Lawrence L. Kazmerski

Effects of CdCl2 treatment on the recrystallization and electro-optical properties of CdTe thin films

The effects of CdCl2 processing on the physical and electro-optical properties of CdTe were evaluated for thin films produced by physical vapor deposition and close-spaced sublimation (CSS). Two substrates (CdS and Indium–tin–oxide) were used with the physical vapor deposition (PVD) films specifically to isolate the effects of the Cd(SxTe1−x) alloy formed during the treatment of films deposited on CdS. The samples were analyzed by x-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence. The observed changes in microstructure were caused by recrystallization, which consisted of the nucleation and development of a new CdTe structure and subsequent grain growth. Nevertheless, for these processes to take place, it was necessary that enough lattice-strain energy was available in the films. For this reason, PVD films did recrystallize, while CSS films did not. For the first time, recrystallization was observed directly in AFM images of CdTe films and confirmed by XRD analysis, which indica...

Photovoltaics: A review of cell and module technologies

This review centers on the status, and future directions of the cell and module technologies, with emphasis on the research and development aspects. The framework is established with a consideration of the historical parameters of photovoltaics and each particular technology approach. The problems and strengths of the single-crystal, polycrystalline, and amorphous technologies are discussed, compared, and assessed. Single- and multiple junction or tandem cell configurations are evaluated for performance, processing, and engineering criteria. Thin-film technologies are highlighted as emerging, low-cost options for terrestrial applications and markets. Discussions focus on the fundamental building block for the photovoltaic system, the solar cell, but important module developments and issues are cited. Future research and technology directions are examined, including issues that are considered important for the development of the specific materials, cell, and module approaches. Novel technologies and new research areas are surveyed as potential photovoltaic options of the future.

Photovoltaics gaining greater visibility

Photovoltaics technology is well established as a reliable and economical source of electricity in small, scattered applications, far from urban centers. Now it is looming larger in size and public awareness. The author discusses the role of photovoltaic systems in the USA, their operating principles and developments for the future.

Investigation of polycrystalline CdTe thin films deposited by physical vapor deposition, close‐spaced sublimation, and sputtering

CdTe thin films, deposited on different substrate structures by physical vapor deposition, sputtering, and close‐spaced sublimation, have been treated with CdCl2 at several temperatures. The morphology of the films has been studied by atomic force microscopy, and the observations were correlated to results obtained from x‐ray diffraction, cathodoluminescence, and minority‐carrier lifetime measurements. The samples treated at 400 °C resulted in the best device‐quality films, independent of deposition method and underlying substrate structure. For the first time, a nanograin structure was observed in CdTe sputtered samples.CdTe thin films, deposited on different substrate structures by physical vapor deposition, sputtering, and close‐spaced sublimation, have been treated with CdCl2 at several temperatures. The morphology of the films has been studied by atomic force microscopy, and the observations were correlated to results obtained from x‐ray diffraction, cathodoluminescence, and minority‐carrier lifetime measurements. The samples treated at 400 °C resulted in the best device‐quality films, independent of deposition method and underlying substrate structure. For the first time, a nanograin structure was observed in CdTe sputtered samples.

INVESTIGATION OF INDUCED RECRYSTALLIZATION AND STRESS IN CLOSE-SPACED SUBLIMATED AND RADIO-FREQUENCY MAGNETRON SPUTTERED CDTE THIN FILMS

We have induced recrystallization of small grain CdTe thin films deposited at low temperatures by close-spaced sublimation (CSS), using a standard CdCl2 annealing treatment. We also studied the changes in the physical properties of CdTe films deposited by radio-frequency magnetron sputtering after the same post-deposition processing. We demonstrated that the effects of CdCl2 on the physical properties of CdTe films are similar, and independent of the deposition method. The recrystallization process is linked directly to the grain size and stress in the films. These studies indicated the feasibility of using lower-temperature processes in fabricating efficient CSS CdTe solar cells. We believe that, after the optimization of the parameters of the chemical treatment, these films can attain a quality similar to CSS films grown using current standard conditions.

