Perovskite
solar cells (PSCs) have reached certified efficiencies
of up to 23.7% but suffered from frailness and instability when exposed
to ambient atmosphere. Zinc oxide (ZnO), when used as electron transport
layer (ETL) on PSCs, gives rise to excellent electronic, optic, and
photonic properties, yet the Lewis basic nature of ZnO surface leads
to deprotonation of the perovskite layer, resulting in serious degradation
of PSCs using ZnO as ETL. Here, we report a simple but effective strategy
to convert ZnO surface into ZnS at the ZnO/perovskite interface by
sulfidation. The sulfide on ZnO–ZnS surface binds strongly
with Pb2+ and creates a novel pathway of electron transport
to accelerate electron transfer and reduce interfacial charge recombination,
yielding a champion efficiency of 20.7% with improved stability and
no appreciable hysteresis. The model devices modified with sulfide
maintained 88% of their initial performance for 1000 h under storage
condition and 87% for 500 h under UV radiation. ZnS is demonstrated
to act as both a cascade ETL and a passivating layer for enhancing
the performance of PSCs.
With the rapid development, mass production, and pervasive distribution of smartphones in recent years, they have provided people with portable, cost-effective, and easy-to-operate platforms to build analytical biosensors for point-of-care (POC) applications and mobile health.
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