Low-Dimensional-Networked Perovskites with A-Site-Cation Engineering for Optoelectronic Devices

Extendable Synthesis of Organic Cations for In Situ Construction of Hybrid Metal Halides with Near-Unity Photoluminescence and Strong Second Harmonic Generation

The A-site organic components of organic-inorganic hybrid metal halides (OIHMHs) significantly impact their crystal structure and optoelectronic properties. However, chemical modification of A-site cations has been mostly limited to commercial organic precursors, which restricts the structural variability of OIHMHs for optimal functionalities. Herein we have proposed an extendable synthesis approach to the direct procurability of various organic cations with desireable structures for the in situ construction of a library of OIHMH materials. The template condensation reaction between dimethyl sulfoxide and acetone derivatives yields A-site organic cations with exquisite control of modularization and regioselectivity within the OIHMH crystallization system. The as-fabricated OIHMHs demonstrated highly efficient linear optical photoluminescence or nonlinear optical second harmonic generation, promising potential applications in photonic devices. This in situ synthetic strategy offers a structural extension of OIHMHs and establishes a fundamental methodological platform for screening functional OIHMH materials.

Interface Engineering of Substrate-Integrated Single-Crystal Perovskite Wafers for Sensitive X-Ray Detection

Metal halide perovskite single crystals are emerging candidates for X-ray detection, however, it is challenging for growth of thickness-controlled single-crystal wafer on commercial backplanes, limiting their practical imaging application. Herein, integration of micrometer-thick methylammonium lead triiodide (MAPbI3) single-crystal wafer on indium tin oxide (ITO) substrates by methylamine (MA)-induced interface recrystallization is reported. Through selection of hole transport material with rich functional group, intimate interface contact with low trap density can be achieved, leading to superior carrier transport properties and homogeneous photoresponse. The as-fabricated X-ray detectors exhibit high sensitivity of 1.4 × 104 µC Gyair -1 cm-2 and low detection limit of 177 nGyair s-1, which are comparable to previous reports based on free-standing MAPbI3 bulk crystals. This work provides a feasible strategy for constructing substrate-integrated single-crystal perovskite wafers with controlled thickness, which may promote practical imaging application of perovskite X-ray detectors.

Dark Current in Broadband Perovskite-Organic Heterojunction Photodetectors Controlled by Interfacial Energy Band Offset

Lead halide perovskite and organic semiconductors are promising classes of materials for photodetector (PD) applications. State-of-the-art perovskite PDs have performance metrics exceeding silicon PDs in the visible. While organic semiconductors offer bandgap tunability due to their chemical design with detection extended into the near-infrared (NIR), perovskites are limited to the visible band and the first fraction of the NIR spectrum. In this work, perovskite-organic heterojunction (POH) PDs with absorption up to 950 nm are designed by the dual contribution of perovskite and the donor:acceptor bulk-heterojunction (BHJ), without any intermediate layer. The effect of the energetics of the donor materials is systematically studied on the dark current (Jd) of the device by using the PBDB-T polymer family. Combining the experimental results with drift-diffusion simulations, it is shown that Jd in POH devices is limited by thermal generation via deep trap states in the BHJ. Thus, the best performance is obtained for the PM7-based POH, which delivers an ultra-low noise current of 2 × 10-14 A Hz-1/2 and high specific detectivity of 4.7 × 1012 Jones in the NIR. Last, the application of the PM7-based POH devices as NIR pulse oximeter with high-accuracy heartbeat monitoring at long-distance of 2 meters is demonstrated.