Renewable Energy Sources and Climate Change Mitigation: Direct Solar Energy

Executive Summary Solar energy is abundant and offers significant potential for near-term (2020) and long-term (2050) climate change mitigation. There are a wide variety of solar technologies of varying maturities that can, in most regions of the world, contribute to a suite of energy services. Even though solar energy generation still only represents a small fraction of total energy consumption, markets for solar technologies are growing rapidly. Much of the desirability of solar technology is its inherently smaller environmental burden and the opportunity it offers for positive social impacts. The cost of solar technologies has been reduced significantly over the past 30 years and technical advances and supportive public policies continue to offer the potential for additional cost reductions. Potential deployment scenarios range widely—from a marginal role of direct solar energy in 2050 to one of the major sources of energy supply. The actual deployment achieved will depend on the degree of continued innovation, cost reductions and supportive public policies. Solar energy is the most abundant of all energy resources . Indeed, the rate at which solar energy is intercepted by the Earth is about 10,000 times greater than the rate at which humankind consumes energy. Although not all countries are equally endowed with solar energy, a significant contribution to the energy mix from direct solar energy is possible for almost every country. Currently, there is no evidence indicating a substantial impact of climate change on regional solar resources.

Photovoltaics R&D: At the Tipping Point

Publisher Summary The future investments for photovoltaics research and development are contemplated for this new millennium. Current technologies are used as the foundation for what might be expected for the next 50 years. A “tour” is conducted through which the coming generations can anticipate for the technology emphasizing nonconventional applications beyond the “expected.” Next-generation research approaches are predicted indicating the horizon of PV technology. Conjectures of those PV and related technologies that are beyond the horizon are presented with prognosis on the coming generations that might have their “conventional” energy sources. Photovoltaics research and development is addressed in three temporal segments, dividing the century into the immediate term (2000–2015), the intermediate term (2010–2025), and the far-term (2020–2050 and beyond).

Renewable Energy Opportunities in Water Desalination

Desalination is a water-treatment process that separates salts from saline water to produce potable water or water that is low in total dissolved solids (TDS). Globally, the total installed capacity of desalination plants was 61 million m3 per day in 2008 [1]. Seawater desalination accounts for 67% of production, followed by brackish water at 19%, river water at 8%, and wastewater at 6%. Figure 1 show the worldwide feed-water percentage used in desalination. The most prolific users of desalinated water are in the Arab region, namely, Saudi Arabia, Kuwait, United Arab Emirates, Qatar, Oman, and Bahrain [2].

Alternative procedure for the fabrication of close-spaced sublimated CdTe solar cells

We deposited CdTe thin films by close-spaced sublimtation using an alternative procedure, with temperatures about 170 °C lower than the ones used in the standard procedure. These films were used in the fabrication of all thin-film CdTe/CdS solar cells. We treated the cells using the well-established CdCl2 dipping process as well as a new vapor treatment. The vapor process was more reproducible and easier to control, and it produced the best devices. This process was also much more effective in the recrystallization of the CdTe films. The best device that we produced had an efficiently of 11.6%, close to the 12.3% efficiency of the best device fabricated using the standard process. These results show that the new process has good potential, and besides being an alternative for lower-cost solar cell production, it can also produce high-efficiency devices.

Micro through nanostructure investigations of polycrystalline CdTe: Correlations with processing and electronic structures

Abstract This paper provides first-time correlations of the nanoscale physical structure with the macroscale electronic and optical properties of CdTe/CdS thin films for several standard deposition techniques. Atomic force microscopy (AFM) was used to determine the micro and nanostructures of polycrystalline CdTe thin films used in photovoltaic (PV) cell fabrication. Photoluminescence (PL) was used to determine band gap, relative defect density, and photoexcited carrier lifetime. Cross-sectional scanning tunneling microscopy (STM) was used to determine the nanoscale electronic properties. Nanostructural features (nanograins), beyond the spatial resolution of conventional scanning electron microscopy (SEM), were observed and characterized in as-deposited CdTe. The correlations of the proximal probe measurements of the physical and electronic structure with the optically determined electronic properties were used to show the effects of the chemical and heat processing, directly and conclusively. A particularly striking effect with important implications for PV applications is the diffusion of sulfur across the CdTe/CdS interface during heat treatment.