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12. Energy and environment in the ASEAN: challenges and opportunities

Author

Karki, Shankar K., Mann, Michael D., and Salehfar, Hossein

Subjects
Power resources -- Analysis, Power resources -- Management, Company business management, Business, Environmental issues, Petroleum, energy and mining industries, Association of Southeast Asian Nations -- Economic aspects
Abstract

The rapid advancement of the economy in the ASEAN (The Association of Southeast Asian Nations) region has brought with it concerns of the depleting energy resources. Urgent steps need to be taken in energy resource management and to exploit renewable energy resources like hydro to cope with the future demand.

Published
2005

18. Effect of Alkali on the Efficiency and Reliability of Cu(In,Ga)Se2 Solar Cells

Author

Karki, Shankar

Abstract

The incorporation of alkali metal has contributed tremendously in a bid to realize greater than 20% efficient Cu(In,Ga)Se2(CIGS) solar cells. Achieving high efficiency is one key parameter for the success of a photovoltaic technology but so is its long-term stability. In this thesis, the relationship between the performance of alkali treated Cu(In,Ga)Se2 solar cells and their physicochemical, electronic and structural properties are explored through a comparative study between standard devices and alkali (K, Rb) treated devices. The alkali treated devices tend to have a lower concentration of Ev+0.98 eV trap, higher majority carrier concentration and improved minority carrier lifetime, contributing to the experimentally observed improvement in open circuit voltage. Critical changes in alkali elemental profile occur throughout the film, while no other major physicochemical or structural properties are modified. Furthermore, we explored the long-term stability of CIGS solar cells due to damp heat treatment. We specifically study the influence on the molybdenum back contact and the CIGS absorber layer itself, with an emphasis on the role played by sodium. Molybdenum thin films showed drastic micro-structural, surface morphology, electrical and optical properties deterioration leading to the degradation of solar cell performance. In the case of bare CIGS thin films, we observed surface oxidation and degraded electronic properties, also leading to degradation of the solar cell performance. In both cases, alkali migration is responsible for the most part of the degradation, along with surface oxidation.

Published
2019
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19. Degradation Mechanism in Cu(In,Ga)Se2 Material and Solar Cells Due to Moisture and Heat Treatment of the Absorber Layer

Author

Karki, Shankar, primary, Paul, Pran, additional, Deitz, Julia I., additional, Poudel, Deewakar, additional, Rajan, Grace, additional, Belfore, Benjamin, additional, Danilov, Evgeny O., additional, Castellano, Felix N., additional, Grassman, Tyler J., additional, Arehart, Aaron, additional, Rockett, Angus, additional, and Marsillac, Sylvain, additional

Published
2019
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39. In Situ and Ex Situ Investigations of KF Postdeposition Treatment Effects on CIGS Solar Cells

Author

Karki, Shankar, primary, Paul, Pran K., additional, Rajan, Grace, additional, Ashrafee, Tasnuva, additional, Aryal, Krishna, additional, Pradhan, Puja, additional, Collins, Robert Warren, additional, Rockett, Angus, additional, Grassman, Tyler J., additional, Ringel, Steven A., additional, Arehart, Aaron R., additional, and Marsillac, Sylvain, additional

Published
2017
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45. Impact of Water Ingress on Molybdenum Thin Films and Its Effect on Cu(In,Ga)Se2 Solar Cells

Author

Karki, Shankar, Deitz, Julia I., Rajan, Grace, Soltanmohammad, Sina, Poudel, Deewakar, Belfore, Benjamin, Bhandari, Gandhari, Grassman, Tyler J., Rockett, Angus, and Marsillac, Sylvain

Abstract

Solar cell degradation can occur through many pathways and at the different stages of the fabrication process, notably because of the water condensation. In the case of Cu(In,Ga)Se2 (CIGS) solar cells, the impact of water ingress on Mo back contact can be substantial for not only the film itself but also the device performance and reliability. Microstructural modification, change in film morphology, loss in reflectance, and increased resistivity because of the moisture ingress were observed via X-ray diffraction, transmission electron microscopy, spectroscopic ellipsometry, and four-point probe measurements, respectively. Secondary ion mass spectrometry measurements revealed drastic changes in the alkali (Na, K) profiles in both the CIGS and Mo layers, likely because of the modification of their diffusion coefficient through Mo. This, in turn, negatively impacts the solar cell efficiency by decreasing both fill factor and open-circuit voltage. Additional experiments, modifying the substrate and utilizing a NaF postdeposition treatment, highlight the mechanisms of degradation as being due to both a modification of the Mo/CIGS interface and the lack of alkali diffusion after water ingress.

Published
2020
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48. Degradation Mechanism in Cu(In,Ga)Se2 Material and Solar Cells Due to Moisture and Heat Treatment of the Absorber Layer

Author

Karki, Shankar, Paul, Pran, Deitz, Julia I., Poudel, Deewakar, Rajan, Grace, Belfore, Benjamin, Danilov, Evgeny O., Castellano, Felix N., Grassman, Tyler J., Arehart, Aaron, Rockett, Angus, and Marsillac, Sylvain

Abstract

The impact of moisture and heat treatment on the microstructural, chemical, and electrical properties of Cu(In,Ga)Se2 films and their collective effect on the solar cell device performance was studied. X-ray photoelectron spectroscopy and secondary ion mass spectroscopy measurements show that water exposure causes surface modification and alters the alkali metal distribution, while no composition or structural effect was observed. Deep level transient and optical spectroscopies revealed that the trap densities (NT) for both the EV + 0.65 eV and EV + 0.98 eV traps increase after water exposure, while the majority carrier concentration (NA) decreases. Time-resolved photoluminescence (PL) and steady-state PL measurements indicated the presence of static, not dynamic, quenching. Reduction of open-circuit voltage (VOC) and fill factor (FF) was observed for the devices but was not associated with a change of recombination mechanism, which remains in the absorber space charge region. A small increase in series resistance and shunt conductance accounts for most of the FF change, while the modification in both NA and NT yield most of the change in VOC. A gradient of majority carrier concentration, related to the alkali profile, also yields a small voltage-dependent current collection after moisture and heat treatment.

Published
2019
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50. Substitution and price effects of carbon emission penalties on C[O.sub.2] emissions reduction from electric power plants

Author

Karki, Shankar, Mann, Michael D., and Salehfar, Hossein

Subjects
Power plants -- Environmental aspects, Electric power-plants -- Environmental aspects, Carbon -- Environmental aspects -- Prices and rates, Protocol to the Framework Convention on Climate Change, 1997, Science and technology, Company pricing policy, Prices and rates, Environmental aspects
Abstract

Eight years after its inception, the Kyoto Protocol finally entered into force on February 16, 2005. In this respect, it is imperative to explore different greenhouse gas (GHGs) emissions reduction [...]

Published
2005

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