The effective utilisation of thermal energy is crucial to a world aiming at sustainable development goals. The sensitised thermal cell (STC) is a new thermal energy conversion technology, which was reported in 2017, for generating electricity via the redox reactions of electrolyte ions with thermally excited carriers in semiconductors. STC is attracting attention as a technology that could affect oil prices globally. Here, we report the successful construction of STC, which discharges and recovers well at room temperature, by studying the interelectrode and ion diffusion distances. The fabricated STC is thinner than 0.5 mm and can be rendered flexible. Further, STCs, which possess a power generation capacity of 0.1 microA, 100 mV per 1 mm2 area, and shall be installed “in” internet-of-things (IoT) devices, drainage pipes, and walls in the future.