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Sandip K Chakrabarti - One of the best experts on this subject based on the ideXlab platform.
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effective Recombination Coefficient and solar zenith angle effects on low latitude d region ionosphere evaluated from vlf signal amplitude and its time delay during x ray solar flares
arXiv: Space Physics, 2013Co-Authors: Tamal Basak, Sandip K ChakrabartiAbstract:Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron Recombination Coefficient ($\alpha_{eff}$) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay ($\bigtriangleup t$). For the C-class flares we find that there is a direct correspondence between $\bigtriangleup t$ of a solar flare and the average solar zenith angle $Z$ over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the $\bigtriangleup t$ for different local diurnal time slots $DT$. We find that while the time delay is anti-correlated with the flare peak energy flux $\phi_{max}$ independent of these time slots, the goodness of fit, as measured by $reduced$-$\chi^2$, actually worsens as the day progresses. The variation of the $Z$ dependence of $reduced$-$\chi^2$ seems to follow the variation of standard deviation of $Z$ along the $T_x$-$R_x$ propagation path. In other words, for the flares having almost constant $Z$ over the path a tighter anti-correlation between $\bigtriangleup t$ and $\phi_{max}$ was observed.
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effective Recombination Coefficient and solar zenith angle effects on low latitude d region ionosphere evaluated from vlf signal amplitude and its time delay during x ray solar flares
Astrophysics and Space Science, 2013Co-Authors: Tamal Basak, Sandip K ChakrabartiAbstract:Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. VLF signal amplitude perturbation (ΔA) and amplitude time delay (Δt) (vis-a-vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz signal have been computed for solar flares which is detected by us during Jan–Sep 2011. The signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22∘ 27′N, 87∘ 45′E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron Recombination Coefficient (αeff) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (Δt). For the C-class flares we find that there is a direct correspondence between Δt of a solar flare and the average solar zenith angle Z over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the Δt for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux ϕmax independent of these time slots, the goodness of fit, as measured by reduced-χ2, actually worsens as the day progresses. The variation of the Z dependence of reduced-χ2 seems to follow the variation of standard deviation of Z along the Tx-Rx propagation path. In other words, for the flares having almost constant Z over the path a tighter anti-correlation between Δt and ϕmax was observed.
Jean-paul Kleider - One of the best experts on this subject based on the ideXlab platform.
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radiative Recombination Coefficient in crystalline silicon at low temperatures 77 k by combined photoluminescence measurements
Energy Procedia, 2017Co-Authors: Rudolf Brüggemann, José Alvarez, Mohamed Boutchich, Jean-paul KleiderAbstract:Abstract Spectral photoluminescence (sPL) and modulated photoluminescence (MPL) measurements were applied to determine the band-to-band radiative Recombination Coefficient, Brad, in crystalline silicon. We used precursors of n-type crystalline silicon solar cells consisting of two different wafers passivated with aluminum oxide stacks or intrinsic hydrogenated amorphous silicon, respectively. So far values for Brad can be found in the literature only above 77 K. In this high-temperature range the temperature dependence of Brad obtained using our combined sPL/MPL method is in good agreement with the available literature data for both samples. Interestingly, we have extended the measured range down to a temperature of 20 K and observed a strong increase of Brad by three orders of magnitude with decreasing temperature from 77 K to 20 K.
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Radiative Recombination Coefficient in crystalline silicon at low temperatures < 77 K by combined photoluminescence measurements
Energy Procedia, 2017Co-Authors: Rudolf Brüggemann, José Alvarez, Mohamed Boutchich, Jean-paul KleiderAbstract:District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope Coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract Spectral photoluminescence (sPL) and modulated photoluminescence (MPL) measurements were applied to determine the band-to-band radiative Recombination Coefficient, B rad , in crystalline silicon. We used precursors of n-type crystalline silicon solar cells consisting of two different wafers passivated with aluminum oxide stacks or intrinsic hydrogenated amorphous silicon, respectively. So far values for B rad can be found in the literature only above 77 K. In this high-temperature range the temperature dependence of B rad obtained using our combined sPL/MPL method is in good agreement with the available literature data for both samples. Interestingly, we have extended the measured range down to a temperature of 20 K and observed a strong increase of B rad by three orders of magnitude with decreasing temperature from 77 K to 20 K.
