Plenary speakers: Nanotechnology enabled pathways for energy conversion

Abstract

Nanostructured solar cells have multiple approaches by which they can improve photovoltaic performance through new physical approaches in order to reach thermodynamic limits of energy conversion, circumventing material limitations through bandgap engineered systems and providing new routes for low-cost fabrication by self-assembly or design of new materials. In the present talk, we focus on pathways to high efficiency solar cells and energy conversion using various approaches employing nanostructured materials. We first discuss the limits of conventional photovoltaics, and advanced concept approaches to exceed the so-called Shockley-Queisser limit for single bandgap cells. We then discuss particular approaches that are actively being investigated including Si heterojunction solar cells with carrier selective contacts, nanowire solar cells as active components of multi-junction solar cell, quantum dot solar cells for intermediate band devices, and multiexciton generation for increasing the quantum yield above unity in quantum dot and nanowire structures. Hot carrier solar cells are another approach to high efficiency discussed, where the critical issue is reducing the energy loss rate of photoexcited carriers, either in low-dimensional nanostructured materials where this rate is reduced, or in phononic bandgap materials in which nonequilibrium phonons reduce carrier cooling, and allow extraction at high energy. Another way that nanomaterials improve efficiency which we discuss, is in improving light trapping of incident solar radiation, using nanowires and nanoparticles as scatterers in the diffraction limit, to increase absorption by increasing the optical path length in the device. Finally, we discuss hybrid high temperature multijunction photovoltaics coupled with concentrating solar thermal in order to improve the system efficiency above either that of the photovoltaic or CSP system by itself.