Mahui

Coherent spin dynamics of electrons and holes in CsPbBr₃ perovskite crystals

Coherent spin dynamics of electrons and holes in CsPbBr₃ perovskite crystals, Published online: 08 February 2019; doi:10.1038/s41467-019-08625-z

Cation-swapped homogeneous nanoparticles in perovskite oxides for high power density

Cation-swapped homogeneous nanoparticles in perovskite oxides for high power density, Published online: 11 February 2019; doi:10.1038/s41467-019-08624-0

e_g occupancy as an effective descriptor for the catalytic activity of perovskite oxide-based peroxidase mimics

<i>e</i>_g occupancy as an effective descriptor for the catalytic activity of perovskite oxide-based peroxidase mimics, Published online: 11 February 2019; doi:10.1038/s41467-019-08657-5

A highly transparent nickel oxide hole transport layers prepared by oxygen‐assisted electron beam evaporation for perovskite‐based photovoltaics is reported. Using these layers in perovskite solar cells, efficient devices with stable power conversion efficiencies up to 18.5% for inkjet‐printed absorbers and 15.4% for co‐evaporated absorbers are demonstrated. In addition, good stability at elevated temperature and under ultraviolet radiation is shown.

Abstract

High‐quality charge carrier transport materials are of key importance for stable and efficient perovskite‐based photovoltaics. This work reports on electron‐beam‐evaporated nickel oxide (NiO _x ) layers, resulting in stable power conversion efficiencies (PCEs) of up to 18.5% when integrated into solar cells employing inkjet‐printed perovskite absorbers. By adding oxygen as a process gas and optimizing the layer thickness, transparent and efficient NiO _x hole transport layers (HTLs) are fabricated, exhibiting an average absorptance of only 1%. The versatility of the material is demonstrated for different absorber compositions and deposition techniques. As another highlight of this work, all‐evaporated perovskite solar cells employing an inorganic NiO _x HTL are presented, achieving stable PCEs of up to 15.4%. Along with good PCEs, devices with electron‐beam‐evaporated NiO _x show improved stability under realistic operating conditions with negligible degradation after 40 h of maximum power point tracking at 75 °C. Additionally, a strong improvement in device stability under ultraviolet radiation is found if compared to conventional perovskite solar cell architectures employing other metal oxide charge transport layers (e.g., titanium dioxide). Finally, an all‐evaporated perovskite solar mini‐module with a NiO _x HTL is presented, reaching a PCE of 12.4% on an active device area of 2.3 cm².

Fluorinated aromatic cations (FPEAI) can react with the excess PbI₂ in a 3D perovskite film to form a capping 2D perovskite layer. Compared to the control device, the resulting multidimensional perovskite shows enhanced environmental stability with equally superior device performances. Judicious optimization of the perovskite precursor recipe realizes a power conversion efficiency of 20.54% for mesoporous perovskite solar cells.

Abstract

Supported by the density functional theory (DFT) calculations, for the first time, a fluorinated aromatic cation, 2‐(4‐fluorophenyl)ethyl ammonium iodide (FPEAI), is introduced to grow in situ a low dimensional perovskite layer atop 3D perovskite film with excess PbI₂. The resulted (p‐FC₆H₄C₂H₄NH₃)₂[PbI₄] perovskite functions as a protective capping layer to protect the 3D perovskite from moisture. In the meantime, the thin layer facilitates charge transfer at the interfaces, thereby reducing the nonradiative recombination pathways. Laser scanning confocal microscopy unveils visually the distribution of the 2D perovskite layer on top of the 3D perovskite. When employing the 3D–2D perovskite as the absorbing layer in the photovoltaic cells, a high power conversion efficiency of 20.54% is realized. Superior device performance and moisture stability are observed with the modified perovskite over the whole stability test period.

The photophysics and nature of localized traps and their role on the optical properties of lead bromide perovskite films are investigated using optical spectroscopy and theoretical modeling. A clear understanding of the origin and nature of localized traps has important ramifications for perovskite light harvesting and emitting applications, as well as the design of new perovskites.

Abstract

Traps exert an omnipotent influence over the performance of halide perovskite optoelectronic devices. A clear understanding of the origin and nature of the traps in halide perovskites is the key to controlling them and realizing optimal devices. Herein, the role of localized traps on the optical properties of lead bromide perovskite films is investigated. In the low‐temperature orthorhombic phase of CH₃NH₃PbBr₃ perovskite, band‐edge carrier dynamics exhibit a power‐law decay due to the presence of structural‐disorder‐induced localized traps, which has a depth of ≈40 meV. The continuous distribution of these localized traps gives rise to a broad sub‐band‐gap emission that becomes more prominent in thicker films with a larger trap density. The presence of this emission only from the hybrid organic–inorganic perovskites points to the vital role of organic dipoles in localized trap states formation. This study explicates the nature of these localized traps as well as their nontrivial role in carrier recombination kinetics, which is of fundamental importance in perovskites optoelectronics.

One of the problems that restrict the further development of perovskite solar cells (PSCs) is hysteresis, making it difficult to evaluate the reliable performance of PSCs. Recent process regarding the strategies to efficiently reduce hysteresis in PSCs is reviewed. The influential factors and possible reasons are also outlined.

Abstract

Organic–inorganic hybrid perovskite solar cells (PSCs) have become a promising candidate in the photovoltaic field due to their high power conversion efficiency and low material cost. However, the development of PSCs is limited by their poor stability under practical conditions in the presence of oxygen, moisture, sunlight, heat, and the current–voltage (I–V) hysteresis. In particular, the hysteretic I–V issue casts doubt on the validity of the photovoltaic performance results that are achieved, making it difficult to evaluate the authentic performance of PSCs. This review article focuses on understanding the I–V hysteresis behavior in PSCs and on exploring the possible reasons leading to this hysteresis phenomenon. The various strategies attempted to suppress the I–V hysteresis in PSCs are summarized, and a brief future recommendation is provided.

Halide double perovskites represent a promising direction to fabricate lead‐free optoelectronic devices. The current progress and setbacks in crystal structures, materials preparation, optoelectronic properties, stability, challenge, and photovoltaic applications of lead‐free halide double perovskite compounds are reviewed in detail.

Abstract

The field of halide metal perovskite photovoltaics has caught widespread interest in the last decade. This is seen in the rapid rise of power conversion efficiency, which is currently over 23%. It has also stimulated a widespread application of halide metal perovskites in other fields, such as light‐emitting diodes, field‐effect transistors, detectors, and lasers. Despite the fascinating characteristics of the halide metal perovskites, the presence of toxic lead (Pb) in their chemical composition is regarded as one of the major limiting factors preventing their commercialization. Addressing the toxicity issues in these compounds by a careful and strategic replacement of Pb²⁺ with other nontoxic candidate elements represents a promising direction to fabricate lead‐free optoelectronic devices. Such attempts yield a halide double perovskite structure which allows flexibility for various compositional adjustments. Here, the authors present the current progress and setbacks in crystal structures, materials preparation, optoelectronic properties, stability, and photovoltaic applications of lead‐free halide double perovskite compounds. Prospective research directions to improve the optoelectronic properties of existing materials are given that may help in the discovery of new lead‐free halide double perovskites.