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.
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.
Perovskite
solar cells (PSCs) with organic hole transporting layers
(o-HTLs) have been widely studied due to their convenient solution
processing, but it remains a big challenge to improve the hole mobilities
of commercially available organic hole transporting materials without
ion doping while maintaining the stability of PSCs. In this work,
we demonstrated that the introduction of perovskite quantum dots (QDs)
as interlayers between perovskite layers and dopant-free o-HTLs (P3HT,
PTAA, Spiro-OMeTAD) resulted in a significantly enhanced performance
of PSCs. The universal role of QDs in improving the efficiency and
stability of PSCs was validated, exceeding that of lithium doping.
After a deep examination of the mechanism, QD interlayers provided
the multifunctional roles as follows: (1) passivating the perovskite
surface to reduce the overall amount of trap states; (2) promoting
hole extraction from perovskite to dopant-free o-HTLs by forming cascade
energy levels; (3) improving hole mobilities of dopant-free o-HTLs
by regulating their polymer/molecule orientation. What is more, the
thermal/moisture/light stabilities of dopant-free o-HTLs-based PSCs
were greatly improved with QD interlayers. Finally, we demonstrated
the reliability of the QD interlayers by fabricating large-area solar
modules with dopant-free o-HTLs, showing great potential in commercial
usage.
Perovskite
films prepared with CH3NH2 molecules
under ambient conditions have led to rapid fabrication of perovskite
solar cells (PSCs), but there remains a lack of mechanistic studies
and inconsistencies with operability in their production. Here the
crystal structure of CH3NH2–CH3NH3PbI3 was analyzed to involve hydrogen bonds
(CH3NH2···CH3NH3
+) and has guided the facile, reproducible preparation
of high-quality perovskite films under ambient conditions. Hydrogen
bonds within CH3NH2···CH3NH3
+ dimers were found in the CH3NH2–CH3NH3PbI3 intermediates, accompanied by 1D-PbI3
– chains (δ-phase). The weakly hydrogen-bonded CH3NH2 molecules were easily released from the CH3NH2–CH3NH3PbI3 intermediates, contributing to rapid, spontaneous phase transition
from 1D-PbI3
– (δ-phase) to 3D-PbI3
– (α-phase). Further introduction
of CH3NH3Cl into the CH3NH2–CH3NH3PbI3 intermediates
led to interruption of 1D-PbI3
– transition
into 0D-Pb2I9‑x
Cl
x
5–(0 < x < 6), adjusting the phase transition route toward 3D-PbI3
–. On the basis of the above understanding,
CH3NH2 solution in ethanol and CH3NH3Cl were used for precursors and a best efficiency of
20.3% in PSCs was achieved. Large-scale modules (12 cm2 aperture area) fabricated by a dip-coating technology exhibited
an efficiency up to 16.0% and outstanding stability over 10 000
s under continuous output. The developed preparation method of perovskite
precursors and insightful research into the methylamine-dimer-induced
phase transition mechanism have enabled the production of high-quality
perovskite films with robust operability, showing great potential
for large-scale commercialization.
Research on solvent chemistry, particularly for halide
perovskite
intermediates, has been advancing the development of perovskite solar
cells (PSCs) toward commercial applications. A predictive understanding
of solvent effects on the perovskite formation is thus essential.
This work systematically discloses the relationship among the basicity
of solvents, solvent-contained intermediate structures, and intermediate-to-perovskite
α-FAPbI3 evolutions. Depending on their basicity,
solvents exhibit their own favorite bonding selection with FA+ or Pb2+ cations by forming either hydrogen bonds
or coordination bonds, resulting in two different kinds of intermediate
structures. While both intermediates can be evolved into α-FAPbI3 below the δ-to-α thermodynamic temperature, the
hydrogen-bond-favorable kind could form defect-less α-FAPbI3 via sidestepping the break of strong coordination bonds.
The disclosed solvent gaming mechanism guides the solvent selection
for fabricating high-quality perovskite films and thus high-performance
PSCs and modules.
As an inorganic hole transport material (HTM), nickel oxide (NiOx) is widely used in perovskite solar cells (PSCs) due to its low cost and intrinsic stability. However, on account of its poor film formation on perovskite, the low power conversion efficiency (PCE) and stability of regular NiOx‐based PSCs is a main obstacle for commercialization. Here, a solution‐processed inorganic/organic hybrid hole transporting system is developed to resolve this issue, thereby improving the PCE from 16.0% to 21.2%. Poly(3‐hexylthiophene) (P3HT) is studied as the typical case, revealing that the performance improvement mainly lies in the synergistic interaction between NiOx and P3HT: 1) the introduction of P3HT improves assembly regularity and film uniformity of NiOx; 2) electron redistribution between P3HT and NiOx increases the Ni3+/Ni2+ ratio for higher hole mobility; 3) the feed‐back impact of NiOx on P3HT enhances molecular orientation of polymer chains in P3HT for better hole transport through polymer framework. Finally, the encapsulated solar cell modules with P3HT‐promoted NiOx maintains 91% of the initial efficiency after 1000 h aging at a harsh 85 °C/85% relative humidity condition. This finding provides a feasible approach for using NiOx‐based HTMs to realize high‐performance regular PSCs, paving the way for their commercialization.
N-Methyl-2-pyrrolidone (NMP), forming only one PbI2·NMP complex, is demonstrated as an excellent coordinative solvent for the fabrication of high-quality perovskite thin films.
α-FAPbI3-based perovskite solar cells have recently
attracted increasing attention as a result of an ideal bandgap and
longer exciton lifetime of FAPbI3 compared to perovskites
with other compositions. However, in a traditional fabrication method,
the α-FAPbI3 films were usually obtained by a direct
phase transition from δ to α phase at a high annealing
temperature, leading to low quality with poor crystallinity and numerous
defects. The formation and stabilization of phase-pure, material-pure,
high-quality α-FAPbI3 films remain challenging. In
this work, a FA vapor-assisted cation-exchange pathway from low-dimensional
perovskites to three-dimensional α-FAPbI3 was built,
through which phase-pure and material-pure α-FAPbI3 films were achieved at 100 °C below the temperature of thermodynamic
δ-to-α phase transition (∼150 °C). Through
an in-depth study, the cation-exchange pathway was found to have a
low reaction barrier directly toward α-FAPbI3 and
suppress the formation of δ-FAPbI3, leading to high-quality
α-FAPbI3 with high orientation and few trap states
at a low annealing temperature. Consequently, small-area devices and
large-area modules with as-prepared α-FAPbI3 films
were achieved with improved performance, showing great potential for
further study and application.
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