During the ANTHEM implementation a custom VPI reaction chamber dedicated to thermoelectric material generation and a home-made Seebeck coefficient measurement system were designed, constructed and implemented at the host institute. Using these tools, the gas phase VPI precursors molybdenum(V) chloride (MoCl5) and diethyzinc (DEZ) were screened for sufficient reactivity and stability within the semiconducting polymer matrix of Poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films. The films were infiltrated under different conditions such as cycle number, temperature, exposure time and pulsing time to fine tune the inorganic loading and overall composition. The results indicated that MoCl5 is sufficiently reactive and stable within the P3HT polymer and can lead to improved electrical conductivity, while DEZ showed low reactivity and resulted in little change to the electrical and thermal properties of the polymer.
The electrical conductivity and the Seebeck coefficient of the VPI generated MoCl5/P3HT hybrid materials were analyzed using a probe station and a home-made Seebeck coefficient measurement apparatus, respectively. It was found that the electrical and thermal properties of the hybrid materials could be fine-tuned through the number of VPI cycles. The electrical conductivity reached a maximum of 0.017 S/cm at 175 VPI cycles at 70˚C. Under these conditions the Seebeck coefficient measured 140 µV/K. The films were shown to be stable for over 60 days. The results from these studies were submitted to the AVS 19th International Conference on Atomic Layer Deposition (ALD 2019) under the title “Vapor Phase Infiltration as a New Approach in the Fabrication of Advanced Hybrid Thermoelectric Materials”.
