Micro Photovoltaic Modules for Micro Systems

Amorphous silicon based solar modules are very attractive for the powering of various microsystems for both indoor and outdoor applications. This technology offers a lot of flexibility in terms of module design, output voltage, shape, size, choice of substrates and offers also the possibility to embed sensors such as photodiodes. This paper focuses on the development of micro-solar modules with area ≤0.15 cm. Several micro-modules with output voltage of up to 180 V (for a total area of 0.1 cm) were designed and fabricated. The performance limitation introduced by the segment monolithic interconnection and the design of the latter is presented and discussed. An example of a micro-module with a total size of 3.9x3.9 mm developed for a micro-robot with dual voltage outputs and embedded photodiodes is also presented. INTRODUCTION Development of various types of Microsystems (e.g. autonomous micro-systems, sensor networks, micro-robots, etc) requires the parallel development of energy scavenging solutions. Given the energy consumption of most devices, the use of photovoltaic module is a valuable option for many applications [1]. In this context, amorphous silicon (a-Si:H) solar cell technology using micro-fabrication processes offers several advantages. Efficiency values higher than the ones of typical c-Si cells can be obtained due to the more optimal value of the band gap of a-Si:H for most cases of indoor illuminations; for example, an efficiency of 23% can be obtained for a-Si:H in the case of fluorescent light illumination as illustrated in Fig. 1. Voltage and current values can be tailored to the application needs with monolithic interconnections of the module segments, and additional sensors can also be integrated on the same substrate. Furthermore, the solar module can also be designed in any shape in order to maximize the use of the available area. Finally, fabrication on flexible substrate is also possible. Light source Efficiency AM1.5G 10.4% Metal halide HCI 14.8% Halogen 6.1% Fluorescent 23.0%