Thermoelectrics has a potential to recover usable energy from waste heat and capture handy energy from the environment. The largest amount of heat are wasted in the low temperature region ~ 150°C , because the conventional systems lost the recovery power for such low temperature heat. Thermoelectrics, however, can maintain the energy convergent efficiency to exceed the conventional systems in the efficiency for the low temperature region . Differing from inorganic thermoelectric materials, organic thermoelectric materials can provide a further value: flexibility. The thermoelectric figure of merit has also been dramatically improved to 0.42, recently . The Seebeck effect, however, generates only several ten µV/K. To drive electric devices, we need to pattern and connect more than one hundred thermoelectric cells as a thermoelectric module.
Herein, we utilized photolithography to fabricate organic π-type thermoelectric modules. We can simply fabricate one-leg thermoelectric modules via printing the bottom electrodes, organic thermoelectric materials, and the upper electrodes which electrically connect with the next bottom electrodes. However, the organic one-leg thermoelectric modules cannot generate electricity because the upper electrodes connecting with the next bottom electrodes conduct the heat and kill the temperature difference for the thermoelectric generation. To maintain the temperature difference by separating the upper and bottom electrodes, we fabricated π-type thermoelectric modules via fulfilling p-type and n-type thermoelectric materials into photolithographically patterned resist molds. Overall, we re-arrange the well-established fabrication processes, such as photolithography, fulfilling, and electrode deposition, to emergently fabricate the organic π-type thermoelectric modules.
To achieve 250 mV to drive a booster circuit, we designed a module pattern, 13 × 13 cells in 40 × 40 mm2. We fulfilled p-type and n-type thermoelectric materials based on poly(3,4-ethylenedioxy thiophene) polystyrene sulfonate  and tetrathiafulvalene 7,7,8,8-tetracyanoquinodimethane salt , respectively. When the single π unit reaches 3 mV, the designed module can drive electric devices with a booster circuit. In the presentation, we report the details of the optimized thermoelectric materials and the module performances.
1. Shindo, T., Nakatani, Y., Oishi, T. Toshiba Review (in Japanese) 63, 7–10 (2008).
2. Vining C. B., Nat. Mater. 8, 83–85 (2009)
3. Kim, G-H., Shao, L., Zhang, K., Pipe, K. P. Nat. Mater. 12, 719–723 (2013)
4. Bubnova, O., Khan Z. U., Malti, A., Braun, S., Fahlman, M., Berggren, M., Crispin, X. Nat. Mater. 10, 429–433 (2011)