In the last few years, the exploration of new thermoelectric materials with low-toxicity, earth-abundance, and high-efficiency has become essential. Following this trend, sustainable, easily scalable, and cost-effective fabrication methods, such as electrochemical deposition, are also desirable. In this work, the Pourbaix diagram of silver–selenium–water was developed to find an adequate pH and reduction potential for the electrodeposition of stable silver selenide. Based on this diagram, a solution without the incorporation of additives was developed. Silver selenide films were electrodeposited at different reduction potentials, and after the deposition, the compositional, morphological, and structural characterizations of the silver selenide thin films were analyzed. The thermoelectric properties of the electrodeposited silver selenide films were measured at room temperature. The maximum power factor was found for the films grown at 0.071 V with a value of 3421 ± 705 μW m⁻¹ K⁻² and a thermal conductivity of 0.56 ± 0.06 W m⁻¹ K⁻¹. Even better, when it can be done by employing a technique that is easily scalable to an industrial level and allows large areas to be obtained, such as electrodeposition. Finally, films with similar properties were deposited on a flexible Kapton substrate. A unileg thermoelectric power generator was produced with maximum output powers of 14.7, 29.4, and 37 μW under temperature differences of 10, 15, and 19 K, respectively; and maximum power densities of 55.1, 110.1, and 138.6 mW m⁻² under temperature differences of 10, 15, and 19 K, respectively.