Flexible Bifunctional Polyimide Film for Daytime Photothermal Power Generation and Nighttime Temperature Control

Abstract

Current solar energy conversion materials based on the photo-thermo-electric effect faced challenges such as intermittent energy conversion, as well as a certain waste of resources and equipment due to unable to work at night. In order to address these issues, we have developed a film for power generation based on the photothermal and thermoelectric effects. In the composite film, the superconducting carbon black connected Bi₂Te_2.7Se_0.3 established an effective conductive pathway in the polyimide (PI), resulting in a Seebeck coefficient (S) of -95 μVK^-1, and a thermoelectric figure of merit (ZT) of 0.18$\times$10^-3 for the composite film. Based on the photothermal and thermoelectric effects, the voltage output of the composite film during the day can be simulated and regulated by adjusting the power parameters of the laser emitter and the position of the laser. The composite film generated an output voltage of 5 mV owing to the exceptional thermoelectric effect. At night, Peltier effect and Joule heating effect permitted the attainment of a maximum temperature of 93 °C and a maximum temperature differential of 10 °C when the load voltage was 2 V. A homemade four-legged thermoelectric system achieved an output voltage of 227 mV and an output power of 2.659 mW at a laser power of 1.5 W/cm². Concurrently, the composite film exhibited optimal mechanical characteristics, and bending cycle stability. As a result, this study provided a novel idea for the multifunctional integration, which not only provided efficient output during the day but also temperature control at night.