Organic thermoelectric (TE) materials are of great interest for researchers in waste heat recovery, especially for waste heat harvesting at near room temperature. Significant progress has been achieved in terms of their figure of merit (zT) values recently, which has presented new insights into the development of organic TE materials. For numerous practical applications of thermoelectric generators, where waste heat is unlimited and cost negligible, the primary goal has been switched to achieve high power output density rather than improving their heat-to-electricity conversion efficiency. In this review, we first discussed the theoretical relationship between the thermoelectric properties of organic materials and the power output density of devices. Then, we analyzed the state-of-the-art strategies for improving the power factor of organic materials. Methods for modulating the structure of the TE legs were discussed with an aim to maintain the temperature difference between the hot side and the cold side of the devices. Finally, some representative devices were summarized for the potential applications of the TEGs along with an outlook on the future of organic thermoelectric materials and devices.