Motivation: A central question in perovskite solar cell (PSC) stability research is whether bias-sweep instability can be explained solely by ion migration, or whether additional intrinsic mechanisms contribute under realistic operating conditions. We demonstrate that the coupled interplay between ion migration, self-heating, and the internal electric field in PSCs opens a distinct non-isothermal instability signature, which we term thermal hysteresis [1]. Relaxing the quasi-isothermal assumption commonly adopted in mixed electronic-ionic transport models can change not only the magnitude of hysteresis, but also its mechanistic origin and timescale.

Methodology: We develop a self-consistent optical-electrical-ionic-thermal multiphysics framework that resolves layer- and interface-resolved heat-generation mechanisms across the full device stack [1]. We track spatiotemporal hotspot footprints during bias sweeps, capturing where dissipation localizes and how ionic screening redistributes it. Moving beyond conventional J–V analysis, we introduce temperature–voltage (T–V) and heat–voltage (P–V) diagnostics that capture scan-rate-dependent thermal hysteresis and identify its dominant physical contributors.

Results: PSCs develop internal thermal inertia on timescales comparable to ionic relaxation during bias sweeps. At intermediate scan rates, coupled thermo-electro-ionic interactions produce non-monotonic temperature evolution, characterized by dual-peak forward-scan profiles and pronounced T–V hysteresis. This behavior is consistent with experimental evidence showing that temperature gradients can trigger ion-transport-mediated chemical instability in halide perovskites [2]. The dual-peak profile arises from a bulk-to-interface dissipation crossover, while rapid sweeps show efficient heat dissipation because of short thermal dwell time. Neglecting this interaction underestimates transient temperature rises by more than 10 K and misidentifies the scan-rate window associated with S-shaped distortions. Scan-rate-resolved analysis further reveals that ionic screening redistributes internally generated heat toward power-dissipation regions, concentrating losses near interfaces and within transport layers. This localization leads to hotspot formation even under uniform illumination, indicating that ion migration simultaneously screens the internal electric field and modulates the self-heating effects. As a result, Joule heating becomes strongly confined to transport-layer Debye regions adjacent to the perovskite absorber, forming nanometer-scale hotspots and making a nominally bulk loss channel effectively interfacial.

Conclusion and significance: Thermal hysteresis is an operando fingerprint of thermo-electro-ionic dynamics that cannot be inferred from conventional J–V characteristics. The study provides design guidance for interface and transport-layer engineering aimed at mitigating hotspot formations and enhancing the operational stability of PSCs. More broadly, it motivates the explicit inclusion of T–V alongside J–V characteristics as operando stability diagnostics that distinguish ionic-driven hysteresis from thermo-ionic instability pathways. Finally, it provides an initial roadmap for operando experiments to directly measure thermal hysteresis and hotspot precursors.