Quantum dot-based intermediate band solar cells
Harley T. Johnson
Department of Mechanical Science and Engineering
University of Illinois at Urbana-Champaign
Room 341-A
Friday, December 10 2010 at 1:30 PM
Resource Center for Science and Engineering
Rio Piedras Campus
University of Puerto Rico
Abstract:
Nanostructured materials will contribute significantly to potential advances in next generation photovoltaics. To compete with conventional silicon and thin film solar cell designs, new technologies must deliver much higher efficiencies, through development of new heterostructures for improved energy conversion, or other niche advantages, such as flexible or ultrathin form factors. Intermediate band solar cells (IBSC) are one proposed heterostructure solution with the potential for high energy conversion efficiency. Here, we examine the influence of strained, self-assembled quantum dot (QD) superlattices on photoabsorption in p-i-n heterostructures as a possible IBSC implementation. Realistic QD shapes and sizes from cross-sectional scanning tunneling microscopy and areal densities from atomic force microscopy are used in a finite-element Schrödinger-Poisson model in order to predict the external quantum efficiency (EQE) of the QD solar cell. Experimental and computed EQEs suggest that the additional long-wavelength absorption is due to transitions between miniband states induced by the distribution of QDs, with minimal contributions from diffuse wetting layers. Variations in QD sizes and shapes among heterostructure layers strongly affect the sub-bangdap EQE spectrum of the device. Based on these results, it is possible to develop relatively simple design rules for increasing photoabsoption into the QD minibands, but several key challenges remain in using this architecture for the design of highly efficient solar cells. As such, the mechanics and materials issues for this potential IBSC design are discussed in the context of other promising photovoltaic technologies.
Biosketch:
Harley T. Johnson is an Associate Professor and Cannon Faculty Scholar in the Department of Mechanical Science & Engineering, and a member of the Frederick Seitz Materials Research Lab and the Beckman Institute for Advanced Science and Technology at the University of Illinois at Urbana-Champaign. Prof. Johnson’s research group studies the mechanics of electronic and optical materials, focusing on the effects of deformation, defects, and disorder on functional properties of materials and devices. Prof. Johnson has been at Illinois since 2001, following two years as an Assistant Professor at Boston University. He earned the Ph.D. degree in Engineering from Brown University in 1999, Masters Degrees from Brown in Applied Mathematics (1998) and Engineering (1996), and a Bachelor’s in Engineering Science & Mechanics, with highest honors, from Georgia Tech in 1994. Prof. Johnson received the NSF CAREER Award in 2001, was named Cannon Faculty Scholar in 2003, and has been recognized numerous times for outstanding teaching. He has been selected to receive the 2010 ASME Thomas J. R. Hughes Young Investigator Award for Special Achievement in Applied Mechanics.
