Chemical bond engineering toward extraordinary power factor and service stability in thermoelectric copper selenide

Porous structures can hinder phonon transport but inevitably deteriorate electrical and mechanical properties. In order to suppress the formation of pores, we propose a chemical bond engineering strategy to constrain the volatile Se in Cu₂Se-based materials via applicable elemental substitution. Benefiting from the reduced porosity and successful dual doping, Cu vacancies and carrier mobility are optimized for the Gd₂S₃-added Cu_1.99Se samples, leading to an ultrahigh power factor of ∼17.4 μW cm⁻¹ K⁻² at 1,000 K and a high figure of merit of ∼2.5 at 1,050 K. The fabricated segmented single-leg device maintains a high conversion efficiency of ∼9.0% and a power density of ∼636.3 mW cm⁻² at ΔT = 516 K without obvious degradation over 110 cycles of stability tests. Our work demonstrates a paradigm to control the porosity caused by elemental volatilization, providing more opportunities to enhance both the thermoelectric performance and service stability.