THERMOELECTRIC ENERGY HARVESTING IN DISPLAYS

Abstract

The development of a complete thermoelectric generator and its application on a display polarizer film was successfully accomplished in this thesis. A systematic study of the prospective thermoelectric materials, PEDOT:PSS-based and ${ZnON}$, used for the present application is presented. To the best of our knowledge, this is the first exploration of the thermoelectric parameters of ${ZnON}$ reported here. Thin-film deposition of these materials was performed via both solution- and vacuum-based techniques. In addition, certain doping mechanisms were tested in an attempt to further understand the correlation between electrical conductivity and Seebeck coefficient. A maximum power factor of $42{\mu}Wm^{-1}K^{-2}$ was achieved for the PEDOT:PSS-based thin film at room temperature. It was initially doped via 5vol% of DMSO and sequentially treated with ethylene glycol. Specifically, its electrical conductivity displayed a 2-fold increase after EG treatment, reaching a value of about 1632 Scm$^{-1}$. Systematic studies performed on the association between thin-film thickness and its Seebeck coefficient shows a decrease in the latter as the number of multilayers printed increases. Among the different $O_{2}/N_{2}$ ratios that were tested for ${ZnON}$ thin films, a maximum power factor value of 163${\mu}Wm^{-1}K{-2}$ was achieved with the lowest $O_{2}$ flow rate configuration. In contrast to PEDOT:PSS-based thin films, the ${ZnON}$ displayed the opposite effect on the relation of the Seebeck coefficient with respect to thin-film thickness. Furthermore, a heterostructure was also developed by implementing ${ZnO}$ nanowires into the ${ZnON}$ thin film. ${ZnO}$ nanowires have been fabricated through the hydrothermal method on inkjet-printed patterns of zinc acetate dihydrate. It has been demonstrated that with the right inkjet-printing parameters and substrate temperature, ${ZnO}$ nanowires can be effortlessly fabricated in accordance with the desired pattern variations under low temperature and mild conditions. Finally, a complete device of the thermoelectric generator was fabricated using the above materials and a special set-up developed in order to test the device on the polarizer. The power output achieved from a 1-thermoelectric couple under normal backlight illumination and ambient conditions was 23pW. Overall, it is thought that the particular design and proof of concept presented here can be the basis of a prospective energy harvesting scheme via thermoelectrics in future display-based handheld devices.