Asha Rao - Academia.edu (original) (raw)

Papers by Asha Rao

Research paper thumbnail of Capacitance and conductance studies on silicon solar cells subjected to 8MeV electron irradiations

Radiation Physics and Chemistry, 2015

The space grade silicon solar cells were irradiated with 8 MeV electrons with doses ranging from ... more The space grade silicon solar cells were irradiated with 8 MeV electrons with doses ranging from 5 kGy-100 kGy. Capacitance and conductance measurements were carried out in order to investigate the anomalous degradation of the cells in the radiation harsh environments and the results are presented in this paper. Detailed and systematic analysis of the frequency-dependent capacitance and conductance measurements were performed to extract the information about the interface trap states. The small increase in density of interface states was observed from the conductancefrequency measurements. The reduction in carrier concentration upon electron irradiation is due to the trapping of charge carriers by the radiation induced trap centres. The Drive Level Capacitance Profiling (DLCP) technique has been applied to study the properties of defects in silicon solar cells. The small variation in responding state densities with measuring frequency was observed and the defect densities are in the range 10 15 cm-3 to 10 16 cm-3 .

Research paper thumbnail of A study on the variation of c-Si solar cell parameters under 8MeV electron irradiation

Solar Energy Materials and Solar Cells, 2014

ABSTRACT This paper reports on the photon and 8 MeV electron irradiation effects on electrical pa... more ABSTRACT This paper reports on the photon and 8 MeV electron irradiation effects on electrical parameters, quantum efficiency and minority carrier lifetime of a c-Si solar cell.The effect of subsequent photon irradiation on the silicon solar cells,degraded by 8MeV electron irradiation is also investigated. The current–voltage(I–V) characteristics of solar cells under AM0 illumination condition were studied before and after the irradiation. The solar cell parameters such as short circuit current (Isc), open circuit voltage (Voc), fill factor (FF), and conversion efficiency (η) were found to decrease after electron irradiation. A slight improvement in the electric performance of solar cells is observed after the photon irradiation. The spectral response shows that the quantum efficiency for lower energy photons is reduced, suggesting that the damage is mainly inflicted to the bulk of the absorber material. This is strongly supported by the minority carrier life time results, which show a clear trend of decreasing carrier lifetime and carrier diffusion length as radiation dose increases.

Research paper thumbnail of Measurement of Variation of Minority Carrier Lifetime in 8 MeV Electron Irradiated c-Si Solar Cells Using RRT Method

Environmental Science and Engineering, 2013

ABSTRACT The variation of minority carrier lifetime in c- Si solar cells due to the irradiation o... more ABSTRACT The variation of minority carrier lifetime in c- Si solar cells due to the irradiation of 8MeV electrons of various doses ranging from 5 kGy to 100 kGy was studied. The minority carrier lifetime and diffusion length of c-Si solar cells were determined before and after irradiation using the reverse recovery transient (RRT) method. The minority carrier lifetime is found to decrease with increasing electron dose, which is interpreted as due to the creation of non-radiative recombination centers which affects the diffusion current. The minority carrier diffusion length decreases exponentially with electron dose. The reduction in diffusion length due to electron irradiation will reduce the conversion efficiency of solar cells.

Research paper thumbnail of 8MeV electron irradiation studies on electrical characteristics of Cu(In,Ga)Se2 solar cells

Solar Energy Materials and Solar Cells, 2009

Cu(In,Ga)Se 2 (CIGS) solar cells are gaining considerable interest due to their high optical abso... more Cu(In,Ga)Se 2 (CIGS) solar cells are gaining considerable interest due to their high optical absorption coefficient and adjustable band gap, which enables them to achieve high conversion efficiency and also present many promising applications in space power systems. In this paper we report the results of the effect of temperature and 8 MeV electron irradiation on the electrical characteristics of ZnO/CdS/ Cu(In,Ga)Se 2 /Mo polycrystalline thin-film solar cells under forward and reverse bias studied in the temperature range 270-315 K. The solar cells were subjected to 8 MeV electron irradiation from the Microtron accelerator and were exposed to graded doses of electrons up to 75 kGy. I-V characteristics of the cells under dark and AM 1.5 illumination condition were studied before and after the irradiation. Capacitance measurements were also carried out at various frequencies before and after irradiation. In the measured temperature range, the dark current contribution is due to the generation-recombination of the minority carriers in the depletion region. The ideality factor is found to decrease with increase in temperature. It seems that electron irradiation has not altered the dark current conduction mechanism significantly. The effect of electron irradiation on the solar cell parameters such as fill factor (FF), conversion efficiency (Z), saturation current (I o), short circuit current (I sc), open circuit voltage (V oc), and ideality factor (n) was studied. They were found to be stable up to 75 kGy of electron dose as only small changes were observed in the solar cell parameters.

