Thermal transport and management in hybrid perovskites have become critical areas of study due to the increasing application of these materials in optoelectronic and photovoltaic devices. Understanding how heat propagates through these materials and how to control it is essential for improving device stability and longevity. Hybrid perovskites exhibit unique thermal properties influenced by their complex crystal structures, organic-inorganic composition, and dynamic lattice behavior. This article focuses on the phonon scattering mechanisms, thermal conductivity measurements, and strategies to mitigate heat-induced degradation in hybrid perovskites.

Hybrid perovskites consist of an inorganic framework interspersed with organic cations, creating a lattice with low thermal conductivity. The primary heat carriers in these materials are phonons, or quantized lattice vibrations. Phonon transport is hindered by several scattering mechanisms intrinsic to hybrid perovskites. One dominant mechanism is anharmonic scattering, arising from the soft and dynamic nature of the perovskite lattice. The large atomic displacements and rotational motions of organic cations introduce strong phonon-phonon interactions, reducing the mean free path of heat-carrying phonons. Another significant mechanism is boundary scattering, particularly in polycrystalline films where grain boundaries act as phonon barriers. The presence of defects, such as vacancies and dislocations, further exacerbates phonon scattering, lowering thermal conductivity.

Thermal conductivity measurements in hybrid perovskites have been conducted using various techniques, including time-domain thermoreflectance (TDTR), frequency-domain thermoreflectance (FDTR), and the 3ω method. Reported values for methylammonium lead iodide (MAPbI3) at room temperature range between 0.3 and 0.6 W/m·K, significantly lower than conventional semiconductors like silicon. The low thermal conductivity is attributed to the combined effects of anharmonicity, organic cation disorder, and nanostructuring. Temperature-dependent studies reveal that thermal conductivity decreases further at higher temperatures due to increased phonon-phonon scattering. In contrast, at cryogenic temperatures, boundary scattering dominates, leading to a plateau in thermal conductivity.

The thermal properties of hybrid perovskites are also influenced by phase transitions. For instance, MAPbI3 undergoes a tetragonal-to-cubic phase transition around 330 K, accompanied by changes in phonon dispersion and scattering rates. The disordered orientation of organic cations in the high-temperature phase introduces additional phonon scattering centers, further suppressing thermal transport. Mixed-halide and mixed-cation perovskites exhibit even more complex behavior due to compositional heterogeneity, which can either enhance or reduce thermal conductivity depending on the local lattice strain and defect distribution.

Heat-induced degradation is a major challenge for hybrid perovskite devices, particularly under operational conditions where localized heating can accelerate decomposition. Thermal degradation pathways include the volatilization of organic components, phase segregation in mixed-halide systems, and irreversible lattice collapse. To mitigate these effects, several strategies have been explored. One approach involves compositional engineering, where thermally stable cations such as formamidinium (FA) or cesium (Cs) are incorporated to suppress organic loss. Mixed-cation perovskites like FAxMA1-xPbI3 demonstrate improved thermal resilience compared to pure MAPbI3.

Another strategy focuses on interfacial thermal management. Incorporating thermally conductive additives or scaffolds, such as graphene or boron nitride, can enhance heat dissipation from active perovskite layers. These materials provide alternative phonon pathways, reducing hot-spot formation. Encapsulation with thermally stable polymers or inorganic layers also helps by preventing moisture ingress and mechanical degradation under thermal cycling. Additionally, nanostructuring the perovskite layer to form ordered grain boundaries or superlattices can optimize phonon transport while maintaining structural integrity.

Recent advances in computational modeling have provided deeper insights into thermal transport mechanisms in hybrid perovskites. Molecular dynamics simulations and first-principles calculations reveal the role of organic cation dynamics in phonon scattering and predict how chemical modifications can alter thermal conductivity. Machine learning approaches are also being employed to identify optimal compositions and architectures for thermal management.

In summary, thermal transport in hybrid perovskites is governed by strong phonon scattering mechanisms arising from lattice anharmonicity, organic cation disorder, and microstructural defects. Experimental measurements confirm their low thermal conductivity, which poses challenges for heat dissipation in devices. However, through compositional tuning, interfacial engineering, and advanced encapsulation, it is possible to enhance thermal stability and mitigate degradation. Future research should focus on developing scalable thermal management solutions that do not compromise the optoelectronic performance of these materials. Understanding and controlling thermal properties will be crucial for the long-term reliability of hybrid perovskite-based technologies.