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Introduction
The rapid progress in flexible electronics has catalyzed an exigent need for power sources adaptable to the inherent flexibility of these systems1. Flexible thermoelectric films, capable of conforming to the skin and continuously converting temperature difference between the human body and the ambient environment into electrical energy for flexible electronics, are viewed as a highly promising flexible self-powered energy source2,3. Optimizing the power factor (PF) of the flexible thermoelectric film is the key to improving its output power density to meet the energy supply needs of as many electronic products as possible4.
Due to its better mechanical properties and lower toxicity compared to the traditional BiTeSe alloys, N-type silver selenide (β-Ag2Se at room temperature) has attracted sharply increasing attention in the field of flexible thermoelectric films5,6. However, although its Hall carrier mobility (μH) reaching up to 2000 cm2V−1s−1 at room temperature, the values of density-of-states effective mass (md) for carriers in the stoichiometric β-Ag2Se are far smaller than that of BiTeSe alloys7, 8–9. Furthermore, owing to the doping limits of most elements (including Ag and Se) in β-Ag2Se being less than 0.1 mole%, the intrinsic small carrier concentration (nH) of stoichiometric β-Ag2Se can hardly be effectively elevated through doping or altering the Ag/Se ratio since the 1960s10, 11, 12–13. Thus, the state-of-art values of PF for stoichiometric β-Ag2Se, in both bulk and film forms, typically remain below 2700 μWm−1K−2 or even 2000 μWm−1K−2 at around room temperature for decades, which is markedly inferior to the exceeding 4000 μWm−1K−2 obtained by BiTeSe alloys4,14, 15–16. On the other hand, despite incorporating metals or alloys as the second phase has been proven to enable the promotion of nH and enhancement of md in β-Ag2Se-based flexible films17,18, the values of PF for these films are still limited by the excessively high nH and additional carrier scattering at phase boundaries19, 20, 21–22.
Very recently, we revealed that a previously...