Impurity-healing interface engineering for efficient perovskite submodules.

An issue that affects the scaling-up development of perovskite photovoltaics is the marked efficiency drop when enlarging the device area, caused by the inhomogeneous distribution of defected sites. In the narrow band gap formamidinium lead iodide (FAPbI), the native impurities of PbI and δ-FAPbI non-perovskite could induce unfavoured non-radiative recombination, as well as inferior charge transport and extraction. Here we develop an impurity-healing interface engineering strategy to address the issue in small-area solar cells and large-scale submodules.

Post-Treatment-Free Dual-Interface Passivation via Facile 1D/3D Perovskite Heterojunction Construction.

For achieving high-efficiency perovskite solar cells, it is almost always necessary to substantially passivate defects and protect the perovskite structure at its interfaces with charge transport layers. Such a modification generally involves the post-treatment of the deposited perovskite film by spin coating, which cannot meet the technical demands of scaling up the production of perovskite photovoltaics. In this work, we demonstrate one-step construction of buried and capped double 1D/3D heterojunctions without the need for any post-treatment, which is achieved through facile tetraethylammonium trifluoroacetate (TEATFA) prefunctionalization on the SnO substrate.

Surface Termination on Unstable Methylammonium-based Perovskite Using a Steric Barrier for Improved Perovskite Solar Cells.

Compared to widely adopted low-dimensional/three-dimensional (LD/3D) heterostructure, functional organic cation based surface termination on perovskite can not only realize advantage of defect passivation but also prevent potential disadvantage of the heterostructure induced intercalation into 3D perovskite. However, it is still very challenging to controllably construct surface termination on organic-inorganic hybrid perovskite because the functional organic cations' substitution reaction is easy to form LD/3D heterostructure. Here, we report using a novel benzyltrimethylammonium (BTA) functional cation with rational designed steric hindrance to effectively surface terminate onto methylammonium lead triiodide (MAPbI ) perovskite, which is composed of the most unstable MA cations.

Highly Crystalized Cl-Doped SnO Nanocrystals for Stable Aqueous Dispersion Toward High-Performance Perovskite Photovoltaics.

Tin dioxide (SnO ) with high conductivity and low photocatalytic activity has been reported as one of the best candidates for highly efficient electron transport layer (ETL) in perovskite solar cell (PSC). The state-of-the-art SnO layer is achieved by chemical bath deposition with tunable properties, while the commercial SnO nanocrystals (NCs) with low tunability still face the necessity of further improvement. Here, a kind of highly crystallized Cl-doped SnO NCs is reported that can form very stable aqueous dispersion with shelf life up to one year without any stabilizer, which can facilitate the fabrication of PSCs with satisfactory performance.

Myth behind Metastable and Stable -Hexylammonium Bromide-Based Low-Dimensional Perovskites.

In perovskite solar cells, passivating the surface or interface that contains a high concentration of defects, specifically deep-level defects, is one of the most important topics to substantially enhance the power conversion efficiency and stability of the devices. Long-chain alkylammonium bromides have been widely and commonly adapted for passivation treatment. However, the mechanism behind is still not well explored as the formation route and the exact structure of these alkylammonium bromide-based low-dimensional perovskites are unclear.

Functional organic cation induced 3D-to-0D phase transformation and surface reconstruction of CsPbI inorganic perovskite.

Efficiency and stability are the main research focuses for perovskite solar cells. Inorganic perovskites like CsPbI possess higher chemical stability than those with organic A-site cations, while they also exhibit higher defect density. Nonetheless, it is highly challenging to induce orderly secondary arrangement or reconstruction of inorganic perovskites with reduced defects because of their unique chemical properties.

Lattice disorder influences the photocarrier dynamics in lead halide perovskites.

Revealing the structural impact of lead halide perovskites on photocarrier dynamics is essential for the associated solar cells but deficient in experimental visualization. In this study, with femtosecond spectroscopy, we for the first time explored the contribution of the disorder of the distorted PbX octahedrons and A-site cations on the carrier behaviours. It was found that photoinduced carriers recombine almost twice slower and diffuse 20% faster in the disordered, β-phased samples than in the ordered, γ-phased ones.

Decoupling engineering of formamidinium-cesium perovskites for efficient photovoltaics.

