Although the power conversion efficiency of perovskite solar cells has increased from 3.81% to 22.1% in just 7 years, they still suffer from stability issues, as they degrade upon exposure to moisture, UV light, heat, and bias voltage. We herein examined the degradation of perovskite solar cells in the presence of UV light alone. The cells were exposed to 365 nm UV light for over 1,000 h under inert gas at <0.5 ppm humidity without encapsulation. 1-sun illumination after UV degradation resulted in recovery of the fill factor and power conversion efficiency. Furthermore, during exposure to consecutive UV light, the diminished short circuit current density (J_sc) and EQE continuously restored. 1-sun light soaking induced recovery is considered to be caused by resolving of stacked charges and defect state neutralization. The J_sc and EQE bounce-back phenomenon is attributed to the beneficial effects of PbI₂ which is generated by the decomposition of perovskite material.

In this study, we employ a combination of various in-situ surface analysis techniques to investigate the thermally induced degradation processes in MAPbI₃ perovskite solar cells (PeSCs) as a function of temperature under air-free conditions (no moisture and oxygen). Through a comprehensive approach that combines in-situ grazing-incidence wide-angle X-ray diffraction (GIWAXD) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) measurements, we confirm that the surface structure of MAPbI₃ perovskite film changes to an intermediate phase and decomposes to CH₃I, NH₃, and PbI₂ after both a short (20 min) exposure to heat stress at 100 °C and a long exposure (>1 hour) at 80 °C. Moreover, we observe clearly the changes in the orientation of CH₃NH₃⁺ organic cations with respect to the substrate in the intermediate phase, which might be linked directly to the thermal degradation processes in MAPbI₃ perovskites. These results provide important progress towards improved understanding of the thermal degradation mechanisms in perovskite materials and will facilitate improvements in the design and fabrication of perovskite solar cells with better thermal stability.

Organic-inorganic hybrid perovskite solar cells (PSCs) have been extensively studied because of their outstanding performance: a power conversion efficiency exceeding 22% has been achieved. The most commonly used PSCs consist of CH₃NH₃PbI₃ (MAPbI₃) with a hole-selective contact, such as 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spiro-bifluorene (spiro-OMeTAD), for collecting holes. From the perspective of long-term operation of solar cells, the cell performance and constituent layers (MAPbI₃, spiro-OMeTAD, etc.) may be influenced by external conditions like temperature, light, etc. Herein, we report the effects of temperature on spiro-OMeTAD and the interface between MAPbI₃ and spiro-OMeTAD in a solar cell. It was confirmed that, at high temperatures (85 °C), I⁻ and CH₃NH₃⁺ (MA⁺) diffused into the spiro-OMeTAD layer in the form of CH₃NH₃I (MAI). The diffused I⁻ ions prevented oxidation of spiro-OMeTAD, thereby degrading the electrical properties of spiro-OMeTAD. Since ion diffusion can occur during outdoor operation, the structural design of PSCs must be considered to achieve long-term stability.

In a PV module, the relative humidity (rh) of a front encapsulant is different from that of a backside encapsulant (rh_back). In this study, the effective humidity (rh_eff) in a PV module was investigated to study the effects of moisture variation on the degradation rate (RD). rh_effrepresents uniform humidity in a PV module when it is exposed to certain damp heat conditions. Five types of accelerated tests were conducted to derive the relation between rh_effand rh_back. rh_effshowed a linear relationship with rh_backat constant temperature. Two types of models, namely, Eyring and Peck models, were used for predicting theRDof PV modules, and their results were compared. TheRDof PV modules was thermally activated at 0.49 eV. Furthermore, the temperature and rh_effhistory of PV modules over one year were determined at two locations: Miami (FL, USA) and Phoenix (AZ, USA). The accumulatedRDvalues based on the temperature and rh_effof the modules were calculated by summing the hourly degradation amounts over the time history.