InP Nanowire Array Solar Cells Achieving 13.8% Efficiency by Exceeding the Ray Optics Limit.
ABSTRACT Photovoltaics based on nanowire arrays could reduce cost and materials consumption compared to planar devices, but have exhibited low efficiency of light absorption and carrier collection. We fabricated a variety of millimeter-sized arrays of p-i-n doped InP nanowires and found that the nanowire diameter and the length of the top n-segment were critical for cell performance. Efficiencies up to 13.8% (comparable to the record planar InP cell) were achieved using resonant light trapping in 180-nanometer-diameter nanowires that only covered 12% of the surface. The share of sunlight converted into photocurrent (71%) was six times the limit in a simple ray optics description. Furthermore, the highest open circuit voltage of 0.906 volt exceeds that of its planar counterpart, despite about 30 times higher surface-to-volume ratio of the nanowire cell.
SourceAvailable from: Anna Fontcuberta i Morral[Show abstract] [Hide abstract]
ABSTRACT: Nanowire diameter has a dramatic effect on the absorption cross-section in the optical domain. The maximum absorption is reached for ideal nanowire morphology within a solar cell device. As a consequence, understanding how to tailor the nanowire diameter and density is extremely important for high-efficient nanowire-based solar cells. In this work, we investigate mastering the diameter and density of self-catalyzed GaAs nanowires on Si(111) substrates by growth conditions using the self-assembly of Ga droplets. We introduce a new paradigm of the characteristic nucleation time controlled by group III flux and temperature that determine diameter and length distributions of GaAs nanowires. This insight into the growth mechanism is then used to grow nanowire forests with a completely tailored diameter-density distribution. We also show how the reflectivity of nanowire arrays can be minimized in this way. In general, this work opens new possibilities for the cost-effective and controlled fabrication of the ensembles of self-catalyzed III-V nanowires for different applications, in particular in next-generation photovoltaic devices.Nanotechnology 02/2015; 26(10):105603. DOI:10.1088/0957-4484/26/10/105603 · 3.67 Impact Factor
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ABSTRACT: We have investigated the p-type doping profiling of InAs nanowries (NWs) grown via the Au-assisted vapor-liquid-sold (VLS) and the self-assembled growth methods. The VLS is the most commonly used mechanism for the growth of semiconductor NWs. The VLS-grown InAs NWs, however, show a large degree of variation in their electrical resistance along their growth direction. In addition, attempts to form heavily p-type doped InAs NWs lead to a strong kinking in the shapes of the NWs, disturbing their one-dimensional growth. In contrast, the p-type doped InAs NWs grown via the self-assembled method exhibit very low and uniform electrical resistance along the growth direction of the NWs. The doping mechanisms of the InAs NWs and their growth methods are further discussed.Journal- Korean Physical Society 06/2014; 64(11):1621-1625. DOI:10.3938/jkps.64.1621 · 0.43 Impact Factor
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ABSTRACT: Live observations of growing nanowires using in situ transmission electron microscopy (TEM) is becoming an increasingly important tool for understanding the dynamic processes occurring during nanowire growth. Here we present observations of growing InAs nanowires, which constitute the first reported in situ growth of a In-V compound in a transmission electron microscope. Real time observations of events taking place over longer growth lengths were possible due to the high growth rates of up to 1 nm/s that were achieved. Straight growth (mainly in aOE (c) 111 > B directions) was observed at uniform temperature and partial pressure while intentional fluctuations in these conditions caused the nanowires to form kinks and change growth direction. The mechanisms behind the kinking are discussed in detail. In situ observations of nanowire kinking has previously only been reported for nonpolar diamond structure type materials (such as Si), but here we present results for a polar zinc blende structure (InAs). In this study a closed cell with electron and X-ray transparent a-SiN windows was used in a conventional high resolution transmission electron microscope, enabling high resolution imaging and compositional analysis in between the growth periods.Nano Research 08/2014; 7(8):1188-1194. DOI:10.1007/s12274-014-0481-4 · 6.96 Impact Factor