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Temperature dependence of the radiative Recombination Coefficient in crystalline silicon by spectral and modulated photoluminescence
physica status solidi (RRL) - Rapid Research Letters, 2017Co-Authors: Rudolf Brüggemann, José Alvarez, Mohamed Boutchich, Jean-paul KleiderAbstract:Phone: þ33 (0)169851645, Fax: þ33 (0)169418318 By the combination of temperature-dependent spectral photo-luminescence with modulated photoluminescence measurements the band-to-band radiative Recombination Coefficient is determined for crystalline silicon without the requirement to model the temperature dependence of the intrinsic carrier density, thus eliminating a source of error. By application of this approach we reproduce the variation of the radiative Recombination Coefficient in crystalline silicon with temperature reported in the literature for temperatures !77 K. Above all, we extend the measured range for the radiative Recombination Coefficient to a temperature of 20 K. In this extended temperature range between 20 and 70 K the Recombination Coefficient increases with decreasing temperature by about three orders of magnitude.
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Temperature dependence of the radiative Recombination Coefficient in crystalline silicon by spectral and modulated photoluminescence
physica status solidi (RRL) - Rapid Research Letters, 2017Co-Authors: Rudolf Brüggemann, José Alvarez, Mohamed Boutchich, Jean-paul KleiderAbstract:By the combination of temperature-dependent spectral photoluminescence with modulated photoluminescence measurements the band-to-band radiative Recombination Coefficient is determined for crystalline silicon without the requirement to model the temperature dependence of the intrinsic carrier density, thus eliminating a source of error. By application of this approach we reproduce the variation of the radiative Recombination Coefficient in crystalline silicon with temperature reported in the literature for temperatures ≥77 K. Above all, we extend the measured range for the radiative Recombination Coefficient to a temperature of 20 K. In this extended temperature range between 20 and 70 K the Recombination Coefficient increases with decreasing temperature by about three orders of magnitude.
Ronald Österbacka - One of the best experts on this subject based on the ideXlab platform.
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Two dimensional Langevin Recombination in regioregular poly(3-hexylthiophene)
Applied Physics Letters, 2009Co-Authors: Giedrius Juška, N. Nekrašas, G. Sliaužys, Kristijonas Genevičius, Ronald ÖsterbackaAbstract:In this work, it is shown that Recombination in regioregular poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (RRP3HT:PCBM) bulk-heterojunction solar cells is caused by the two dimensional (2D) Langevin Recombination in the lamellar structures of RRP3HT, which are formed after annealing process. Due to 2D Langevin process, bimolecular Recombination Coefficient is reduced in comparison with three dimensional Langevin case, and bimolecular Recombination Coefficient depends on the density of charge carriers n1/2. Data obtained from the different experimental techniques (charge extraction with linearly increasing voltage, integral time of flight, double injection current transients and transient absorption spectroscopy) confirms 2D Langevin Recombination in RR3PHT.
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Charge-carrier transport and Recombination in thin insulating films studied via extraction of injected plasma
Physical Review B, 2006Co-Authors: Giedrius Juška, Gilles Dennler, Kęstutis Arlauskas, G. Sliaužys, Almantas Pivrikas, Markus C. Scharber, Niyazi Serdar Sariciftci, Kristijonas Genevičius, Ronald ÖsterbackaAbstract:We show how charge-carrier transport and Recombination in thin insulator films are directly measured using the technique of extraction of injected plasma. This technically simple technique is complementary to the well-known time-of-flight technique. We use this technique on bulk-heterojunction solar cells, where the double-injection current into an insulator is found, and we show how to use the extraction of the injected plasma to independently and simultaneously measure the charge-carrier mobility and bimolecular Recombination Coefficient in these films. A simple analytical solution to calculate the bimolecular Recombination Coefficient from an injected charge is derived. We found that the extracted charge follows a linear dependence as a function of applied voltage and saturates as a function of offset voltage, leading to the conclusion that almost all of the injected charge is extracted at high offset voltages. Therefore, we can directly measure the charge-carrier mobility and bimolecular Recombination Coefficient from the extracted charge as a function of voltage pulse duration. Moreover, the charge-carrier bimolecular Recombination Coefficient $(\ensuremath{\beta}=2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}∕\mathrm{s})$ is found to be strongly reduced compared to Langevin-type Coefficient, as previously shown.
