Over the past few years, lead‐halide perovskites (LHPs), both in the form of bulk thin films and colloidal nanocrystals (NCs), have revolutionized the field of optoelectronics, emerging at the forefront of next‐generation optoelectronics. The power conversion efficiency (PCE) of halide perovskite solar cells has increased from 3.8% to over 25.7% over a short period of time and is very close to the theoretical limit (33.7%). At the same time, the external quantum efficiency (EQE) of perovskite LEDs has surpassed 23% and 20% for green and red emitters, respectively. Despite great progress in device efficiencies, the photoactive phase instability of perovskites is one of the major concerns for the long‐term stability of the devices and is limiting their transition to commercialization. In this regard, researchers have found that the phase stability of LHPs and the reproducibility of the device performance can be improved by A‐site cation alloying with two or more species, these are named mixed cation (double, triple, or quadruple) perovskites. This review provides a state‐of‐the‐art overview of different types of mixed A‐site cation bulk perovskite thin films and colloidal NCs reported in the literature, along with a discussion of their synthesis, properties, and progress in solar cells and LEDs.

https://www.investigo.biblioteca.uvigo.es/xmlui/bitstream/11093/3875/3/2022_byranvand_mixed_asite_cation.pdf

Recent Progress in Mixed A‐Site Cation Halide Perovskite Thin‐Films and Nanocrystals for Solar Cells and Light‐Emitting Diodes

The spectral instability issue is a challenge in blue perovskite light-emitting diodes (PeLEDs). Dion-Jacobson (DJ) phase perovskites are promising alternatives to achieve high-quality blue PeLEDs. However, the current exploration of DJ phase perovskites is focused on symmetric divalent cations, and the corresponding efficiency of blue PeLEDs is still inferior to that of green and red ones. In this work, we report a new type of DJ phase CsPb(Br/Cl)3 perovskite via introduction of an asymmetric molecular configuration as the organic spacer cation in perovskites. The primary and tertiary ammonium groups on the asymmetric cations bridge with the lead halide octahedra forming the DJ phase structures. Stable photoluminescence spectra were demonstrated in perovskite films owing to the suppressed halide segregation. Meanwhile, the radiative recombination efficiency of charges is improved significantly as a result of the confinement effects and passivation of charge traps. Finally, we achieved an external quantum efficiency of 2.65% in blue PeLEDs with stable spectra emission under applied bias voltages. To our best knowledge, this is the first report of asymmetric cations used in PeLEDs, which provides a facile solution to the halide segregation issue in PeLEDs.

Spectral Stable Blue-Light-Emitting Diodes via Asymmetric Organic Diamine Based Dion-Jacobson Perovskites.

Over the last decade, lead halide perovskites have attracted significant research attention in the field of photovoltaics, light-emitting devices, photodetection, ionizing radiation detection, etc, owing to their outstanding optoelectrical properties. However, the commercial applications of lead-based perovskite devices are restricted due to the poor ambient stability and toxicity of lead. The encapsulation of lead-based devices can reduce the possible leakage of lead. However, it is hard to ensure safety during large-scale production and long-term storage. Recently, considerable efforts have been made to design lead-free perovskites for different optoelectronic applications. Metal halide double perovskites with the general formula of A2MIMIIIX6 or A2MIVX6 could be potentially considered as green and stable alternatives for different optoelectronic applications. In this review article, we focus on the recent progress and findings on lead-free halide double perovskites for x-ray and UV–vis photodetection applications. Lead-free halide double perovskite has recently drawn a great deal of attention for superior x-ray detection due to its high absorption coefficient, large carrier mobility-lifetime product, and large bulk resistance. In addition, these materials exhibit good performance in photodetection in the UV–vis region due to high photocarrier generation and efficient carrier separation. In this review, first, we define the characteristics of lead-free double perovskite materials. The fundamental characteristics and beneficial properties of halide perovskites for direct and indirect x-ray detection are then discussed. We comprehensively review recent developments and efforts on lead-free double perovskite for x-ray detection and UV–vis photodetection. We bring out the current challenges and opportunities in the field and finally present the future outlook for developing lead-free double perovskite-based x-ray and UV–vis photodetectors for practical applications.

Recent advances in lead-free double perovskites for x-ray and photodetection

High-efficient yellow-green emission in (TDMP)MnBr4 single crystal with modulation of spin-phonon-charge interactions

Metal halide perovskites (MHPs) have attracted extensive attention due to their excellent optoelectronic properties. Among them, layered two-dimensional (2D) metal halide materials with special structures have attracted extensive attention due to their superior stability and optoelectronic properties. Here, we report the 2D Ruddlesden–Popper (RP) phase Cs3Cd2Cl7 synthesized by a solvothermal method, and the photoluminescence quantum yields (PLQYs) of the pristine Cs3Cd2Cl7 sample (PLQY ∼ 10%) can be increased to 68 ± 5% through appropriate Sb3+ doping. This should be the highest PLQY of all reported all-inorganic RP-phase Cd-based perovskites so far. Our results indicate that the highly efficient cyan emission can be attributed to the common self-trapped exciton (STE) emission of the triplet states of Cd2+ and Sb3+ induced by strong electron–phonon coupling, and Sb3+:Cs3Cd2Cl7 has excellent structural and spectral stability. This new material should be a promising candidate for optoelectronic applications in the future. 

Efficient Self-Trapped Exciton Emission in Ruddlesden–Popper Sb-Doped Cs3Cd2Cl7 Perovskites

Two-dimensional (2D) perovskites are known as one of the most promising luminescent materials due to their structural diversity and outstanding optoelectronic properties. Compared with 3D perovskites, 2D perovskites have natural quantum well structures, large exciton binding energy (Eb) and outstanding thermal stability, which shows great potential in the next-generation displays and solid-state lighting. In this review, the fundamental structure, photophysical and electrical properties of 2D perovskite films were illustrated systematically. Based on the advantages of 2D perovskites, such as special energy funnel process, ultra-fast energy transfer, dense film and low efficiency roll-off, the remarkable achievements of 2D perovskite light-emitting diodes (PeLEDs) are summarized, and exciting challenges of 2D perovskite are also discussed. An outlook on further improving the efficiency of pure-blue PeLEDs, enhancing the operational stability of PeLEDs and reducing the toxicity to push this field forward was also provided. This review provides an overview of the recent developments of 2D perovskite materials and LED applications, and outlining challenges for achieving the high-performance devices.

/pdf/advances-and-challenges-in-two-dimensional-organic-inorganic-1024ne73gn.pdf

Miao Ren

Papers

Advances and Challenges in Two-Dimensional Organic-Inorganic Hybrid Perovskites Toward High-Performance Light-Emitting Diodes