The power conversion efficiency of perovskite solar cells (PSCs) has ascended from 3.8% to 22.1% in recent years. ZnO has been well-documented as an excellent electron-transport material. However, the poor chemical compatibility between ZnO and organo-metal halide perovskite makes it highly challenging to obtain highly efficient and stable PSCs using ZnO as the electron-transport layer. It is demonstrated in this work that the surface passivation of ZnO by a thin layer of MgO and protonated ethanolamine (EA) readily makes ZnO as a very promising electron-transporting material for creating hysteresis-free, efficient, and stable PSCs. Systematic studies in this work reveal several important roles of the modification: (i) MgO inhibits the interfacial charge recombination, and thus enhances cell performance and stability; (ii) the protonated EA promotes the effective electron transport from perovskite to ZnO, further fully eliminating PSCs hysteresis; (iii) the modification makes ZnO compatible with perovskite, nicely resolving the instability of ZnO/perovskite interface. With all these findings, PSCs with the best efficiency up to 21.1% and no hysteresis are successfully fabricated. PSCs stable in air for more than 300 h are achieved when graphene is used to further encapsulate the cells.
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.
Perovskite
solar cells are strong competitors for silicon-based
ones, but suffer from poor long-term stability, for which the intrinsic
stability of perovskite materials is of primary concern. Herein, we
prepared a series of well-defined cesium-containing mixed cation and
mixed halide perovskite single-crystal alloys, which enabled systematic
investigations on their structural stabilities against light, heat,
water, and oxygen. Two potential phase separation processes are evidenced
for the alloys as the cesium content increases to 10% and/or bromide
to 15%. Eventually, a highly stable new composition, (FAPbI3)0.9(MAPbBr3)0.05(CsPbBr3)0.05, emerges with a carrier lifetime of 16 μs.
It remains stable during at least 10 000 h water–oxygen
and 1000 h light stability tests, which is very promising for long-term
stable devices with high efficiency. The mechanism for the enhanced
stability is elucidated through detailed single-crystal structure
analysis. Our work provides a single-crystal-based paradigm for stability
investigation, leading to the discovery of stable new perovskite materials.
OSW-1 (1), an acylated disaccharide cholestane saponin from Ornithogalum saudersiae with exceptionally potent antitumor activity, was first synthesized from commercially available dehydroisoandrosterone, L-arabinose, and D-xylose in total 27 steps with the longest linear sequence of 14 steps and in 6% yield.
Owing
to the ionic nature of lead halide perovskites, their halide-terminated
surface is unstable under light-, thermal-, moisture-, or electric-field-driven
stresses, resulting in the formation of unfavorable surface defects.
As a result, nonradiative recombination generally occurs on perovskite
films and deteriorates the efficiency, stability, and hysteresis performances
of perovskite solar cells (PSCs). Here, a surface iodide management
strategy was developed through the use of cesium sulfonate to stabilize
the perovskite surface. It was found that the pristine surface of
common perovskite was terminated with extra iodide, that is, with
an I–/Pb2+ ratio larger than 3, explaining
the origination of surface-related problems. Through post-treatment
of perovskite films by cesium sulfonate, the extra iodide on the surface
was facilely removed and the as-exposed Pb2+ cations were
chelated with sulfonate anions while maintaining the original 3D perovskite
structure. Such iodide replacement and lead chelating coordination
on perovskite could reduce the commonly existing surface defects and
nonradiative recombination, enabling assembled PSCs with an efficiency
of 22.06% in 0.12 cm2 cells and 18.1% in 36 cm2 modules with high stability.
Crown ether effectively stabilizes the cubic phase of CsPbI3 to inhibit the moisture invasion and phase transformation of CsPbI3 films, producing large-area devices and improving device performance.
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