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Bimolecular Recombination Coefficient as a sensitive testing parameter for low-mobility solar-cell materials.
Physical review letters, 2005Co-Authors: Almantas Pivrikas, Attila J Mozer, Kęstutis Arlauskas, Giedrius Juška, Henrik Stubb, Markus C. Scharber, Niyazi Serdar Sariciftci, Ronald ÖsterbackaAbstract:Bimolecular charge carrier Recombination has been clarified in bulk-heterojunction solar cells based on a blend of regioregular poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-methanofullerene using the time-of-flight method. We show how bimolecular Recombination influences the charge carrier transport, how it limits the efficiency of low-mobility solar cells, and how to estimate the bimolecular Recombination Coefficient. We found that bimolecular Recombination in these efficient photovoltaic materials is orders of magnitude slower as compared to Langevin Recombination expected for low-mobility materials. This effect is inherent to the nanomorphology of the bicontinuous interpenetrating network creating separate pathways for electrons and holes, and paves the way for the fabrication of bulk-heterojunction solar cells where bimolecular Recombination is not the limiting factor.
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Optical studies of excited-state relaxation in poly(9,9-dihexylfluorene-co-benzothiadiazole)
Physical Review B, 2003Co-Authors: M. Westerling, Chellappan Vijila, Ronald Österbacka, Henrik StubbAbstract:We have studied the optical properties of poly(9,9-dihexylfluorene-co-benzothiadiazole) using absorption, photoluminescence as well, as cw and transient photoinduced absorption (PA) techniques. The PA spectrum shows a high-energy (HE) band peaked at 1.44 eV accompanied by shoulders on both sides. To study the Recombination kinetics of the photoexcitations associated with the HE band we measured the intensity and frequency dependence of the PA signal, and modeled the results by analytically solving the full bimolecular rate equation using harmonic analysis. As an important result of these calculations we found that the experimentally observed linear intensity dependence at low pump intensities can be explained by including a monomolecular term into the rate equation, in contrast to the superlinear intensity dependence predicted for pure bimolecular Recombination. Furthermore, the value of the monomolecular lifetime $\ensuremath{\tau}$ can directly be estimated from the ratio of the in-phase and out-of-phase signals in the linear regime, and we also show how to estimate the bimolecular Recombination Coefficient from the saturation value of the out-of-phase signal. To study the temperature dependence of the Recombination process we measured the transient decay of the HE band, and by fitting the results to the full bimolecular rate equation we extracted the temperature dependence of the amplitude, the monomolecular lifetime, and the bimolecular Recombination Coefficient. The monomolecular lifetime decreases almost linearly with increasing temperature, and the bimolecular Recombination Coefficient has a very strong non-Arrhenius temperature dependence i.e., $\ensuremath{\beta}={\ensuremath{\beta}}_{0}\mathrm{exp}[{(T/T}_{0}{)}^{2}],$ with ${\ensuremath{\beta}}_{0}=1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}{\mathrm{cm}}^{3}/\mathrm{s}$ and a characteristic temperature ${T}_{0}=82\mathrm{K}.$ A model for this unusual temperature dependence is proposed.
Rudolf Brüggemann - One of the best experts on this subject based on the ideXlab platform.
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radiative Recombination Coefficient in crystalline silicon at low temperatures 77 k by combined photoluminescence measurements
Energy Procedia, 2017Co-Authors: Rudolf Brüggemann, José Alvarez, Mohamed Boutchich, Jean-paul KleiderAbstract:Abstract Spectral photoluminescence (sPL) and modulated photoluminescence (MPL) measurements were applied to determine the band-to-band radiative Recombination Coefficient, Brad, in crystalline silicon. We used precursors of n-type crystalline silicon solar cells consisting of two different wafers passivated with aluminum oxide stacks or intrinsic hydrogenated amorphous silicon, respectively. So far values for Brad can be found in the literature only above 77 K. In this high-temperature range the temperature dependence of Brad obtained using our combined sPL/MPL method is in good agreement with the available literature data for both samples. Interestingly, we have extended the measured range down to a temperature of 20 K and observed a strong increase of Brad by three orders of magnitude with decreasing temperature from 77 K to 20 K.
