Implementation of 3ω Method for Studying the Thermal Conductivity of Perovskite Thin Films

In this paper, an approach for precise determination of the thermal conductivity of novel lead-free perovskite thin films by 3ω method, realized with a field programmable analog array circuit, is presented. The objective of the work is to study the relation between the thermal conductivity of the photoelectric perovskites and the thermal stability of the solar cells, in which they are incorporated. It is found that the solar cells’ long-term stability under different exploitation conditions, such as continuous illumination and elevated temperatures, is affected to a different extent, according to the thermal conductivity. The developed setup for implementation of the 3ω method is adapted for thin-film samples and can be applied to all layers involved in the solar cell, thus defining their individual contribution to the overall device thermal degradation. According to the conducted measurements, the coefficients of thermal conductivity for the novel materials are as follows: for the iodine-based perovskite film, it is 0.14 W/mK and for the chlorine-based perovskite film, it is 0.084 W/mK. As a result, the thermal instability and degradation rate at continuous illumination are, respectively, 10.6% and 200 nV/min for the iodine-based perovskite solar cell, and 6.5% and 20 nV/min for the chlorine-based cell. At elevated temperatures up to 54 °C, the corresponding instability values are 15 µV/°C with a degradation rate of an average of 2.2 µV/min for the cell with iodine-containing perovskite and 300 nV/°C with a degradation rate of 66 nV/min for the cell with chlorine-containing perovskite.