Single-nanowire, low-bandgap hot carrier solar cells with tunable open-circuit voltage
Steven Limpert, Adam Burke, I-Ju Chen, Nicklas Anttu, Sebastian Lehmann, Sofia Fahlvik, Stephen Bremner, Gavin Conibeer, Claes Thelander, Mats-Erik Pistol, Heiner Linke
Compared to traditional pn-junction photovoltaics, hot carrier solar cells offer potentially higher efficiency by extracting work from the kinetic energy of photogenerated "hot carriers" before they cool to the lattice temperature. Hot carrier solar cells have been demonstrated in high-bandgap ferroelectric insulators and GaAs/AlGaAs heterostructures, but so far not in low-bandgap materials, where the potential efficiency gain is highest. Recently, a high open-circuit voltage was demonstrated in an illuminated wurtzite InAs nanowire with a low bandgap of 0.39 eV, and was interpreted in terms of a photothermoelectric effect. Here, we point out that this device is a hot carrier solar cell and discuss its performance in those terms. In the demonstrated devices, InP heterostructures are used as energy filters in order to thermoelectrically harvest the energy of hot electrons photogenerated in InAs absorber segments. The obtained photovoltage depends on the heterostructure design of the energy filter and is therefore tunable. By using a high-resistance, thermionic barrier an open-circuit voltage is obtained that is in excess of the Shockley-Queisser limit. These results provide generalizable insight into how to realize high voltage hot carrier solar cells in low-bandgap materials, and therefore are a step towards the demonstration of higher efficiency hot carrier solar cells.
Combining metal dewetting and lateral etching for the scalable top-down fabrication of GaN nanowire arrays with independently tunable diameter and spacing
在声子学领域，周期性模式控制振动，从而控制物质中的热和声音的流动。在这种声子晶体中产生的带隙实现了低耗散振动模式，并实现了对机械量子比特、高效波导和最先进传感的应用。在这里，我们结合声子和二维材料，并探讨通过施加机械压力操纵声子晶体的可能性。为此，我们制造了最薄的声子晶体从单层石墨烯和模拟其振动特性。我们发现一个带隙的MHz制度，在此范围内，我们本地化的缺陷模式与一个小的有效质量为0.72 ag = 0.002 $m_{physical}$。最后，我们利用石墨烯的灵活性和机械调谐有限大小的声子晶体。在高达30千帕的静电压力下，我们观察到整个声子系统的频率上升超过350%。同时，缺陷模式保持在带隙内并保持局部化，这表明高质量、动态可调的机械系统。
