| Description | Perovskite quantum dots: a new absorber technology with unique phase properties for high voltage solar cells
Abstract: The newly rediscovered perovskite semiconductor system has the potential to be extremely transformative for all optoelectronic devices, especially photovoltaics (PVs). Perovskite semiconductors of the form APbI3 where A is a large +1 charged cation, typically Cs, methylammonium, or formamidinium have had a huge resurgence among materials scientists for outstanding PV properties despite being overlooked for decades. Semiconductors containing the latter two A-site cations listed are hybrid organic-inorganic materials, and as such, are far less understood compared to conventional all inorganic or even organic material systems. Regardless of this spotty formal understanding, lead-halide perovskites have very rapidly been optimized to power conversion efficiency levels on par with all other materials even with extensive history of research. Perovskites show a unique tolerance to crystalline defects that cause trouble in most other semiconductors. Therefore the potential offered is that very high efficiency PVs can be fabricated in extremely fast and inexpensive ways, thus offering a revolution for the solar industry and a direct route toward producing the world’s energy with a simple and clean technology. Long-term durability of the devices is the critical remaining challenge to be solved. Two examples of major instabilities in device performance are the volatility of the organic cation and the specific crystal habit in which the material embodies.
Nanoscale versions (often termed quantum dots (QDs)) of the all-inorganic metal halide perovskite (CsPbI3) tend to retain the desired cubic phase due to strain effects at the surface of the QDs whereas conventional films of the same material “relax” to an orthorhombic structure at room temperature. Therefore these QDs potentially solve both of the instability issues. The cubic CsPbI3 QD cells operate with a rather remarkable open-circuit voltage of >1.2 volts and have produced power conversion efficiencies over 13%. This customizable new nanomaterial system has incredible potential for many applications in optoelectronics, including photovoltaics, LEDs, displays and lasers. We describe the formation of α-CsPbI3 QD films with long range electronic transport that retain the high temperature phase in ambient conditions making up the active layer in optoelectronic devices. Perspectives on how this technology can become transformative will be discussed. Bio: Joseph M. Luther has been a senior research scientist in the Chemistry and Nanoscience division of Materials and Chemical Science and Technology directorate at the National Renewable Energy Laboratory (NREL) since 2009. His current area of focus is optoelectronic device applications employing novel semiconductor systems such as metal-halide perovskites and colloidal quantum dots. Research along these lines includes solution based growth mechanics, chemistry, electronic transport phenomena, interfaces, prototype photovoltaic and other device development. He obtained B.S. degrees in Electrical and Computer Engineering from North Carolina State University in 2001. At NCSU he began his research career under the direction of Salah Bedair, who was the first to fabricate a tandem junction solar cell. Luther worked on growth and characterization of high-efficiency III-V materials including GaN and GaAsN. His interest in photovoltaics sent him to the National Renewable Energy Laboratory (NREL) to pursue graduate work. He obtained a Masters of Science in Electrical Engineering from the University of Colorado while researching effects of defects in bulk semiconductors in NREL’s Measurements and Characterization Division. In 2005, he joined Art Nozik’s group at NREL to study semiconductor nanocrystals for multiple exciton generation for which he was awarded a Ph.D. in Physics from Colorado School of Mines. As a postdoctoral fellow under the direction Paul Alivisatos at the University of California and Lawrence Berkeley National Laboratory, he studied synthesis and unique ion exchange reactions and resulting novel properties of colloidal nanomaterials. Molecular Engineering and Sciences Seminar Series This weekly seminar brings together students, faculty and invited guests from various disciplines across campus to explore current trends in molecular engineering and nanotechnology. It is a forum for active interdisciplinary discussions. These talks are open to the public and attract a diverse audience of students and faculty. |
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