Grants and Contributions:

Grant or Award spanning more than one fiscal year. (2017-2018 to 2022-2023)

In the past 3 years, Fafard’s team made breakthrough optoelectronic device advancements, now featuring the highest optical to electrical conversion efficiency ever for any type of devices. The progress has been presented recently at several invited international presentations and late-news scientific papers. This recent development in the area of advanced III-V heterostructures allowed attaining greater than 65% optical to electrical conversion efficiencies. The current proposal is to further advance the understanding and the development with these novel III-V semiconductor phototransducers. The record-efficiency devices are based on a novel vertical epitaxial heterostructure architecture (VEHSA) design. Thanks to a precise control of thin semiconductor layers grown by Metal-Organic Chemical Vapor Deposition epitaxy or by chemical beam epitaxy, the unprecedented performance can be obtained with tailored output voltages adapted for various applications. The proposed research is therefore in the area of nanoscale p/n junctions and will reveal very interesting properties for photovoltaic devices engineered with ultra-thin bases, including photon recycling effects. The heterostructure designs yielded high external quantum efficiency (EQE) values for all the structures studied experimentally, up to 20 ultra-thin subcells (PT20 devices) to date. Conversion efficiencies greater than 60% were confirmed for all structures, including recently the PT20s. Additionally, these high efficiencies can be maintained for high electrical output powers, reaching greater than 3W for chips only a few mm 2 in area. Record high-photovoltage values for monolithic photovoltaic cells with V oc > 23V have been obtained with the PT20 studied. The PT20 structure has been implemented with its narrowest ultrathin base having a remarkable thickness of only 24nm, but for future developments, the device modeling shows that the high-photovoltage and the unprecedented conversion efficiency values are expected to be achievable for a much higher number of ultrathin junctions, getting into the range where 2-dimensional quantum well effects are becoming significant. For example, we derived that the narrowest subcell of a PT60 structure would have a base as thin as 8nm, it is expected to still generate a photovoltage of 1.14V per individual subcell, and it will begin to feature 2-dimensional quantum well effects. The proposal will enable key progress in this area while leveraging the achievements accomplished in the very fruitful initial phase of the research. The thermalization losses will be minimized to reach higher efficiencies and the open circuit voltage will be further increased by adding more n/p junctions to the VEHSA design. The devices will be built into systems that will benefit from the unique device properties. Also the VEHSA design will be implemented to other alloys, enabling longer wavelengths.