Record Efficiency Photovoltaic Heterostructures

在过去的3年里，Fafard的团队在光电器件方面取得了突破性的进展，目前在任何类型的器件中都具有最高的光到电转换效率。最近在几次受邀的国际演讲和最新的科学论文中介绍了这一进展。最近在先进III-V异质结构领域的发展使得实现大于65%的光电转换效率。目前的建议是进一步推进对这些新型III-V半导体光换能器的理解和发展。记录效率器件基于一种新颖的垂直外延异质结构（VEHSA）设计。由于通过金属有机化学气相沉积外延或化学束外延生长的薄半导体层的精确控制，可以通过适合各种应用的定制输出电压获得前所未有的性能。因此，提出的研究是在纳米级p/n结领域，并将揭示超薄基底光伏器件的非常有趣的特性，包括光子回收效应。异质结构设计为实验研究的所有结构提供了高外量子效率（EQE）值，迄今为止多达20个超薄亚电池（PT20器件）。所有结构的转换效率都超过60%，包括最近的pt20。此外，这些高效率可以保持高电输出功率，达到大于3W的芯片只有几平方毫米的面积。通过PT20的研究，获得了Voc > 23V的单片光伏电池的高光电压值。PT20结构已经实现了其最窄的超薄基底厚度仅为24nm，但对于未来的发展，器件建模表明，高光电电压和前所未有的转换效率值有望实现更多数量的超薄结，进入二维量子阱效应变得重要的范围。例如，我们推导出PT60结构的最窄亚电池的基底薄至8nm，预计每个亚电池仍能产生1.14V的光电压，并且它将开始具有二维量子阱效应。该提案将使这一领域取得关键进展，同时利用在非常富有成效的研究初始阶段所取得的成就。通过在VEHSA设计中增加更多的n/p结，可以将热化损耗降至最低以达到更高的效率，并进一步提高开路电压。这些设备将被内置到将受益于独特设备属性的系统中。此外，VEHSA设计将应用于其他合金，实现更长的波长。

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 mm2 in area. Record high-photovoltage values for monolithic photovoltaic cells with Voc > 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.