Dimensionality Engineering of Organic-Inorganic Halide Perovskites for Next-Generation X-Ray Detector

The next-generation X-ray detectors require novel semiconductors with low material/fabrication cost, excellent X-ray response characteristics, and robust operational stability. The family of organic-inorganic hybrid perovskites (OIHPs) materials comprises a range of crystal configuration (i.e., films, wafers, and single crystals) with tunable chemical composition, structures, and electronic properties, which can perfectly meet the multiple-stringent requirements of high-energy radiation detection, making them emerging as the cutting-edge candidate for next-generation X-ray detectors. From the perspective of molecular dimensionality, the physicochemical and optoelectronic characteristics of OIHPs exhibit dimensionality-dependent behavior, and thus the structural dimensionality is recognized as the key factor that determines the device performance of OIHPs-based X-ray detectors. Nevertheless, the correlation between dimensionality of OIHPs and performance of their X-ray detectors is still short of theoretical guidance, which become a bottleneck that impedes the development of efficient X-ray detectors. In the review, the advanced studies on the dimensionality engineering of OIHPs are critically assessed in X-ray detection application, discussing the current understanding on the "dimensionality-property" relationship of OIHPs and the state-of-the-art progresses on the dimensionality-engineered OIHPs-based X-ray detector, and highlight the open challenges and future outlook of this field.

Alkylammonium Halides for Phase Regulation and Luminescence Modulation of Cesium Copper Iodide Nanocrystals for Light-Emitting Diodes

All-inorganic cesium copper halide nanocrystals have attracted extensive attention due to their cost-effectiveness, low toxicity, and rich luminescence properties. However, controlling the synthesis of these nanocrystals to achieve a precise composition and high luminous efficiency remains a challenge that limits their future application. Herein, we report the effect of oleylammonium iodide on the synthesis of copper halide nanocrystals to control the composition and phase and modulate their photoluminescence (PL) quantum yields (QYs). For CsCu2I3, the PL peak is centered at 560 nm with a PLQY of 47.3%, while the PL peak of Cs3Cu2I5 is located at 440 nm with an unprecedently high PLQY of 95.3%. Furthermore, the intermediate-state CsCu2I3/Cs3Cu2I5 heterostructure shows white light emission with a PLQY of 66.4%, chromaticity coordinates of (0.3176, 0.3306), a high color rendering index (CRI) of 90, and a correlated color temperature (CCT) of 6234 K, indicating that it is promising for single-component white-light-emitting applications. The nanocrystals reported in this study have excellent luminescence properties, low toxicity, and superior stability, so they are more suitable for future light-emitting applications.

2D Ruddlesden-Popper Sn-Based Perovskite Weak Light Detector for Image Transmission and Reflection Imaging

2D Ruddlesden-Popper Sn-based perovskite has excellent optoelectronic properties and weak halide ion migration characteristics, making it an ideal candidate for weak light detection, which has great potential in light communication, and medical applications. Although Sn-based perovskite photodetectors are developed, weak light detection is not demonstrated yet. Herein, a high-performance self-powered photodetector with the capability to detect ultra-weak light signals is designed based on vertical PEA2 SnI4 /Si nanowires heterojunction. Due to the low dark current and high light absorption efficiency, the devices present a remarkable responsivity of 42.4 mA W-1 , a high detectivity of 8 × 1011 Jones, and an ultralow noise current of 2.47 × 10-13 A Hz-1/2 . Especially, the device exhibits a high on-off current ratio of 18.6 at light signals as low as 4.60 nW cm-2 , revealing the capacity to detect ultra-weak light. The device is applied as a signal receiver and realized image transmission in light communication system. Moreover, high-resolution reflection imaging and multispectral imaging are obtained using the device as the sensor in the imaging system. These results reveal that 2D PEA2 SnI4 -based self-powered photodetectors with low-noise current possess enormous potential in future weak light detection.

Long-chain organic molecules enable mixed dimensional perovskite photovoltaics: a brief view

