UNS: Performance Optimized Intermediate Band Photovoltaic Devices based on Type-II Quantum Dots

Cuny Queens College, Flushing NY

Investigators

Abstract

PI: Igor L Kuskovsky Proposal Number: 1512017 The sun represents the most abundant potential source of sustainable energy on earth. Solar cells made from thin films of nanometer-sized crystals called quantum dots are potentially less expensive and more efficient than crystalline silicon solar cells currently in commercial use. The goal of this project is to engineer the composition and size of the quantum dots to enhance the collection of solar energy in the ultraviolet and infrared wavelengths of the solar spectrum, resulting in potentially high solar energy conversion efficiency and power output. The quantum dots will be made from mixtures of the elements zinc, selenium, cadmium, and tellurium as model compounds for scientific study. The composition of these mixtures will be guided by computer simulations. The proposed research may lead to the discovery of new quantum mechanical processes for solar energy conversion. As part of the educational activities associated with the project, the principal investigator will mentor high school students through Queens College Summer Science Program on nanotechnology related projects for science fair competitions in the state of New York. The overall goal of the proposed research is to develop Type-II quantum-dot photovoltaic (PV) semiconductor materials that enable the absorption of light below the band gap of the host material, leading to higher solar energy conversion efficiency. Toward this end, Type-II quantum dots will be imbedded into a wide band-gap semiconductor host to make an intermediate band gap material with photon absorption characteristics mapped to the solar spectrum in the ultraviolet to infrared range, using material systems and synthesis approaches that lead to increase of photocurrent without loss of open circuit voltage. Toward this end, the research plan will integrate material synthesis, band gap calculations, and PV device simulation to identify ideal intermediate band gap PV materials. The candidate material systems consist of a p-ZnSeTe/Zn(Cd)Te-ZnCdSe/n-ZnCdSe structure with embedded Zn(Cd)Te-ZnCdSe type-II quantum dots. The barriers, latticed matched to the InP substrate, have the bandgaps of about 2.1 eV, while the quantum dots have a valence band offset of 0.8-1.0 eV. These parameters will be achieved by controlling quantum dot size and chemical composition. To accomplish effective partial filling of the intermediate band, a structure with alternatively doped quantum dot layers will be engineered. Film growth will be designed to avoid formation of a wetting layer that can lower the open circuit voltage of the final material. This process will also allow for the deposition of several hundred defect-free quantum dot layers for improved light absorption. Device-level simulation will characterize the interplay between device configuration and recombination processes associated with these intermediate band gap materials. Based on the research, instructional material will be developed on the topic of fabrication of Type-II quantum dots for solar cell applications, and will be used in courses for a professional Master's degree program in Photonics at Queens College, The City College of New York.