Although pure formamidinium iodide perovskite (FAPbI) possesses an optimal gap for photovoltaics, their poor phase stability limits the long-term operational stability of the devices. A promising approach to enhance their phase stability is to incorporate cesium into FAPbI. However, state-of-the-art formamidinium-cesium (FA-Cs) iodide perovskites demonstrate much worse efficiency compared with FAPbI, limited by the different crystallization dynamics of formamidinium and cesium, which result in poor composition homogeneity and high trap densities.

Zwitterion-Functionalized SnO Substrate Induced Sequential Deposition of Black-Phase FAPbI with Rearranged PbI Residue.

Black-phase formamidinium lead iodide (FAPbI ) with narrow bandgap and high thermal stability has emerged as the most promising candidate for highly efficient and stable perovskite photovoltaics. In order to overcome the intrinsic difficulty of black-phase crystallization and to eliminate the lead iodide (PbI ) residue, most sequential deposition methods of FAPbI -based perovskite will introduce external ions like methylammonium (MA ), cesium (Cs ), and bromide (Br ) ions to the perovskite structure. Here a zwitterion-functionalized tin(IV) oxide (SnO ) is introduced as the electron-transport layer (ETL) to induce the crystallization of high-quality black-phase FAPbI .

Stable Pure Iodide MACsPbI Perovskite toward Efficient 1.6 eV Bandgap Photovoltaics.

Perovskite photovoltaics with the advantages of facile fabrication and high efficiency have been the rising star in the field for a decade. Methylammonium lead triiodide (MAPbI) was the first widely studied perovskite to initiate the boom of perovskite photovoltaics, but it was later considered thermodynamically instable for commercialization. Here, we demonstrate that simple cesium (Cs) doping without any complicated process can form a stable MA-based perovskite with a widened bandgap, which may broaden the application of MA-based perovskites in tandem solar cells.

Solution chemistry quasi-epitaxial growth of atomic CaTiO perovskite layers to stabilize and passivate TiO photoelectrodes for efficient water splitting.

Perovskite oxides with unique crystal structures and high defect tolerance are promising as atomic surface passivation layers for photoelectrodes for efficient and stable water splitting. However, controllably depositing and crystalizing perovskite-type metal oxides at the atomic level remains challenging, as they usually crystalize at higher temperatures than regular metal oxides. Here, we report a mild solution chemistry approach for the quasi-epitaxial growth of an atomic CaTiO perovskite layer on rutile TiO nanorod arrays.

Electro-Reforming Polyethylene Terephthalate Plastic to Co-Produce Valued Chemicals and Green Hydrogen.

Upcycling plastic waste pollution for sustainable resources and energy is an ideal solution to plastic waste-related environmental issues. Polyethylene terephthalate (PET), one of the most prominent single-use daily plastics with up to millions of tons produced annually, has recently been explored with respect to chemical recycling to ameliorate its environmental impact. In this work, we report an electrochemical upcycling approach to electrocatalytic oxidation of PET hydrolysate using Cu-based nanowire catalysts.

Deep-Red Perovskite Light-Emitting Diodes Based on One-Step-Formed γ-CsPbI Cuboid Crystallites.

Inorganic CsPbI perovskite with high chemical stability is attractive for efficient deep-red perovskite light-emitting diodes (PeLEDs) with high color purity. Compared to PeLEDs based on ex-situ-synthesized CsPbI nanocrystals/quantum dots suffering from low conductivity and efficiency droop under high current densities, in situ deposited 3D CsPbI films from precursor solutions can maintain high conductivity but show high trap density. Here, it is demonstrated that introducing diammonium iodide can increase the size of colloids in the precursor solution, retard the phase-transition rate, and passivate trap states of the in-situ-formed cuboid crystallites.

Efficient and Stable CsPbI Inorganic Perovskite Photovoltaics Enabled by Crystal Secondary Growth.

Defect-triggered phase degradation is generally considered as the main issue that causes phase instability and limited device performance for CsPbI inorganic perovskites. Here, a defect compensation in CsPbI perovskite through crystal secondary growth of inorganic perovskites is demonstrated, and highly efficient inorganic photovoltaics are realized. This secondary growth is achieved by a solid-state reaction between a bromine salt and defective CsPbI perovskite.

