Multi-physics mechanisms and regulation of perovskite grain boundaries: insights into carrier dynamics, ion migration, thermodynamics, and thermal stress

Abstract

Grain boundaries (GBs), inherent in polycrystalline perovskite films and associated with numerous trap states, are widely regarded as non-radiative recombination centres that degrade the performance of perovskite solar cells (PSCs). Current research on GBs is limited to carrier dynamics, which, however, lacks a comprehensive multi-physics perspective encompassing thermal generation/transport/dissipation and internal-stress formation/accumulation in GB-containing PSCs. Herein, we systematically elucidate the multi-physics mechanisms of GBs by integrating carrier-transport, ion-migration, thermodynamics, and thermal-stress analyses through opto-electro-thermal-stress coupled simulations and well-designed experiments. Notably, electrical simulation results reveal that the reason why GBs generally degrade device performance can be attributed to their beneficial role in carrier transport being surpassed by carrier recombination losses. Additionally, GB-containing PSCs exhibit distinct ion dynamic behaviour, with ions accumulating preferentially at GBs or within perovskite grains, further compromising PSC efficiency and stability. More importantly, we demonstrate that filling or passivating GBs and surface GB grooves with wide-bandgap materials effectively mitigates performance degradation. Thermal-stress simulations further show that GB-containing PSCs generate more heat than their GB-free counterparts, leading to elevated device operating temperatures, localized thermal-stress accumulation at GBs, and accelerated performance degradation. Experimental results confirm that passivating GBs with suitable materials simultaneously alleviates thermal conductivity inhomogeneity and thermal-stress accumulation, offering new insights into the multi-physics mechanisms of GB-containing PSCs.