Solar power for unmanned automonous vehicles
In battlefield environments, the longevity of many electronic sensors such as those found in unmanned aerial vehicles relies on their ability to replenish their energy reserves. Solar radiation is a major potential source of energy and photovoltaic cells offer a promising way to harvest that energy. One possible application is to use the relatively large surface of a microautonomous bat's wings, provided the cells are flexible enough for the wings to flap. In addition, for small platforms with constrained size and weight limitations, it is highly desirable to increase the power density (W/g) substantially from the 0.13W/g that is currently commercially available.
Such cells are currently made using organic cells, amorphous silicon, and pliable arrays of rigid solar cells. Organic solar cells possess benefits in being highly flexible and cheap in production. However, they also have a very short lifetime and low efficiency (~5%). Amorphous silicon is also pliable and inexpensive, but it also suffers from low efficiency as well as low versatility for circuit design. We have developed a new thin-film, pixellated microchip solar-cell-array approach based on quantum dots (QDs) using a dots-in-a-well (DWELL) structure,1 which is pliable, light, and efficient. Our new method of making the array does not result in decreasing efficiency as the flexibility improves. Arrays of these microcells are as efficient as conventional solar panels.
A QD is a semiconductor whose excitons are confined in all three spatial dimensions. As a result, they have properties that are between those of bulk semiconductors and discrete molecules. Figure 1 shows the DWELL structure, where the indium arsenide (InAs) QDs are fully embedded in the gallium InAs quantum wells. Our group has successfully grown DWELL structures since 1999,1 and applied them in various QD devices with state-of-the-art performance, such as low-threshold current-density diode lasers2 and high-responsivity, long-wave IR detectors.
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