The remarkable optoelectronic properties of organometal halide perovskite solar cells have captivated significant attention in the energy sector. Nevertheless, the instability of 3D perovskites, despite their extensive study and attainment of high-power conversion efficiency, remains a substantial obstacle in advancing PSCs for practical applications and eventual commercialization. To tackle this issue, researchers have devised mixed-dimensional perovskite structures combining 1D and 3D components. This innovative approach entails incorporating stable 1D perovskites into 3D perovskite matrices, yielding a significant improvement in long-term stability against various challenges, including moisture, continuous illumination, and thermal stress. Notably, the incorporation of 1D perovskite yields a multitude of advantages. Firstly, it efficiently passivates defects, thereby improving the overall device quality. Secondly, it retards ion migration, a pivotal factor in degradation, thus further bolstering stability. Lastly, the inclusion of 1D perovskite facilitates charge transport, ultimately resulting in an elevated device efficiency. In this succinct review, we thoroughly encapsulate the recent progress in PSCs utilizing 1D/3D mixed-dimensional architectures. These advancements encompass both stacked bilayer configurations of 1D/3D structures and mixed monolayer structures of 1D/3D. Additionally, we tackle critical challenges that must be surmounted and offer insights into the prospects for further advancements in this domain.

Introducing Ferroelasticity into 1D Hybrid Lead Halide Semiconductor by Halogen Substitution Strategy

Organic-inorganic hybrid lead halide perovskites (OLHPs), represented by (CH3 NH3 )PbI3 , are one of the research focus due to their exceptional performance in optoelectronic applications, and ferroelastic domain walls are benign to their charge carrier transport that is confirmed recently. Among them, the 1D OLHPs feature better stability against desorption and moisture, but related 1D ones possessing ferroelasticity are rarely investigated and reported so far. In this work, the 1D ferroelastic semiconductor (N-iodomethyl-N-methyl-morpholinium)PbI3 ((IDMML)PbI3 ) is prepared successfully by introducing successively halogenate atoms from Cl, Br to I into the organic cation of the prototype (N,N-dimethylmorpholinium)PbI3 ((DMML)PbI3 ). Notably, (IDMML)PbI3 shows the narrow bandgap energy (≈2.34 eV) according to the ultraviolet-visible absorption spectrum and the theoretical calculation, and possesses the evident photoconductive characteristic with the on/off ratio of current of ≈50 under the 405 nm light irradiation. This work provides a new case for the ferroelastic OLHPs and will inspire intriguing research in the field of optoelectronic.

Collaborative Passivation for Dual Charge Transporting Layers Based on 4-(chloromethyl)benzonitrile Additive toward Efficient and Stable Inverted Perovskite Solar Cells

Poor carrier transport capacity and numerous surface defects of charge transporting layers (CTLs), coupled with misalignment of energy levels between perovskites and CTLs, impact photoelectric conversion efficiency (PCE) of inverted perovskite solar cells (PSCs) profoundly. Herein, a collaborative passivation strategy is proposed based on 4-(chloromethyl) benzonitrile (CBN) as a solution additive for fabrication of both [6,6]-phenyl-C61-butyric acid methylester (PCBM) and poly(triarylamine) (PTAA) CTLs. This additive can improve wettability of PTAA and reduce the agglomeration of PCBM particles, which enhance the PCE and device stability of the PSCs. As a result, a PCE exceeding 20% with a remarkable short circuit current of 23.9 mA cm^-2 , and an improved fill factor of 81% is obtained for the CBN- modified inverted PSCs. Devices maintain 80% and 70% of the initial PCE after storage under 30% and 85% humidity ambient conditions for 1000 h without encapsulation, as well as negligible light state PCE loss. This strategy demonstrates feasibility of the additive engineering to improve interfacial contact between the CTLs and perovskites for fabrication of efficient and stable inverted PSCs.

Hybrid 2D perovskite and red emitting carbon dot composite for improved stability and efficiency of LEDs

