This project aims to develop a unique class of inorganic-organic hybrid semiconductors with strong potential for photovoltaic applications. These materials can be considered as derivatives of II-VI based wide-bandgap hybrid systems, and will be designed to have systematically tunable crystal structures, compositions and semiconductor properties, with band gaps falling in a range specifically suitable for use in solar cells. These crystalline materials are composed of semiconductor motifs of identical size (e.g. chains, single-layer and multi-layer slabs), which are arranged into perfectly ordered arrays via chemical bonds with organic spacers. They demonstrate unusual and numerous enhanced electronic and optical properties that are not achievable in their semiconductor parent bulk, as a result of strong structure-induced quantum confinement. The goal is to research fundamental questions concerning the chemistry and physics occurring at the inorganic-organic interface, which will assist in-depth understanding of the structure-composition-property relationship, and offer guidance to future development of hybrid materials with unique properties. Important educational aspects of this project include strong commitment to student training.
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Seeking affordable, clean, and efficient energy to replace fossil fuels has become a major global effort to reduce emission of green house gases. Sunlight is a widely available renewable energy source and photovoltaics (PV) is an important power-generating technology that converts sunlight directly into electricity. This research project will provide semiconductor materials with improved performance for solar energy conversion technologies. The materials will be made of both inorganic and organic components, and the blending of the two will lead to a number of enhanced functionalities. By modifying their structures and compositions one can systematically tune the properties of these hybrid semiconductors to increase energy efficiency. The impact of this project is both educational and technological. From an educational point of view, this project will provide unique opportunities for graduate and undergraduate students to directly participate in energy research, and as a result of the involvement of the PI in several campus- and university-wide centers and programs at Rutgers, such as the Institute of Advanced Materials, Devices and Nanotechnology (IAMDN), an Energy Research Initiative (ERI), two NSF funded Interdisciplinary Graduate Education and Research Training (IGERT) programs, and Engineering Research Center (ERC), a more general training and education will be available to students supported under this grant.
Inorganic-organic hybrid semiconductors represent an important family of advanced materials that are of both fundamental and practical relevance. These materials have attracted enormous attention because of their strong capability in achieving integrated and enhanced properties that are not easily attainable with either organic or inorganic compound alone. Thus, the intrinsic functionality of the individual components, such as excellent electronic, magnetic and optical properties, structural integrity and thermal stability of the inorganic counterpart, and structural diversity, flexibility, processability, low-cost and light-weight of the organic counterpart, are retained in the resultant composite phases. In addition, such integration may not only lead to enhanced and improved chemical and physical properties, but very often, also introduce new features and novel phenomena that are not possible with either organic or inorganic component alone. We have developed unique nanostructured inorganic-organic hybrid semiconductors. These crystalline materials are built on nano- or subnano-modules of binary semiconductors with general formula of MQ (M = Zn, Cd, Mn; and Q = S, Se, Te) or MnQl (M = In, Sb, Bi) as the inorganic component and amine molecules as the organic component. The two modules are arranged via self-assembly processes into perfectly ordered and alternating arrays of extended crystal structures. In the cases of MQ based hybrid structures the semiconductor segments have the same (or little perturbed) crystal structure, composition, oxidation state, and chemical bonding as in their parent MQ phases, all important semiconductor properties are thus preserved. These materials have relatively large and widely tunable band gaps that are desirable for optical applications. In the cases of MnQl based hybrid structures, lower band gaps are achieved, making them particularly suitable for photovoltaic devices. By varying the chemical compositions and reaction conditions, we have synthesized and structurally characterized many new compounds. Investigations of their properties reveal that these hybrid semiconductors show a number of integrated and improved properties over their parent binary semiconductors. For example, their optical absorption and emission power are significantly enhanced, placing them among the most efficient light absorbing/emitting semiconductor materials. The introduction of organic interface into the semiconductor crystal structures gives rise to substantially reduced thermal conductivity, lower weight (material density) and higher flexibility. The blending of the inorganic and organic components at the atomic and molecular level also leads to unique phenomena and new functionality. These include the white light emission by the double-layer hybrid compounds. Such a behavior is distinctly different from their parent semiconductors such as ZnS that emits blue light. In fact, these hybrid compounds represent the first examples of single-phased and rare-earth metal free semiconductor white light phosphors in bulk form. In addition, they exhibit nearly zero thermal expansion which is not possible with a single component. A large number of postdoctoral associates, graduate and undergraduate students, visiting scholars and high school students have participated in this project. The highly interdisciplinary research has also stimulated strong collaborations and attracted collaborators in various fields, including chemistry, physics, materials science and engineering, within and outside the United States. Eighteen journal publications and four book chapters and review articles have resulted from this program. The PI has actively participated in educational and outreach activities at all levels. The establishment on high quantum efficiency lanthanide-free white light phosphors has caught strong interest of lighting industries. Two patents are filed and work is currently in progress for possible implementation of the next phase development.