MA Cation-Induced Diffusional Growth of Low-Bandgap FA-Cs Perovskites Driven by Natural Gradient Annealing.

Low-bandgap formamidinium-cesium (FA-Cs) perovskites of FA Cs PbI ( < 0.1) are promising candidates for efficient and robust perovskite solar cells, but their black-phase crystallization is very sensitive to annealing temperature. Unfortunately, the low heat conductivity of the glass substrate builds up a temperature gradient within from bottom to top and makes the initial annealing temperature of the perovskite film lower than the black-phase crystallization point (~150°C).

Organic Matrix Assisted Low-temperature Crystallization of Black Phase Inorganic Perovskites.

All-inorganic perovskites have attracted increasing attention for applications in perovskite solar cells (PSCs) and optoelectronics, including light-emitting devices (LEDs). Cesium lead halide perovskites with tunable I/Br ratios and a band gap aligning with the sunlight region are promising candidates for PSCs. Although impressive progress has been made to improve device efficiency from the initial 2.

Highly Stable Inorganic Lead Halide Perovskite toward Efficient Photovoltaics.

ConspectusOwing to the remarkable progress achieved over the past decade with research efforts from the perspectives of material synthesis, device configuration, and theoretical investigation, metal halide perovskites have emerged as a revolutionary class of light-absorbing semiconductors. The perovskite photovoltaic devices have demonstrated an impressive increase in power conversion efficiency. For single-junction perovskite solar cells, the value has risen from the initial one-digit maximum to the state-of-art record of 25.

Incorporation of Two-Dimensional WSe into MAPbI Perovskite for Efficient and Stable Photovoltaics.

Achieving reduced defect density and efficient charge carrier extraction plays a vital role for efficient and stable perovskite solar cells (PSCs). Over the course of technical development, it is desired to use one single material or approach to synergistically passivate defects and enhance the charge extraction. In this work, we developed an effective strategy for obtaining efficient and stable PSCs via incorporating quasi-monolayer two-dimensional WSe into the MAPbI perovskite layer.

Using steric hindrance to manipulate and stabilize metal halide perovskites for optoelectronics.

The chemical instability of metal halide perovskite materials can be ascribed to their unique properties of softness, in which the chemical bonding between metal halide octahedral frameworks and cations is the weak ionic and hydrogen bonding as in most perovskite structures. Therefore, various strategies have been developed to stabilize the cations and metal halide frameworks, which include incorporating additives, developing two-dimensional perovskites and perovskite nanocrystals, Recently, the important role of utilizing steric hindrance for stabilizing and passivating perovskites has been demonstrated. In this perspective, we summarize the applications of steric hindrance in manipulating and stabilizing perovskites.

Organic Tetrabutylammonium Cation Intercalation to Heal Inorganic CsPbI Perovskite.

The in situ formation of reduced dimensional perovskite layer via post-synthesis ion exchange has been an effective way of passivating organic-inorganic hybrid perovskites. In contrast, cesium ions in Cs-based inorganic perovskite with strong ionic binding energy cannot exchange with those well-known organic cations to form reduced dimensional perovskite. Herein, we demonstrate that tetrabutylammonium (TBA ) cation can intercalate into CsPbI to effectively substitute the Cs cation and to form one-dimensional (1D) TBAPbI layer in the post-synthesis TBAI treatment.

Chemically Stable Black Phase CsPbI Inorganic Perovskites for High-Efficiency Photovoltaics.

Research on chemically stable inorganic perovskites has achieved rapid progress in terms of high efficiency exceeding 19% and high thermal stabilities, making it one of the most promising candidates for thermodynamically stable and high-efficiency perovskite solar cells. Among those inorganic perovskites, CsPbI with good chemical components stability possesses the suitable bandgap (≈1.7 eV) for single-junction and tandem solar cells.

5-Ammonium Valeric Acid Iodide to Stabilize MAPbI via a Mixed-Cation Perovskite with Reduced Dimension.

5-Ammonium valeric acid iodide (AVAI) has been widely known as a stabilizer to enhance the stability of MAPbI perovskite, but its role and function is still under exploration. The typical 2D perovskites of AVAPbI have been proposed as the capping layer for stabilization. Here, a novel AVA-MA mixed-cation perovskite of AVAMAPbI is found to show a more even and compact coverage than the typical 2D perovskite of AVAPbI.