The main environmental factors that degrade perovskite materials, particularly in perovskite solar cells, are:
- Moisture (humidity): Water molecules react chemically with perovskite materials such as methylammonium lead iodide (MAPbI3), causing hydrolysis and breaking down the crystal structure. This leads to decomposition into lead iodide (PbI2), methylammonium iodide (MAI), and volatile compounds like methylamine and hydrogen iodide. Moisture induces lattice distortion, transforming the perovskite’s 3D structure into less stable lower-dimensional phases, accelerating degradation.
- Oxygen: Oxygen often works synergistically with moisture to oxidize components of the perovskite, speeding degradation. Oxygen can interact with hydrogen iodide formed during decomposition, producing iodine and water, which furthers the breakdown process.
- Ultraviolet (UV) light: Exposure to UV light induces photochemical reactions that damage the perovskite and surrounding layers, like the electron transport layer (ETL). UV can generate trap states in ETLs such as TiO2, lowering device performance and contributing to degradation. Using alternative ETL materials (e.g., Al-doped TiO2 or SnO2) can mitigate this UV-induced degradation.
- High temperature: Elevated temperatures accelerate chemical decomposition and promote the formation of structural defects. Heat stress, especially when combined with oxygen and moisture, results in rapid degradation of perovskite films.
- Environmental ambient conditions: Ambient atmosphere containing oxygen and humidity accelerates degradation compared to inert or controlled atmospheres, also influencing film quality due to defect formation during fabrication.
In summary, perovskite materials degrade mainly due to moisture, oxygen, UV light, and heat, often in combination. These factors cause chemical decomposition, structural changes, and defect formation, leading to rapid loss of performance and material integrity.
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