Research paper thumbnail of Temperature and 8 MeV electron irradiation effects on GaAs solar cells

Pramana, 2010

GaAs solar cells hold the record for the highest single band-gap cell efficiency. Successful appl... more GaAs solar cells hold the record for the highest single band-gap cell efficiency. Successful application of these cells in advanced space-borne systems demand characterization of cell properties like dark current under different ambient conditions and the stability of the cells against particle irradiation in space. In this paper, the results of the studies carried out on the effect of 8 MeV electron irradiation on the electrical properties of GaAs solar cells are presented. The I-V (current-voltage) characteristics of the cells under dark and AM1.5 illumination condition are studied and 8 MeV electron irradiation was carried out on the cells where they were exposed to graded doses of electrons from 1 to 100 kGy. The devices were also characterized using capacitance measurements at various frequencies before and after irradiation. The effect of electron irradiation on the solar cell parameters was studied. It is found that only small changes were observed in the GaAs solar cell parameters up to an electron dose of 100 kGy, exhibiting good tolerance for electrons of 8 MeV energy.

Research paper thumbnail of Variation of carrier concentration and interface trap density in 8MeV electron irradiated c-Si solar cells

ABSTRACT The capacitance and conductance measurements were carried out for c-Si solar cells, irra... more ABSTRACT The capacitance and conductance measurements were carried out for c-Si solar cells, irradiated with 8 MeV electrons with doses ranging from 5kGy - 100kGy in order to investigate the anomalous degradation of the cells in the radiation harsh environments. Capacitance - Voltage measurements indicate that there is a slight reduction in the carrier concentration upon electron irradiation due to the creation of radiation induced defects. The conductance measurement results reveal that the interface state densities and the trap time constant increases with electron dose due to displacement damages in c-Si solar cells.

Research paper thumbnail of Capacitance and conductance studies on silicon solar cells subjected to 8MeV electron irradiations

Radiation Physics and Chemistry, 2015

The space grade silicon solar cells were irradiated with 8 MeV electrons with doses ranging from ... more The space grade silicon solar cells were irradiated with 8 MeV electrons with doses ranging from 5 kGy-100 kGy. Capacitance and conductance measurements were carried out in order to investigate the anomalous degradation of the cells in the radiation harsh environments and the results are presented in this paper. Detailed and systematic analysis of the frequency-dependent capacitance and conductance measurements were performed to extract the information about the interface trap states. The small increase in density of interface states was observed from the conductancefrequency measurements. The reduction in carrier concentration upon electron irradiation is due to the trapping of charge carriers by the radiation induced trap centres. The Drive Level Capacitance Profiling (DLCP) technique has been applied to study the properties of defects in silicon solar cells. The small variation in responding state densities with measuring frequency was observed and the defect densities are in the range 10 15 cm-3 to 10 16 cm-3 .

Research paper thumbnail of A study on the variation of c-Si solar cell parameters under 8MeV electron irradiation

Solar Energy Materials and Solar Cells, 2014

ABSTRACT This paper reports on the photon and 8 MeV electron irradiation effects on electrical pa... more ABSTRACT This paper reports on the photon and 8 MeV electron irradiation effects on electrical parameters, quantum efficiency and minority carrier lifetime of a c-Si solar cell.The effect of subsequent photon irradiation on the silicon solar cells,degraded by 8MeV electron irradiation is also investigated. The current–voltage(I–V) characteristics of solar cells under AM0 illumination condition were studied before and after the irradiation. The solar cell parameters such as short circuit current (Isc), open circuit voltage (Voc), fill factor (FF), and conversion efficiency (η) were found to decrease after electron irradiation. A slight improvement in the electric performance of solar cells is observed after the photon irradiation. The spectral response shows that the quantum efficiency for lower energy photons is reduced, suggesting that the damage is mainly inflicted to the bulk of the absorber material. This is strongly supported by the minority carrier life time results, which show a clear trend of decreasing carrier lifetime and carrier diffusion length as radiation dose increases.

