Approaches to boost the efficiency and stability of perovskite solar cells often address one singular problem in a specific device configuration. In this work, we utilize a poly(ionic-liquid) (PIL) to...
Recent advancements in perovskite
solar cell performance were achieved
by stabilizing the α-phase of FAPbI3 in nip-type architectures. However, these advancements could not be directly
translated to pin-type devices. Here, we fabricated
a high-quality double cation perovskite (MA0.07FA0.93PbI3) with low bandgap energy (1.54 eV) using a two-step
approach on a standard polymer (PTAA). The perovskite films exhibit
large grains (∼1 μm), high external photoluminescence
quantum yields of 20%, and outstanding Shockley–Read–Hall
carrier lifetimes of 18.2 μs without further passivation. The
exceptional optoelectronic quality of the neat material was translated
into efficient pin-type cells (up to 22.5%) with
improved stability under illumination. The low-gap cells stand out
by their high fill factor (∼83%) due to reduced charge transport
losses and short-circuit currents >24 mA cm–2. Using
intensity-dependent quasi-Fermi level splitting measurements, we quantify
an implied efficiency of 28.4% in the neat material, which can be
realized by minimizing interfacial recombination and optical losses.
This work investigates halide segregation
in methylammonium-free
wide bandgap perovskites by photoluminescence quantum yield
(PLQY) and advanced electron microscopy techniques. Our study reveals
how the formation of nano-emitting low-energy domains embedded in
a wide bandgap matrix, located at surfaces and grain boundaries, enables
a PLQY up to 25%. Intensity-dependent PLQY measurement and PL excitation
spectroscopy revealed efficient charge funnelling and the failure
of optical reciprocity between absorption and emission, limiting the
use of PLQY data to determine the quasi-Fermi level splitting (QFLS)
in these layers. Concomitantly, the small spectral overlap between
emission and absorption reduces photon re-absorption. We demonstrate
that phase segregation and charge funnelling, although harmful for
the radiative efficiency of the mixed phase, are essential for achieving
high PLQYs, selectively at low energies, otherwise not achievable
in non-segregated perovskites with a similar bandgap. This promotes
the applicability of this phenomenon in thermally stable high-efficiency
emitting devices and color-conversion heterostructures.
Thin‐film solar cells based on Cu(In,Ga)Se2 (CIGSe) absorber layers reach conversion efficiencies of above 20%. One key to this success is the incorporation of alkali metals, such as Na and K, into the surface and the volume of the CIGSe thin film. The present work discusses the impact of Na and K on the grain‐boundary (GB) properties in CIGSe thin films, i.e., on the barriers for charge carriers, Φb, and on the recombination velocities at the GBs, sGB. First, the physics connected with these two quantities as well as their impact on the device performance are revised, and then the values for the barrier heights and recombination velocities are provided from the literature. The sGB values are measured by means of a cathodoluminescence analysis of Na‐/K‐free CIGSe layers as well as on CIGSe layers on Mo/sapphire substrates, which are submitted to only NaF or only KF postdeposition treatments. Overall, passivating effects on GBs by neither Na nor K can be confirmed. The GB recombination velocities seem to remain on the same order of magnitude, in average about 103–104 cm s−1, irrespective of whether CIGSe thin films are Na‐/K‐free or Na‐/K‐containing.
Hybrid organic–inorganic networks that incorporate
chiral
molecules have attracted great attention due to their potential in
semiconductor lighting applications and optical communication. Here,
we introduce a chiral organic molecule (R)/(S)-1-cyclohexylethylamine (CHEA) into bismuth-based lead-free
structures with an edge-sharing octahedral motif, to synthesize chiral
lead-free (R)/(S)-CHEA4Bi2Br
x
I10–x
crystals and thin films. Using single-crystal X-ray
diffraction measurements and density functional theory calculations,
we identify crystal and electronic band structures. We investigate
the materials’ optical properties and find circular dichroism,
which we tune by the bromide–iodide ratio over a wide wavelength
range, from 300 to 500 nm. We further employ transient absorption
spectroscopy and time-correlated single photon counting to investigate
charge carrier dynamics, which show long-lived excitations with optically
induced chirality memory up to tens of nanosecond timescales. Our
demonstration of chirality memory in a color-tunable chiral lead-free
semiconductor opens a new avenue for the discovery of high-performance,
lead-free spintronic materials with chiroptical functionalities.
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