Flexible multijunction solar cells embedded inside smart dust modules for outdoor applications to Smart Grids

The functioning of self-sustaining smart dust modules plays a vital role in the development of the smart electric grid. In this work, we first devise a flexible triple-junction III-V solar cell embedded inside a smart dust module suitable for outdoor applications. These flexible solar cells are demonstrated to have a bending radius of over 5 cm and exhibit a conversion efficiency of around 25% under air mass 1.5G (1 sun) conditions. Under normal incidence of sunlight at the same conditions, our cell with its small active area of 0.4 cm² can generate around 10.1 mW of electrical power. This is sufficient to meet the direct current power consumption (∼5.4 mW) requirements of our dust module, which includes a temperature/moisture sensor, a 3-axis linear accelerometer, and a Bluetooth chip. In comparison to a silicon-based flexible solar cell, our demonstrated III-V solar cell is smaller, requiring approximately 40% of the area to produce the same electrical power output. Our dust module is controlled using a self-developed Android application installed on a smartphone and can sustain continuous-wave operation for data collection and wireless transmission even when the incident angle of the sunlight reaches 75°. Pulse-mode operation is still possible even in the case of nearly 90° illuminations (for example, at sunset). Overall, the measurement results for this flexible solar cell are promising, allowing for further reduction in the size of a self-sustaining smart dust module with improved reliability. These advantages could facilitate development of the next generation of energy saving smart electric grids.