Modeling the heat conductivity across bulk grain and grain boundaries in perovskite solar cells

This study explores the heat conductivity across the grains and grain boundaries in polycrystalline perovskite thin films, where heat transfer is primarily mediated by phonons. Grain boundaries significantly influence the heat conduction process, as scattering at these boundaries reduces the thermal conductivity and introduces anisotropy. Using a phenomenological model, it is shown that increased grain boundaries in the absorber layer of perovskite solar cells amplify anisotropy and resistance to heat conduction, particularly at elevated temperatures. Optimal grain dimensions (50 nm thickness, 135 nm width) were obtained and shown to enhance the effective heat conductivity (κeff), which surpasses heat conductivity at grain boundary (κGB) at higher temperatures. Additionally, defect density and carrier lifetime affect thermal properties, especially at grain boundaries which could hinder the heat mitigation at longer carrier lifetime. A modeling approach using a limited number of parameters has been developed and interlinked to show how the heat generated in the absorber layer faces resistances at bulk and grain boundaries of perovskite layer. Also, the equivalent circuit of the cells with thick or thin grains were designed for a better understanding of heat resistance across grains and grain boundaries.