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Radiative Recombination Coefficient in crystalline silicon at low temperatures < 77 K by combined photoluminescence measurements
Energy Procedia, 2017Co-Authors: Rudolf Brüggemann, José Alvarez, Mohamed Boutchich, Jean-paul KleiderAbstract:District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand-outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope Coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract Spectral photoluminescence (sPL) and modulated photoluminescence (MPL) measurements were applied to determine the band-to-band radiative Recombination Coefficient, B rad , in crystalline silicon. We used precursors of n-type crystalline silicon solar cells consisting of two different wafers passivated with aluminum oxide stacks or intrinsic hydrogenated amorphous silicon, respectively. So far values for B rad can be found in the literature only above 77 K. In this high-temperature range the temperature dependence of B rad obtained using our combined sPL/MPL method is in good agreement with the available literature data for both samples. Interestingly, we have extended the measured range down to a temperature of 20 K and observed a strong increase of B rad by three orders of magnitude with decreasing temperature from 77 K to 20 K.
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Temperature dependence of the radiative Recombination Coefficient in crystalline silicon by spectral and modulated photoluminescence
physica status solidi (RRL) - Rapid Research Letters, 2017Co-Authors: Rudolf Brüggemann, José Alvarez, Mohamed Boutchich, Jean-paul KleiderAbstract:Phone: þ33 (0)169851645, Fax: þ33 (0)169418318 By the combination of temperature-dependent spectral photo-luminescence with modulated photoluminescence measurements the band-to-band radiative Recombination Coefficient is determined for crystalline silicon without the requirement to model the temperature dependence of the intrinsic carrier density, thus eliminating a source of error. By application of this approach we reproduce the variation of the radiative Recombination Coefficient in crystalline silicon with temperature reported in the literature for temperatures !77 K. Above all, we extend the measured range for the radiative Recombination Coefficient to a temperature of 20 K. In this extended temperature range between 20 and 70 K the Recombination Coefficient increases with decreasing temperature by about three orders of magnitude.
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Temperature dependence of the radiative Recombination Coefficient in crystalline silicon by spectral and modulated photoluminescence
physica status solidi (RRL) - Rapid Research Letters, 2017Co-Authors: Rudolf Brüggemann, José Alvarez, Mohamed Boutchich, Jean-paul KleiderAbstract:By the combination of temperature-dependent spectral photoluminescence with modulated photoluminescence measurements the band-to-band radiative Recombination Coefficient is determined for crystalline silicon without the requirement to model the temperature dependence of the intrinsic carrier density, thus eliminating a source of error. By application of this approach we reproduce the variation of the radiative Recombination Coefficient in crystalline silicon with temperature reported in the literature for temperatures ≥77 K. Above all, we extend the measured range for the radiative Recombination Coefficient to a temperature of 20 K. In this extended temperature range between 20 and 70 K the Recombination Coefficient increases with decreasing temperature by about three orders of magnitude.
Karol Hensel - One of the best experts on this subject based on the ideXlab platform.
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Dependence of the dissociative Recombination Coefficient of molecular ions ${\rm Kr}_2^+$ with electrons on the electron and gas temperatures
Plasma Sources Science and Technology, 2012Co-Authors: P. Lukáč, O Mikus, I Morva, Z Zábudlá, J. Trnovec, Marcela Morvová, Karol HenselAbstract:This paper presents the measured values of the dissociative Recombination Coefficient of molecular ions with electrons α as a function of both electron and gas temperatures. The measurements were made using a dual-mode (waveguide-cavity) microwave X-band apparatus. The Recombination Coefficient can be expressed as in the temperature ranges 300 K ⩽ Tgas ⩽ 500 K and 300 K ⩽ Te ⩽ 19 000 K.
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dependence of the dissociative Recombination Coefficient of molecular ions rm kr _2 with electrons on the electron and gas temperatures
Plasma Sources Science and Technology, 2012Co-Authors: P. Lukáč, O Mikus, I Morva, Z Zábudlá, J. Trnovec, Marcela Morvová, Karol HenselAbstract:This paper presents the measured values of the dissociative Recombination Coefficient of molecular ions with electrons α as a function of both electron and gas temperatures. The measurements were made using a dual-mode (waveguide-cavity) microwave X-band apparatus. The Recombination Coefficient can be expressed as in the temperature ranges 300 K ⩽ Tgas ⩽ 500 K and 300 K ⩽ Te ⩽ 19 000 K.
