Flexible thermoelectric polymers and systems Thermoelectric materials are important for the sustainable development of human beings because they can be used to directly convert heat into electricity. There is an abundance of low grade heat and exhaust heat on earth but they are usually dissipated to the environment as waste. Thermoelectric materials can be used as the active materials of thermoelectric generators and Peltier coolers. Conventionally inorganic semiconductors or semimetals had shown high thermoelectric performance. However they have problems such as poor mechanical flexibility scarce abundant elements high fabrication cost and toxicity. Great progress has been made on flexible thermoelectric materials including polymers and polymer composites