Photovoltaic solar cells based on metal halide perovskites have gained considerable attention over the past decade because of their potentially low production cost, earth-abundant raw materials, ease of fabrication and ever-increasing power conversion efficiencies of up to 25.2%. This type of solar cells offers the promise of generating electricity at a more competitive unit price than traditional fossil fuels by 2035. Nevertheless, the best research cell efficiencies are still below the theoretical limit defined by the Shockley-Queissier theory owing to the presence of non-radiative recombination losses. In this Review, we analyse the predominant pathways that contribute to non-radiative recombination losses in perovskite solar cells, and evaluate their impact on device performance. We then discuss how non-radiative recombination losses can be estimated through reliable characterization techniques, and highlight some notable advances in mitigating these losses, which hint at pathways towards defect-free perovskite solar cells. Finally, we outline directions for future work that will push the efficiency of perovskite solar cells towards the radiative limit.

Minimizing non-radiative recombination losses in perovskite solar cells

A Realistic Methodology for 30% Efficient Perovskite Solar Cells

Subwavelength particles supporting Mie resonances underpin a strategy in nanophotonics for efficient control and manipulation of light by employing both an electric and a magnetic optically induced multipolar resonant response. Here, we demonstrate that monolithic dielectric nanoparticles made of CsPbBr3 halide perovskites can exhibit both efficient Mie-resonant lasing and structural coloring in the visible and near-IR frequency ranges. We employ a simple chemical synthesis with nearly epitaxial quality for fabricating subwavelength cubes with high optical gain and demonstrate single-mode lasing governed by the Mie resonances from nanocubes as small as 310 nm by the side length. These active nanoantennas represent the most compact room-temperature nonplasmonic nanolasers demonstrated until now.

Room-Temperature Lasing from Mie-Resonant Nonplasmonic Nanoparticles.

The production of large single-crystal metal foils with various facet indices has long been a pursuit in materials science owing to their potential applications in crystal epitaxy, catalysis, electronics and thermal engineering1–5. For a given metal, there are only three sets of low-index facets ({100}, {110} and {111}). In comparison, high-index facets are in principle infinite and could afford richer surface structures and properties. However, the controlled preparation of single-crystal foils with high-index facets is challenging, because they are neither thermodynamically6,7 nor kinetically3 favourable compared to low-index facets6–18. Here we report a seeded growth technique for building a library of single-crystal copper foils with sizes of about 30 × 20 square centimetres and more than 30 kinds of facet. A mild pre-oxidation of polycrystalline copper foils, followed by annealing in a reducing atmosphere, leads to the growth of high-index copper facets that cover almost the entire foil and have the potential of growing to lengths of several metres. The creation of oxide surface layers on our foils means that surface energy minimization is not a key determinant of facet selection for growth, as is usually the case. Instead, facet selection is dictated randomly by the facet of the largest grain (irrespective of its surface energy), which consumes smaller grains and eliminates grain boundaries. Our high-index foils can be used as seeds for the growth of other Cu foils along either the in-plane or the out-of-plane direction. We show that this technique is also applicable to the growth of high-index single-crystal nickel foils, and we explore the possibility of using our high-index copper foils as substrates for the epitaxial growth of two-dimensional materials. Other applications are expected in selective catalysis, low-impedance electrical conduction and heat dissipation. Large-area single-crystal high-index copper and nickel foils with several types of facet are fabricated using mild pre-oxidation of the metal foil surface followed by annealing in a reducing atmosphere.

Seeded growth of large single-crystal copper foils with high-index facets

With tunable pore size and rich active metal centers, metal–organic frameworks (MOFs) have been regarded as the one of the promising materials for catalysis. Prospectively, employing MOFs in electr...

