A significant
fraction of global electricity demand is for lighting.
Enabled by the realization and development of efficient GaN blue light-emitting
diodes (LEDs), phosphor-based solid-state white LEDs provide a much
higher efficiency alternative to incandescent and fluorescent lighting,
which are being broadly implemented. However, a key challenge for
this industry is to achieve the right photometric ranges and application-specific
emission spectra via cost-effective means. Here, we synthesize organic–inorganic
lead halide-based perovskite crystals with broad spectral tuneability.
By tailoring the composition of methyl and octlyammonium cations in
the colloidal synthesis, meso- to nanoscale 3D crystals (5–50
nm) can be formed with enhanced photoluminescence efficiency. By increasing
the octlyammonium cations content, we observe platelet formation of
2D layered perovskite sheets; however, these platelets appear to be
less emissive than the 3D crystals. We further manipulate the halide
composition of the perovskite crystals to achieve emission covering
the entire visible spectrum. By blending perovskite crystals with
different emission wavelengths in a polymer host, we demonstrate the
potential to replace conventional phosphors and provide the means
to replicate natural white light when excited by a blue GaN LED.
We demonstrate a method for controlled p-doping of the halide perovskite surface using molecular dopants, resulting in reduced non-radiative recombination losses and improved device performance.
Metal halide perovskite
solar cells have now reached efficiencies
of over 22%. To date, the most efficient perovskite solar cells have
the n-i-p device architecture and use 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene
or poly(triarylamine) as the hole transport material (HTM), which
are typically doped with lithium bis((trifluomethyl)sulfonyl)amide
(Li-TFSI). Li-TFSI is hygroscopic and detrimental to the long-term
performance of the solar cells, limiting its practical use. In this
work, we successfully replace Li-TFSI by molybdenum tris(1-(methoxycarbonyl)-2-(trifluoromethyl)ethane-1,2-dithiolene),
Mo(tfd-CO2Me)3, or molybdenum tris(1-(trifluoroacetyl)-2-(trifluoromethyl)ethane-1,2-dithiolene),
Mo(tfd-COCF3)3. With these two dopants, we achieve
stabilized power conversion efficiencies up to 16.7% and 15.7% with
average efficiencies of 14.8% ± 1.1% and 14.4% ± 1.2%, respectively.
Moreover, we observe a significant enhancement of the long-term stability
of perovskite solar cells under 85 °C thermal stressing in air.
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