Extensive research were conducted to enhance the efficiency of perovskite solar devices, where they are achieving performance record of 25.7% and 33.7% for single junction and tandem PK/Si respectively [1]. Nonetheless, the challenge for their commercial remains on the long-terms stability. Predominantly, research efforts have been focusing upon aging under controlled environments, namely, light soaking and damp heat. In contrast, as reported in literature that the degradation trend observed under continuous illumination may be different than those experienced in real-world operating environments [2]. Additionally, other accelerated stress factors, such as temperature, light cycling, or reverse bias, can affect perovskite materials in distinct ways. However, there is still a lack of clear understanding of the behavior of perovskite devices when analyzed from multiple perspectives.

Accordingly, this study focuses on assessing the stability and performance of perovskite devices under multiple stress factors. Several ISOS protocols were employed, including ISOS-O-3 for outdoor testing, ISOS-LT-3 for thermal cycling, ISOS-LC-3 for indoor light-dark cycling, ISOS-V for reverse bias degradation, as well as ISOS-L-1 and ISOS-L-2 for assessing light and temperature stability [3]. The research particularly focuses on examining the metastable behavior of perovskite-based cells under real operational conditions and indoor day night cycle. It also investigates the temperature coefficient in outdoor environments and through indoor solar-thermal cycling tests. The study was conducted on multiple semi-transparent samples, each comprising eight cells each (multi-cells). Individual cells were analyzed instead of entire modules to avoid cross-behavior effects among different cells within a module and to achieve better statistical reliability.  All devices featured a p-i-n configuration with the following layer stack: fluorine-doped tin oxide (FTO), nickel oxide (NiO), self-assembled monolayer (SAM) (MeO-2PACz), a perovskite layer (3C), C60, tin oxide (SnO₂), and indium tin oxide (ITO). The samples were encapsulated in glass-glass configuration with polyisobutylene (PIB) serving as an edge sealant.

Degradation was observed to occur predominantly at the beginning of the test, with both the duration and level of degradation varying depending on the applied stress factors. Notably, two distinct recovery mechanisms were identified. First, recovery was observed under outdoor day-night cycles and during indoor accelerated tests, likely due to the formation of charge extraction barriers or the creation and passivation of metastable defects, commonly observed for perovskite [4] [5]. Second, a more gradual recovery of electrical performance to near-initial values was noted over extended periods, exceeding several weeks of operation. This highlights the presence of fully reversible defects.

Temperature cycling further revealed a significant reduction in the fill factor (FF) at low temperatures (<40°C), whereas higher temperatures showed no such changes. Using drift-diffusion modeling approach, the FF reduction was linked to an increased activated defect density in the bulk at low temperatures. Additionally, the temperature coefficient for Jsc and Voc exhibited typical values aligned with conventional technologies. However, efficiency demonstrated a double trend within the temperature range of 5–85°C, shifting from a positive to a negative coefficient. The threshold for this inversion correlated with the degradation level of the devices, reinforcing calculation from outdoor testing. In summary, gaining a deeper understanding of perovskite failure mechanisms and their response to environmental conditions requires accelerated aging tests under various stress factors, along with the combination of different testing protocols.