Flexible pCu2Se-nAg2Se thermoelectric devices via in situ conversion from printed Cu patterns.

• Flexible thermoelectric devices are in situ fabricated from printed Cu patterns. • Rationally designed nanosheets arrays result in strong phonons scattering. • Optimal ZT values of 0.5 for Cu 2 Se and 0.7 for Ag 2 Se were achieved. • The device exhibits outstanding power density of 13.4 W m−2 (△T = 40 K) Flexible thermoelectric (TE) devices have great potential in wearable electronics, but there is great challenge to realize robust TE device with high performance via feasible integration process. Herein, based on precisely printed copper patterns, a flexible p Cu 2 Se- n Ag 2 Se TE device is initially realized by in situ ion exchange reaction. The as-prepared Cu 2 Se and Ag 2 Se films possess typical hierarchical defects including atomic scale vacancies, the nanosheet fragments and microscale porous structure, which could significantly scatter phonons in wide frequency range. Accordingly, ultra-low thermal conductivity (Cu 2 Se: 0.13 W m−1 K−1; Ag 2 Se: 0.15 W m−1 K−1) and optimal ZTs (Cu 2 Se: 0.5; Ag 2 Se: 0.7) are achieved. Meanwhile, the as-fabricated p Cu 2 Se- n Ag 2 Se TE device exhibits an excellent power density of 13.4 W m−2 at a temperature gradient of 40 K, which is among the highest values of printed in-plane film devices. Furthermore, the good adhesion between TE films and porous PI substrate endowed excellent flexibility and stability of p Cu 2 Se- n Ag 2 Se devices. [ABSTRACT FROM AUTHOR]