencies of the optical efficiencies of the Fresnel lenses. Copyright © 2010 John Wiley & Sons, Ltd.

Temperature independent current biasing employing TFET

A recent study to a tunnelling field-effect transistor (TFET) reveals interesting temperature behaviour. It is found that the TFET drain current temperature coefficient varies with the applied drain and gate voltage. Explored is a circuit which exploits this unique behaviour of the TFET to achieve temperature independent current biasing.

CMOS-SOI-MEMS Transistor for Uncooled IR Imaging

This paper reports the design, fabrication technology, post-CMOS micromachining and characterization of CMOS-silicon-on-insulator (SOI)-microelectromechanical system (MEMS) transistors. The thermally isolated micromachined CMOS-SOI-MEMS transistor reported here is designed for uncooled infrared (IR) sensing and is dubbed here as ldquoTMOS.rdquo The measured dc and noise electrical characteristics of the as-processed (virgin) transistor as well as those of the post-CMOS-MEMS-processed transistor (TMOS) are reported and compared. In particular, the threshold voltage temperature dependence and the temperature coefficient of current (TCC) at subthreshold are reported. The results indicate that the post-CMOS-MEMS processing does not degrade the performance of the transistors. The electrooptical performance of the TMOS is characterized and reported. With TCC on the order of 4%-10%, depending on the gate voltage, responsivity of 40 mA/W, noise equivalent power on the order of several tens of picowatts, and calculated noise equivalent temperature difference on the order of 64 mK, this uncooled IR sensor in standard CMOS-SOI technology may provide a high performance at a lower cost compared to state-of-the-art uncooled sensors based on bolometers implemented in non-CMOS materials like vanadium oxide or amorphous silicon.

Temperature Sensitivity of SOI-CMOS Transistors for Use in Uncooled Thermal Sensing

The temperature coefficient of current (TCC) of CMOS transistors implemented on silicon-on-insulator substrates is theoretically and empirically studied for its potential use in uncooled thermal sensing. Modeling and measurements show TCC values in subthreshold of more than 6%/K, better than state of the art microbolometer temperature coefficient of resistance, and less than -0.4%/K in saturation-comparable with metals. Models and measurements are shown for the TCC dependence upon operating point, temperature and channel length. A simple semi-empirical model for the TCC at subthreshold based on long channel approximation is suggested and shown to agree with measurements for channel length down to 0.35 /spl mu/m. The model and measurements show a logarithmic tradeoff between subthreshold current and the TCC, which is important in the design of sensors.

Study of high-stability current regulators for current from 0.1A to 8A

Improving the temperature stability and widening the constant current range are two important problems to be solved in the application of the current regulators. This paper introduces a modular approach for the design of the current regulator with a very wide current range. The test results show that their output current ranges from 0.1A to 8A, with its current temperature coefficient as low as 10−4/°C to 10−5/°C and limiting voltage lower than 0.4V.

Effects of Electron Irradiation on Silicon Photovoltaic Cells

Electron irradiation of silicon photovoltaic cell causes a pronounced decrease on its output characteristics. On the other hand, short circuit current temperature coefficient is greatly increased with both; radiation fluence and energy, while open circuit voltage temperature coefficient remains fairly unaffected. Shelf annealing of the electron irradiated cell recovers about 50% of its initial output characteristics. Oven annealing was shown to have a significant effect, where heat treatment at 100°C for one hour cause the sample to regain 95% of its initial characteristics.

A comprehensive analytic model of accumulation-mode MOSFET's in PolySilicon thin films

A comprehensive analytic description of the polysilicon (poly-Si) MOSFET, operating in the accumulation mode is presented. The model is not a single crystalline analog. Rather, the formulation is based upon structural and electronic properties inherent in poly-Si thin films. The model is capable of quantitatively explaining the bulk of reported device characteristics, specifically the temperature coefficient of current (TCC). Drive and leakage current as a function of doping level are also quantitatively discussed. In addition, transconductance, drain admittance, and ON/OFF current ratio are described extensively at room temperature and above and are compared with experimental data. The role of grain boundary hydrogenation in effecting the device performance is quantified. Finally, a few pertinent design guidelines are presented.

Low-threshold high-To constricted double heterojunction AlGaAs diode lasers

Constricted double heterojunction diode lasers of relatively low CW thresholds (28-40 mA) are obtained by growing structures that maximize the amount of current flow into the lasing spot. These values are obtained while still using standard 10 microns wide oxide-defined stripe contacts. Over the 20-70 C temperature interval, threshold current temperature coefficients as high as 320 C and a virtually constant external differential quantum efficiency, are found.

Comments on "Multiple diode constant current sources"

Comment is made on the current temperature coefficient of a recently described multiple diode constant current circuit, (see S. Pookaiyaudom et al., ibid., vol.SC-12, no.5, p.587 (1977)).

Effect of emitter doping on device characteristics

The effect of emitter surface doping and emitter diffusion depth on the bandgap narrowing, temperature coefficient of collector current, temperature coefficient of current gain, and burst noise characteristics have been studied. The experimental investigation was done by fabricating two groups of n-p-n transistors. The first group of transistors was fabricated with three different emitter surface concentrations ( C_{0} = 5 \times 10^{21} , 2 × 1020, and 6 × 1019atoms/cm3) and fixed emitter depth ( X_{JE}= 1.5 µm), and the second group of transistors was fabricated with three different emitter depths (X JE = 0.8, 1.5, and 2.2 µm) and fixed emitter surface concentrations ( C_{0} = 2 \times 10^{20} atoms/cm3). The heavy doping (5 × 1021atoms/cm3) was found to have introduced a narrowing of the bandgap energy and a corresponding degradation in gain. An annealing experiment was conducted by heating the devices to 800°C for 16 h in nitrogen, and this experiment had the effect of recovering the bandgap narrowing and improving the gain. The temperature coefficient of collector current \alpha_{T}=(1/I_{c}) \cdot (\DeltaI_{c}/\DeltaT) was determined for fixed V BE and the temperature coefficient of current gain \beta_{T}=(1/\beta)(\Delta\beta/\DeltaT) was calculated for fixed I c . For the first group of transistors, α T was found to have changed from 0.04 to 0.065 (1/°C) when C 0 was changed from 6 × 1019to 5 × 1021atoms/cm3. The corresponding change in β T was from 4 × 10-4to 1 × 10-3(1/°C), indicating that the current gain for this group of transistors was much more sensitive to doping than to the collector current. For the second group of transistors, however, α T and β T were found to have changed by the same orders of magnitude as X JE was changed from 0.85 to 2.2 µm: α T changed from 0.032 to 0.062 (1/°C) and β T changed from 3 × 10-3to 6 × 10-3(1/°C). Emitter doping also showed a relationship to burst noise characteristics. Ninety-five percent of devices with low C 0 (6 × 1019atoms/cm3) were found to be free of burst noise.