Large-area electronics, through the integration of energy-harvesting devices and TFTs, can provide complete powering systems with embedded power electronics on large, flexible sheets. The performance and application range of such systems depends strongly on the characteristics of TFTs and harvesting devices. We explore device constraints and show how novel thin-film circuit topologies, and their optimization (enhanced by large-area passive components), can mitigate these constraints. Two

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... nversion systems serve as vehicles for analysis. I. INTRODUCTION Low-temperature deposition of thin-films can enable the formation of energy harvesting devices on large, flexible substrates. Large physical dimensions enable harvesting of substantial power. The integration of power electronics using the same thin-film technology on a single substrate could form a path for creating complete systems on plastic for addressing a wide range of powering applications. We recently reported two systems that integrate amorphoussilicon (a-Si) solar cells with power inverters built using a-Si thin-film transistors (TFTs) on flexible plastic [1,2], one based on a Class-D power-transfer stage and the other on an LC-oscillator power-transfer stage (harvesting, under indoor conditions, up to 120μW and 22mW respectively). These systems enable near-field wireless power transfer to load devices for applications such as ubiquitous plug-free charging stations [1] and self-powered sensing skins, without requiring external power sources and/or control subsystems (as in [3] ). The two systems represent a range of approaches for power systems illustrating how alternate circuit topologies can address critical TFT limitations, and the ways in which TFT characteristics then set system-level performance (output power and power-transfer efficiency).