Research paper thumbnail of Measurement of Variation of Minority Carrier Lifetime in 8 MeV Electron Irradiated c-Si Solar Cells Using RRT Method

Environmental Science and Engineering, 2013

ABSTRACT The variation of minority carrier lifetime in c- Si solar cells due to the irradiation o... more ABSTRACT The variation of minority carrier lifetime in c- Si solar cells due to the irradiation of 8MeV electrons of various doses ranging from 5 kGy to 100 kGy was studied. The minority carrier lifetime and diffusion length of c-Si solar cells were determined before and after irradiation using the reverse recovery transient (RRT) method. The minority carrier lifetime is found to decrease with increasing electron dose, which is interpreted as due to the creation of non-radiative recombination centers which affects the diffusion current. The minority carrier diffusion length decreases exponentially with electron dose. The reduction in diffusion length due to electron irradiation will reduce the conversion efficiency of solar cells.

Research paper thumbnail of 8MeV electron irradiation studies on electrical characteristics of Cu(In,Ga)Se2 solar cells

Solar Energy Materials and Solar Cells, 2009

Cu(In,Ga)Se 2 (CIGS) solar cells are gaining considerable interest due to their high optical abso... more Cu(In,Ga)Se 2 (CIGS) solar cells are gaining considerable interest due to their high optical absorption coefficient and adjustable band gap, which enables them to achieve high conversion efficiency and also present many promising applications in space power systems. In this paper we report the results of the effect of temperature and 8 MeV electron irradiation on the electrical characteristics of ZnO/CdS/ Cu(In,Ga)Se 2 /Mo polycrystalline thin-film solar cells under forward and reverse bias studied in the temperature range 270-315 K. The solar cells were subjected to 8 MeV electron irradiation from the Microtron accelerator and were exposed to graded doses of electrons up to 75 kGy. I-V characteristics of the cells under dark and AM 1.5 illumination condition were studied before and after the irradiation. Capacitance measurements were also carried out at various frequencies before and after irradiation. In the measured temperature range, the dark current contribution is due to the generation-recombination of the minority carriers in the depletion region. The ideality factor is found to decrease with increase in temperature. It seems that electron irradiation has not altered the dark current conduction mechanism significantly. The effect of electron irradiation on the solar cell parameters such as fill factor (FF), conversion efficiency (Z), saturation current (I o), short circuit current (I sc), open circuit voltage (V oc), and ideality factor (n) was studied. They were found to be stable up to 75 kGy of electron dose as only small changes were observed in the solar cell parameters.

Research paper thumbnail of Temperature and 8 MeV electron irradiation effects on GaAs solar cells

Pramana, 2010

GaAs solar cells hold the record for the highest single band-gap cell efficiency. Successful appl... more GaAs solar cells hold the record for the highest single band-gap cell efficiency. Successful application of these cells in advanced space-borne systems demand characterization of cell properties like dark current under different ambient conditions and the stability of the cells against particle irradiation in space. In this paper, the results of the studies carried out on the effect of 8 MeV electron irradiation on the electrical properties of GaAs solar cells are presented. The I-V (current-voltage) characteristics of the cells under dark and AM1.5 illumination condition are studied and 8 MeV electron irradiation was carried out on the cells where they were exposed to graded doses of electrons from 1 to 100 kGy. The devices were also characterized using capacitance measurements at various frequencies before and after irradiation. The effect of electron irradiation on the solar cell parameters was studied. It is found that only small changes were observed in the GaAs solar cell parameters up to an electron dose of 100 kGy, exhibiting good tolerance for electrons of 8 MeV energy.

Research paper thumbnail of Variation of carrier concentration and interface trap density in 8MeV electron irradiated c-Si solar cells

ABSTRACT The capacitance and conductance measurements were carried out for c-Si solar cells, irra... more ABSTRACT The capacitance and conductance measurements were carried out for c-Si solar cells, irradiated with 8 MeV electrons with doses ranging from 5kGy - 100kGy in order to investigate the anomalous degradation of the cells in the radiation harsh environments. Capacitance - Voltage measurements indicate that there is a slight reduction in the carrier concentration upon electron irradiation due to the creation of radiation induced defects. The conductance measurement results reveal that the interface state densities and the trap time constant increases with electron dose due to displacement damages in c-Si solar cells.