Introduction

The rapid global expansion of artificial intelligence (AI) and the Internet of Things (IoT) is driving a continuous surge in energy consumption and associated carbon dioxide emissions. Addressing this challenge requires moving beyond improvements in centralized power generation to develop sustainable, device-level energy supply solutions. Modern society produces vast amounts of untapped, low-temperature waste heat, with ubiquitous temperature gradients present in buildings, industrial equipment, outdoor infrastructure, and even the human body. This chapter introduces organic thermoelectric devices and thermocells as highly effective technologies for converting this ambient heat into electrical energy. By combining solid-state and liquid-state systems, thermal energy can be efficiently recovered across a wide temperature range—from room temperature up to approximately 200°C.