Organic-inorganic hybrid lead trihalide perovskites have shown promise consistently in optoelectronic devices such as light-emitting diodes (LEDs), solar cells, photodetectors, sensors, and other optoelectronic devices. Perovskite-based LEDs (PSK-LEDs) have shown enormous potential, mostly due to their lower cost, easy synthesis via solution processibility, and highly tunable light-emitting behavior with higher performance. Despite the recent developments in green and blue PSK-LEDs over the years, there has been less development in the research area of red-emitting PSK-LEDs. Although some developments have led to spectrally, stable red-emitting PSK-LEDs, the stability of those devices still needs to be improved upon further for any practical application. In this work, to the best of our knowledge, for the first time, we used red-emitting 2D PSK as an active light-emitting layer which was further stabilized by red-emitting carbon dots (CDs). The CD-PSK composite films were used as an active layer in red emitting LEDs, and they showed high operational stability, and improved performance compared to the control device with only PSK film as the active layer. The composite device showed improved maximum luminescence (3011 cd m-2), charge density (330 mA cm-2), operational stability (8 hours), better EQE (10.2%), and low turn-on voltage of 2.6 V compared to the control device with maximum luminescence (1512 cd m-2), charge density (134 mA cm-2), operational stability (<2 hours), EQE (2.6%) and turn on voltage of 3.2 V. The low-cost hybrid approach using PSK building blocks together with CDs opens a new approach leading to a composite material, which has immense possibilities for tuning the structure further to maximize the performance.

Multidimensional perovskite solar cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted extensive attention, and their certified power conversion efficiency (PCE) has reached 25.5%. However, the instability of the high-efficiency 3-dimensional (3D) perovskite against ambient conditions (moisture, light and thermal) and the existing defects severely limit its practical applications and commercialization. Unlike 3D perovskites, the large hydrophobic spacer cations in low-dimensional (2D, 1D, and 0D) perovskites are able to effectively improve the stability, but they also weaken the light absorption range and hinder charge transport. The construction of a low-dimensional/3D perovskite multidimensional structure, which can combine the advantages of the high stability of low-dimensional perovskites and the superior efficiency of 3D perovskites, is proposed to achieve high efficiency and ultrastability. Moreover, the proper incorporation of low-dimensional perovskite into 3D perovskite can passivate defects and inhibit ion migration. Herein, this article summarizes the recent research progress of low-dimensional/3D perovskite multidimensional structures for PSCs and provides some perspectives toward developing stable and efficient PSCs.

Hetero-perovskite engineering for stable and efficient perovskite solar cells

This review summarizes and discusses the HPSC engineering and optimization mechanism, and provides systematic knowledge and prospects of their development in the photovoltaic field.

In Situ Perovskitoid Engineering at SnO2 Interface toward Highly Efficient and Stable Formamidinium Lead Triiodide Perovskite Solar Cells

The black-phase formamidinium lead triiodide (α-FAPbI₃) perovskite has turned out to be one of the most efficient light harvesting materials. However, the phase stability of FAPbI₃ is a long-standing issue. Herein, we introduce a layer of tetrabutylammonium fluoride (TBAF) on SnO₂, which would form an in situ layer of TBAPbI₃ perovskitoid at the SnO₂/FAPbI₃ interface by interacting with PbI₂. The results show that this strategy could improve the conductivity of SnO₂, passivate the defects in perovskite, improve the phase stability of α-FAPbI₃, and retard the nonradiative recombination in the device. As a result, we obtain a champion device with a power conversion efficiency of 23.1% under AM 1.5 G illumination of 100 mW/cm². The unencapsulated devices can maintain excellent stability under illumination, thermal stress, and humidity conditions, respectively.

Solvent-assisted crystallization of two-dimensional Ruddlesden-Popper perovskite

Two dimensional (2D) perovskite materials, are more stable than 3D perovskite materials, which could solve the stability issue of perovskite solar cells (PSCs). However, the photovoltaic conversion efficiency (PCE) of PSCs based on 2D perovskite materials was low, due to the high dielectric and quantum confinement of 2D perovskite. In this work, we propose a solvent-assisted method to prepare 2D perovskite films, where the solvent was distributed in a gradient. Therefore, the top-down crystallization process of 2D perovskite can be accurately controlled. The PCE of PSCs fabricated by the solvent-assisted method was enhanced by 48%, compared with the control device. For the packaged devices, the stability test demonstrated that 94% of the initial PCE was still maintained after 1500 hours of storage (25 °C, RH 40%). After carefully analyzing the photophysical process of the carriers in the PSCs based on 2D perovskite, the enhanced carrier transfer mechanism of the solvent-assisted method has been proposed.