Avoiding errors in efficiency measurements of high-performance thermoelectric generator modules: Toward best practices for materials researchers

The recent surge in reports on high-efficiency thermoelectric generator modules brings two conflicting feelings: excitement and confusion. The confusion comes from the fact that there is no widely accepted standard protocol for efficiency measurement. The standardised protocol should be easy to follow for materials researchers, who fabricate and measure generator modules using emerging thermoelectric materials of their own. Here, as a balanced method in terms of reliability and simplicity, we demonstrate straightforward measurement setup and procedure. To compare thermoelectric generator modules with various materials, size, and measurement conditions, we propose to explicitly distinguish intrinsic contributions to the efficiency from extrinsic effects such as surface radiation loss. We confirm that too quick measurements before attaining thermal stabilization can cause serious overestimation of the conversion efficiency by up to 27%. To reliably evaluate the maximum efficiency and output power, we adopt a nonlinear current sweep to directly measure the output power and heat flow in a short timeframe. We believe that this work will promote discussion among the community to achieve consensus on the efficiency measurements of thermoelectric modules, which will enable detailed comparative analyses of the results reported by various research groups.