Deciphering UV-Induced Ionic-Electronic Degradation in Metal Oxide-Free p–i–n Perovskite Solar Cells under Inert Conditions

Perovskite solar cells are currently well known for both their outstanding advantages and their main drawback: rapid degradation when exposed to external agents. In particular, the sensitivity of these devices to ultraviolet (UV) radiation has been widely reported, where the underlying degradation mechanisms in metal oxide-free p–i–n architectures remain insufficiently understood. In this work, we systematically investigate the impact of UV irradiation (385 nm) on metal oxide-free p–i–n PSCs under inert atmosphere, combining optical simulations, morphological characterization (SEM and AFM), current-voltage analysis, scan-rate-dependent measurements, and impedance spectroscopy. Optical modeling reveals that UV photons are absorbed within the first few tens of nanometers of the perovskite layer, near the hole transport layer (HTL)/perovskite interface. Consistently, SEM and AFM analyses show significant surface restructuring after UV exposure, including grain coarsening and increased roughness. Electrically, degradation is dominated by a severe loss of short-circuit current density, accompanied by a progressive reduction in fill factor, while the open-circuit voltage remains comparatively stable. Detailed DC and AC analyses demonstrate that these effects originate from a coupled ionic-electronic degradation mechanism. UV exposure promotes the accumulation of mobile ions, leading to screening of the internal electric field and impaired charge extraction, while simultaneously generating deep trap states at or near the HTL/perovskite interface that enhance Shockley-Read-Hall recombination. Impedance spectroscopy further reveals increased ionic transport and the emergence of fast interfacial processes associated with trap-assisted recombination. These findings provide a comprehensive mechanistic framework for understanding UV-induced degradation in metal oxide-free p–i–n perovskite solar cells and highlight the critical role of interfacial ion-trap interactions in limiting device stability, even under inert and encapsulated operating conditions.