Ambient storage of perovskite solar cells (PSCs) has been observed to affect both the fill factor (FF) and open-circuit voltage (VOC) positively in the short term. Key findings include:
- Improvement in Fill Factor and VOC: During the first couple of days of ambient storage, typical n-i-p PSCs show an increase in both FF and VOC, leading to an overall improvement in power conversion efficiency (PCE).
- Mechanism – Defect Passivation: This improvement is attributed primarily to defect passivation at the perovskite surface, which reduces surface recombination losses. As a result, the dominant charge recombination mechanism shifts from surface-dominated to bulk-dominated recombination, reducing losses and enhancing VOC.
- Enhanced Charge Extraction: Ambient storage also improves the conductivity of the hole transport layer (typically spiro-OMeTAD) and lowers its highest occupied molecular orbital level. This enhances charge extraction efficiency, contributing further to improved FF and VOC.
- Dependence on Film Stability and Morphology: The extent and sustainability of these improvements depend on perovskite film moisture resistance, grain morphology, trap density, and device architecture. Proper chemical additives and solvent engineering used during ambient condition processing can yield films with large crystal grains and low trap densities, supporting long-term stability and performance retention even after months of storage.
In summary, ambient storage initially enhances the fill factor and open-circuit voltage of perovskite solar cells primarily by passivating surface defects and improving charge transport layers, thereby reducing recombination losses and improving charge extraction. This effect can stabilize and improve device performance if the perovskite film and device architecture are optimized to resist degradation from moisture and oxygen in ambient conditions.
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