Development of flexible thermoelectric device: Improvement of device performance

Thermoelectric (TE) device has some problems, such as low mechanical strength, high manufacturing cost, etc. We are developing flexible TE device using thin films and flexible substrates in order to overcome those problems. The purpose of this work is to fabricate and evaluate the flexible TE device. A flexible TE device consists of vapor-deposited thin films of n- and p-type TE materials between two flexible substrates. The flexible substrate is made up of a combination of polyimide and copper. This structure enables the device itself to convert temperature difference of outer surfaces (DeltaT_out) into in-plane temperature difference (DeltaT _in), and it can generate electricity by the p-n couples. We analyzed temperature distribution of the device by the finite element method (FEM). According to the analysis, a flexible substrate which has thinner polyimide layer (h₁) and thicker copper layer (h₁) is preferable to obtain larger temperature difference. We fabricated flexible TE devices containing 33 pairs of p-n couple, which is composed of chromel and constantan thin films. The device of h ₁/h₂ = 12 mum/70 mum generated 3.72 muW at DeltaT_out = 22.7 K, while 2.40 muW was generated from the device of h₁/h₂ = 35 mum/25 mum at DeltaT _out = 24.0 K. The performance of the flexible TE device was successfully improved as predicted by the analysis