Almost all traditional energy sources are on the point of rapid depletion due to over use. There is demand for alternative renewable energy sources, and thermoelectric generators (TEGs) are one of the rising solutions. TEGs are a new class of solid-state devices that transform waste heat energy directly into electricity using Seebeck effect. The efficiency of TEGs is governed by dimensionless quantity called Figure of merit (ZT), which plays an important role to determine the overall sustainability of TEGs. Traditional thermoelectric generators have a poor efficiency (12-20%), which is a disadvantage. To obtain higher value of ZT, the prime emphasis is given towards material engineering as the efficiency solely depends on the materials selection. The investigation is on earth-abundant, cost-effective, low-toxic innovative nanomaterials. In addition, the paper covers various elements for TEGs with prime focus towards rare earth free materials and their emerging trends.