Epitaxial Growth and Integration of Insulating Metal–Organic Frameworks in Electrochemistry

Spin-coated films, such as photoresists for lithography or perovskite films for solar cells, are either amorphous or polycrystalline. We show that epitaxial films of inorganic materials such as cesium lead bromide (CsPbBr3), lead(II) iodide (PbI2), zinc oxide (ZnO), and sodium chloride (NaCl) can be deposited onto a variety of single-crystal and single-crystal-like substrates by simply spin coating either solutions of the material or precursors to the material. The out-of-plane and in-plane orientations of the spin-coated films are determined by the substrate. The thin stagnant layer of supersaturated solution produced during spin coating promotes heterogeneous nucleation of the material onto the single-crystal substrate over homogeneous nucleation in the bulk solution, and ordered anion adlayers may lower the activation energy for nucleation on the surface. The method can be used to produce functional materials such as inorganic semiconductors or to deposit water-soluble materials such as NaCl that can serve as growth templates.

Spin coating epitaxial films.

Surfaces of achiral materials exhibit two-dimensional chirality if they lack mirror symmetry. An example is the (643) surface of face-centered-cubic metals such as Au. The (643) and (643) surfaces are non-superimposable mirror images of each other. Chiral surfaces offer the possibility of serving as heterogeneous catalysts for chiral synthesis or providing a platform for chiral separation or crystallization. Here, we show the symmetry requirements for surface chirality, and we demonstrate that chiral surfaces can be produced by electrochemically depositing epitaxial films of Au onto commercially available Si(643) wafers. Au(643) is deposited onto one side of the wafer, and its enantiomer Au(643) is deposited on the other side of the wafer. In addition to the (643) orientation, the (8 14 17) orientation of Au is produced on the Si(643) wafers. The (8 14 17) orientation has a similar kinked surface to the (643) surface, but it has staggered kinks. Other metal films including Pt, Ni, Cu, and Ag that ar...

Epitaxial Electrodeposition of Chiral Metal Surfaces on Silicon(643).

The expansion of future optoelectronic materials into transparent flexible electronics, perovskite, organic, and tandem photovoltaics depends on the development of high-performance p-type materials...

Epitaxial Electrodeposition of Optically Transparent Hole-Conducting CuI on n-Si(111)


 Cuprous halides are an important class of wide bandgap p-type semiconductors used in opto-electronics. Cuprous bromide (CuBr) shows potential for short-wavelength devices due to a large exciton binding energy (108 meV) and near-ultraviolet bandgap (3.1 eV). However, the growth of high-quality epitaxial CuBr films by electrodeposition has remained a challenge. Here, we introduce a low-cost electrochemical procedure for producing epitaxial CuBr(111) on a Ag(111) substrate by a [111]-oriented silver bromide (AgBr) buffer layer. The AgBr buffer layer forms during the electrodeposition of the CuBr. The mismatch between CuBr(111) and AgBr(111) is -1.3%. A plausible mechanism for nucleation and growth of the epitaxial CuBr is proposed. X-ray techniques including high-resolution X-ray diffraction and X-ray pole figures are used to determine the epitaxial relationship. CuBr(100) is also produced on a Ag(100) surface by a AgBr(100) buffer layer that is rotated in-plane 45° relative to the Ag(100) surface. This in-plane rotation reduces the lattice mismatch from +39.5% for an unrotated film to -1.4% for a 45° rotated film.

Epitaxial Electrodeposition of Wide Bandgap Cuprous Bromide on Silver via a Silver Bromide Buffer Layer

Lu and Tang claim that the spin-coated films in our study are not epitaxial. They assume that all of the background intensity in the x-ray pole figures of the spin-coated materials is due to randomly oriented grains. There is no evidence for randomly oriented grains in the 2θ x-ray patterns. The background intensity in the pole figures is also comparable to the background from the single-crystal substrates, which is inconsistent with their assumption.

https://science.sciencemag.org/content/sci/365/6458/eaay3966.full.pdf

John Z. Tubbesing

Papers

Spin coating epitaxial films.

Epitaxial Electrodeposition of Chiral Metal Surfaces on Silicon(643).

Epitaxial Electrodeposition of Optically Transparent Hole-Conducting CuI on n-Si(111)

Epitaxial Electrodeposition of Wide Bandgap Cuprous Bromide on Silver via a Silver Bromide Buffer Layer

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