The efficiency of perovskite solar cells (PSCs) changes over time during storage in a characteristic way:
- Initial Efficiency Improvement: When stored under ambient conditions, PSCs often show an initial increase in power conversion efficiency (PCE), typically within the first couple of days. This improvement is attributed to defect passivation at the perovskite surface, which shifts the charge recombination mechanism from surface-dominated to bulk-dominated. Additionally, the conductivity and energy levels of charge transport layers (like spiro-OMeTAD) improve, enhancing charge extraction and therefore boosting fill factor and open-circuit voltage.
- Longer-Term Stability and Degradation: Beyond the initial period, efficiency can decline due to various degradation mechanisms like iodide oxidation, halide demixing, and general chemical instability of the perovskite layer. However, recent advances in material engineering, such as incorporation of reductive methylhydrazinium cations, have significantly improved stability by reducing defect density, suppressing iodide oxidation, and preventing halide phase segregation. These improvements have enabled PSCs to maintain up to 94% of their initial PCE after prolonged light exposure and elevated temperature testing (e.g., 700 hours), showing much better long-term stability than earlier versions.
In summary, perovskite solar cells typically experience an early-stage efficiency increase during ambient storage due to defect passivation and improved charge extraction, followed by potential efficiency loss over extended times unless advanced stabilization methods are applied. Recent innovations have markedly enhanced both efficiency and storage durability, making PSCs increasingly viable for practical and stable solar energy applications.
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