Steady-state and time-resolved spectroscopic techniques for investigating defect states in perovskite photovoltaics

Perovskite solar cells (PSCs) have gained substantial attention due to rapidly increasing efficiencies and potential advantages, such as tunable bandgaps and low processing costs. However, the presence of defect states, originating from factors such as ionic vacancies, imperfect interfaces, and grain boundaries, currently restricts their performance potential and operational stability. Mitigating these defects is therefore critical for advancing PSC technology toward commercial viability. Both conventional and advanced implementations of photoluminescence and absorption spectroscopies—ranging from steady-state measurements to time-resolved techniques—have become indispensable tools for probing these defect states with high sensitivity, providing crucial insights into their nature, energy distribution, and dynamics. Understanding defects through spectroscopy is key to developing effective passivation strategies. This perspective reviews the most extensively adopted steady-state and time-resolved spectroscopic methods for investigating trap density and their impact on carrier recombination in perovskite materials and devices. We emphasize recent advancements in techniques relevant to understanding and improving defect passivation, aiming to provide guidance for continued progress in the field of perovskite photovoltaics.