Contemporary
thin-film photovoltaic (PV) materials contain elements
that are scarce (CIGS) or regulated (CdTe and lead-based perovskites),
a fact that may limit the widespread impact of these emerging PV technologies.
Tin halide perovskites utilize materials less stringently regulated
than the lead (Pb) employed in mainstream perovskite solar cells;
however, even today’s best tin-halide perovskite thin films
suffer from limited carrier diffusion length and poor film morphology.
We devised a synthetic route to enable in situ reaction between metallic
Sn and I2 in dimethyl sulfoxide (DMSO), a reaction that
generates a highly coordinated SnI2·(DMSO)
x
adduct that is well-dispersed in the precursor solution.
The adduct directs out-of-plane crystal orientation and achieves a
more homogeneous structure in polycrystalline perovskite thin films.
This approach improves the electron diffusion length of tin-halide
perovskite to 290 ± 20 nm compared to 210 ± 20 nm in reference
films. We fabricate tin-halide perovskite solar cells with a power
conversion efficiency of 14.6% as certified in an independent lab.
This represents a ∼20% increase compared to the previous best-performing
certified tin-halide perovskite solar cells. The cells outperform
prior earth-abundant and heavy-metal-free inorganic-active-layer-based
thin-film solar cells such as those based on amorphous silicon, Cu2ZnSn(S/Se)4 , and Sb2(S/Se)3.
Tin
oxide (SnO2) has recently emerged as a promising
electron transport layer for perovskite solar cells (PSCs) in light
of the material’s optical and electronic properties and its
low-temperature processing. However, SnO2 films are prone
to surface defect formation, which results in energy loss in PSCs.
We report that surface treatment using ammonium fluoride (NH4F) leads to reduced surface defects and that it also induces chemical
doping of the SnO2 substrate simultaneously. The effects
of NH4F treatment on SnO2 properties are revealed
by surface chemical analysis, computational studies, and energy level
investigations, and PSCs with the treatment achieve photovoltaic performance
of 23.2% in light of higher voltage than in relevant controls.
Many of the best-performing perovskite photovoltaic devices make use of 2D/3D interfaces, which improve efficiency and stability – but it remains unclear how the conversion of 3D-to-2D perovskite occurs and how these interfaces are assembled. Here, we use in situ Grazing-Incidence Wide-Angle X-Ray Scattering to resolve 2D/3D interface formation during spin-coating. We observe progressive dimensional reduction from 3D to n = 3 → 2 → 1 when we expose (MAPbBr3)0.05(FAPbI3)0.95 perovskites to vinylbenzylammonium ligand cations. Density functional theory simulations suggest ligands incorporate sequentially into the 3D lattice, driven by phenyl ring stacking, progressively bisecting the 3D perovskite into lower-dimensional fragments to form stable interfaces. Slowing the 2D/3D transformation with higher concentrations of antisolvent yields thinner 2D layers formed conformally onto 3D grains, improving carrier extraction and device efficiency (20% 3D-only, 22% 2D/3D). Controlling this progressive dimensional reduction has potential to further improve the performance of 2D/3D perovskite photovoltaics.
The open‐circuit voltage (Voc) of perovskite solar cells is limited by non‐radiative recombination at perovskite/carrier transport layer (CTL) interfaces. 2D perovskite post‐treatments offer a means to passivate the top interface; whereas, accessing and passivating the buried interface underneath the perovskite film requires new material synthesis strategies. It is posited that perovskite ink containing species that bind strongly to substrates can spontaneously form a passivating layer with the bottom CTL. The concept using organic spacer cations with rich NH2 groups is implemented, where readily available hydrogens have large binding affinity to under‐coordinated oxygens on the metal oxide substrate surface, inducing preferential crystallization of a thin 2D layer at the buried interface. The passivation effect of this 2D layer is examined using steady‐state and time‐resolved photoluminescence spectroscopy: the 2D interlayer suppresses non‐radiative recombination at the buried perovskite/CTL interface, leading to a 72% reduction in surface recombination velocity. This strategy enables a 65 mV increase in Voc for NiOx based p–i–n devices, and a 100 mV increase in Voc for SnO2‐based n–i–p devices. Inverted solar cells with 20.1% power conversion efficiency (PCE) for 1.70 eV and 22.9% PCE for 1.55 eV bandgap perovskites are demonstrated.
The epitaxial growth of a perovskite
matrix on quantum dots (QDs)
has enabled the emergence of efficient red light-emitting diodes (LEDs)
because it unites efficient charge transport with strong surface passivation.
However, the synthesis of wide-band gap (E
g) QD-in-matrix heterostructures has so far remained elusive in the
case of sky-blue LEDs. Here, we developed CsPbBr3 QD-in-perovskite
matrix solids that enable high luminescent efficiency and spectral
stability with an optical E
g of over 2.6
eV. We screened alloy candidates that modulate the perovskite E
g and allow heteroepitaxy, seeking to implement
lattice-matched type-I band alignment. Specifically, we introduced
a CsPb1–x
Sr
x
Br3 matrix, in which alloying with Sr2+ increased the E
g of the perovskite and
minimized lattice mismatch. We then developed an approach to passivation
that would overcome the hygroscopic nature of Sr2+. We
found that bis(4-fluorophenyl)phenylphosphine oxide
strongly coordinates with Sr2+ and provides steric hindrance
to block H2O, a finding obtained by combining molecular
dynamics simulations with experimental results. The resulting QD-in-matrix
solids exhibit enhanced air- and photo-stability with efficient charge
transport from the matrix to the QDs. LEDs made from this material
exhibit an external quantum efficiency of 13.8% and a brightness exceeding
6000 cd m–2.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.