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1. High‐Performance Perovskite Photovoltaics by Heterovalent Substituted Mixed Perovskites

   https://doi.org/10.1002/adfm.202207911  

   Shen, Lening ; Chen, Rui ; Zhang, Dong ; Yilmazoglu, Unal Cagatay ; Gu, Kai ; Sarmiento, Julio S. ; Zhu, Tao ; Zheng, Luyao ; Zheng, Jie ; Wang, He ; et al ( September 2022 , Advanced Functional Materials)

   2D perovskites are relatively stable but possess poor charge transport compared to 3D perovskites. To boost charge transport, novel 2D perovskites mixed with 3D perovskites are developed, where Pb²⁺are partially substituted by the heterovalent neodymium cations (Nd³⁺) within both 2D and 3D perovskites (termed Nd³⁺‐substituted 2D:3D mixed perovskites. Systematical studies reveal that the Nd³⁺‐substituted 2D:3D mixed perovskites possess larger crystals, superior crystallinity, suppressed non‐radiative charge recombination, and enhanced and balanced charge transport compared to the 2D:3D mixed perovskites. As a result, perovskite photovoltaics based on the Nd³⁺‐substituted 2D:3D mixed perovskites exhibit a power conversion efficiency of 22.11%, a photoresponsibility of over 700 mA W⁻¹, a photodetectivity of 4.29 × 10¹⁴ cm Hz^1/2 W⁻¹, a linear dynamic range of 165 dB at room temperature, and dramatically boosted stability. These results demonstrate that, a facile way is developed to realize high‐performance perovskite photovoltaics through partially heterovalent substituted Pb²⁺by Nd³⁺within 2D:3D mixed perovskites.

    

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2. Two‐Dimensional Organic–Inorganic Hybrid Perovskites: A New Platform for Optoelectronic Applications

   https://doi.org/10.1002/adma.201802041  

   Hu, Jun ; Yan, Liang ; You, Wei ( September 2018 , Advanced Materials)

   2D perovskites are recently attracting a significant amount of attention, mainly due to their improved stability compared with their 3D counterpart, e.g., the archetypical MAPbI₃. Interestingly, the first studies on 2D perovskites can be dated back to the 1980s. The most popular 2D perovskites have a general formula of (RNH₃)₂MA_n−1M_nX_3n+1, wherenrepresents the number of metal halide octahedrons between the insulating organic cation layers. The optoelectronic properties of 2D perovskites, e.g., band gap, are highly dependent on the thickness of the inorganic layers (i.e., the value ofn). Herein, 2D perovskites are arbitrarily divided into three classes, strict 2D (n= 1), quasi‐2D (n= 2–5), and quasi‐3D (n> 5), and research progress is summarized following this classification. The majority of existing 2D perovskites only employ very simple organic cations (e.g., butyl ammonium or phenylethyl ammonium), which merely function as the supporting layer/insulating barrier to achieve the 2D structure. Thus, a particularly important research question is: can functional organic cations be designed for these 2D perovskites, where these functional organic cations would play an important role in dictating the optoelectronic properties of these organic–inorganic hybrid materials, leading to unique device performance or applications?

    

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3. High‐Efficiency Quasi‐2D Perovskite Solar Cells Incorporating 2,2′‐Biimidazolium Cation

   https://doi.org/10.1002/solr.202000700  

   Fu, Weifei ; Zhao, Ting ; Liu, Hongbin ; Lin, Francis ; Zuo, Lijian ; Li, Xiaosong ; Jen, Alex K. -Y. ( February 2021 , Solar RRL)

   Quasi‐2D perovskites are attractive because of their improved stability compared with 3D perovskites counterparts; however, they suffer from poor performance due to the insulating organic cation spacers. To resolve this issue, a strategy of replacing the insulating spacer with conducting spacer is proposed which successfully converts the spacer from a charge‐transporting “barrier” to charge‐transporting “bridge.” Specifically, an alkyl linker‐free, fully conjugated aromatic 2,2′‐biimidazolium (BIDZ) cation is introduced as a spacer to compose quasi‐2D perovskites. Density functional theory (DFT) simulation results show that the lowest unoccupied molecular orbital (LUMO) level localizes on BIDZ and the highest occupied molecular orbital (HOMO) level is on the perovskite. However, both HOMO and LUMO levels localize on perovskite slabs for the well‐known phenethylammonium (PEA)‐based 2D perovskites. The strong electronic coupling between BIDZ and 3D perovskite slabs improves carrier mobilities even for a low‐weak‐crystallinity and random‐orientated quasi‐2D perovskite film. As a result, a remarkable power conversion efficiency up to 11.4% (n = 5) is achieved, which is much higher than that of PEA‐based random‐orientated quasi‐2D perovskites with the same processing condition (6.5%). The strategy paves the way to highly efficient and stable quasi‐2D perovskites solar cells through designing new organic spacer cations.

    

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4. Merits and Challenges of Ruddlesden–Popper Soft Halide Perovskites in Electro‐Optics and Optoelectronics

   https://doi.org/10.1002/adma.201803514  

   Chen, Zhizhong ; Guo, Yuwei ; Wertz, Esther ; Shi, Jian ( October 2018 , Advanced Materials)

   Following the rejuvenation of 3D organic–inorganic hybrid perovskites, like CH₃NH₃PbI₃, (quasi)‐2D Ruddlesden–Popper soft halide perovskites R₂A_n−1Pb_nX_3n+1have recently become another focus in the optoelectronic and photovoltaic device community. Although quasi‐2D perovskites were first introduced to stabilize optoelectronic/photovoltaic devices against moisture, more interesting properties and device applications, such as solar cells, light‐emitting diodes, white‐light emitters, lasers, and polaritonic emission, have followed. While delicate engineering design has pushed the performance of various devices forward remarkably, understanding of the fundamental properties, especially the charge‐transfer process, electron–phonon interactions, and the growth mechanism in (quasi)‐2D halide perovskites, remains limited and even controversial. Here, after reviewing the current understanding and the nexus between optoelectronic/photovoltaic properties of 2D and 3D halide perovskites, the growth mechanisms, charge‐transfer processes, vibrational properties, and electron–phonon interactions of soft halide perovskites, mainly in quasi‐2D systems, are discussed. It is suggested that single‐crystal‐based studies are needed to deepen the understanding of the aforementioned fundamental properties, and will eventually contribute to device performance.

    

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5. Self-powered photodetectors based on Ruddlesden–Popper 2D hybrid perovskites with carbazole derivatives

   https://doi.org/10.1063/5.0179297  

   Alphenaar, Anna Niamh ; Zhang, Xiaoyu ; Xu, Yuanze ; Ramakrishnan, Shripathi ; Zhang, Yugang ; Yu, Qiuming ( December 2023 , Applied Physics Letters)

   Recently, carbazole-based organic cations have garnered interest for their potential application in two-dimensional (2D) layered hybrid perovskite solar cells because of their strong hole extraction and transport as well as humidity resistance. However, the potential incorporation of carbazole-based Ruddlesden–Popper 2D hybrid perovskites in photodetectors has been largely unexplored. In this study, we synthesized ammonium 1-(9H-carbazol-9-yl) ethanaminium iodide (CzEAI) and fabricated (CzEA)2PbI4 2D perovskite thin films via varying solvent conditions to control film morphology. We constructed photodiode-type photodetectors with the active layer of (CzEA)2PbI4 2D perovskites and demonstrated a specific detectivity of 6.95 × 1010 Jones at 485 nm illumination without external bias. These results demonstrate the potential of carbazole-based 2D perovskites in a wide range of optoelectronic applications.

    

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