High-quality Perovskite Research Articles

Highly ordered crystallization of α-FAPbI3 films via homogeneous seeds for efficient perovskite solar cells

Formamidine lead triiodide (FAPbI3) perovskites have become the most promising photovoltaic materials for perovskite solar cells with record power conversion efficiency (PCE). However, random nucleation, phase transition, and lattice defects are still the key challenges limiting the quality of FAPbI3 films. Previous studies show that the introduction or adding of seeds in the precursor is effective to promote the nucleation and crystallization of perovskite films. Nevertheless, the seed-assisted approach focuses on heterogeneous seeds or hetero-composites, which inevitably induce a lattice-mismatch, the generation of strain or defects, and the phase segregation in the perovskite films. Herein, we first demonstrate that high-quality perovskite films are controllably prepared using α- and δ-phases mixed FAPbI3 microcrystal as the homogeneous seeds with the one-step antisolvent method. The partially dissolved seeds with suitable sizes improve the crystallinity of the perovskite film with preferable orientation, improved carrier lifetime, and increased carrier mobility. More importantly, the α-phase-containing seeds promote the formation of α-phase FAPbI3 films, leading to the reduction of residual lattice strain and the suppression of I− ion migration. Besides, the adding of dimethyl 2,6-pyridine dicarboxylate (DPD) into the precursor further suppresses the generation of defects, contributing to the PCE of devices prepared in air ambient being significantly improved to 23.75%, among the highest PCEs for fully air-processed FAPbI3 solar cells. The unpackaged target devices possess a high stability, maintaining 80% of the initial PCE under simulated solar illumination exceeding 800 h.

Dipolar Chemical Bridge Induced CsPbI3 Perovskite Solar Cells with 21.86 % Efficiency.

CsPbI3 perovskite receives tremendous attention for photovoltaic applications due to its ideal band gap and good thermal stability. However, CsPbI3 perovskite solar cells (PSCs) significantly suffer from photovoltage deficits because of serious interfacial energy losses within the PSCs, which to a large extent affects the photovoltaic performance of PSCs. Herein, a dipolar chemical bridge (DCB) is constructed between the perovskite and TiO2 layers to lower interfacial energy losses and thus improve the charge extraction of PSCs. The results reveal that the DCB could form a beneficial interfacial dipole between the perovskite and TiO2 layers, which could optimize the interfacial energetics of perovskite/TiO2 layers and thus improve the energy level alignment within the PSCs. Meanwhile, the constructed DCB could also simultaneously passivate the surface defects of perovskite and TiO2 layers, greatly lowering interfacial recombination. Consequently, the photovoltage deficit of CsPbI3 PSCs is largely reduced, leading to a record efficiency of 21.86 % being realized. Meanwhile, the operation stability of PSCs is also largely improved due to the high-quality perovskite films with released interfacial tensile strain being obtained after forming the DCB within the PSCs.

Solution-processed CsPbBr3 perovskite films via CsBr intercalated PbBr2 intermediate for high-performance photodetectors towards underwater wireless optical communication

All inorganic CsPbBr3 perovskite is regarded as a promising candidate of halide perovskites and has attracted great attention due to its superior optoelectronic properties and stability. However, the low and unbalanced solubility of precursors and uncontrollable crystallization result in poor coverage and impurity phases in CsPbBr3 polycrystalline films, hindering the application in optoelectronic devices. In this work, a facile CsBr intercalated nanostructured intermediate based two-step method is reported for simultaneously achieving good morphology and pure phase of CsPbBr3 films. With the CsBr intercalation, the intermediate films deposited in the first step exhibit porous nanostructure and CsxPb2Br4+x crystal phase. This unique porous morphology and crystal structure favor CsBr solution penetration and Cs+ ion diffusion. First-principles calculations are conducted to investigate the phase diagram of intermediates and the diffusion kinetics of Cs+ ions in the various polymorphs. The key role of CsBr intercalation is confirmed for achieving high-quality CsPbBr3 perovskite films with features of pinhole free, pure phase, large grains, and high crystallinity. Photodetectors based on optimized CsPbBr3 films exhibit excellent performance with a peak EQE of 83%, responsivity of 0.35 A/W, and specific detectivity of 1.25×1013 Jones. Fast response speed is also achieved with rise/fall time of 1.41 μs and 2.06 μs and −3 dB bandwidth up to 800 kHz. Moreover, CsPbBr3 PD shows great potential in the application of underwater wireless optical communication due to its low background noise current under ambient light illumination. Overall, this work paves the way for further research on optoelectronic devices and their applications based on CsPbBr3 films.

Unlocking the potential of antisolvent-free perovskite solar cells: Modulating crystallization and intermediates through a binary volatile additive strategy

High-quality perovskite polycrystalline thin films are generally achieved through antisolvent-assisted crystallization, a crucial process that facilitates desolvation. However, antisolvent method is limited by issues of toxicity and fabrication complexity. Here, we introduce a “binary volatile additive” strategy using methylammonium chloride (MACl) and trifluoroacetamide (TFAA) in dimethylformamide/N-methyl-2-pyrrolidone co-solvent system, enabling end-to-end management of antisolvent-free crystallization process. Combining in-situ characterizations and DFT calculations, we prove that TFAA adjusts coordination with perovskite intermediates, facilitating solvent removal and promoting the formation of nuclei, while MACl reduces the formation energy of α-phase formamidinium-based perovskite. Moreover, TFAA not only releases the residual strain caused by MACl, but also in combination with MACl, synergistically widens crystallization window and regulates ripening process, allowing for precise fabrication of homogeneous perovskite films with suppressed defects. By employing the “binary volatile additive” approach, we achieve perovskite solar cells with a power conversion efficiency up to 22.4% and elongated storage life (93% PCE retention over 1000 hours). Our study offers a simple and sustainable approach to produce high-quality perovskite films without the acquisition of antisolvent, streamlining the fabrication process.

Preparing the In-doped lead-free Cs3Cu2I5 perovskite scintillator by a co-firing technique for its application in high-resolution X-ray imaging

The perovskite scintillators have been extensively studied recently for their merits of tunable emission spectra and simple preparation processes. However, the practical applications of perovskite scintillator-based X-ray image sensor are still impeded by inadequate radioluminescence, poor environmental stability, and low imaging resolution. Herein, we demonstrate a scalable co-firing method to fabricate high-quality lead-free Cs3Cu2I5 perovskite scintillator and an Indium (In)-doping strategy is introduced to enhance its radioluminescence performance at the same time. The In-doped Cs3Cu2I5 obtains a high PLQY of 77.9% and a relative light output of 53372 ph/MeV, which are 0.34 and 1.08 times higher than those of the undoped counterpart, respectively. The X-ray detection limit of the In:Cs3Cu2I5 can reach 150.55 nGyair/s, 36.53 times lower than the requirement for X-ray medical diagnosis. The synthesized scintillator also shows superior stability under continuous high dose X-ray irradiation of 6800 μGyair/s for 120 minutes, maintaining 95% of its initial radioluminescence intensity. Furthermore, a large-area (300 cm2) flexible perovskite scintillator film is prepared, which owns a much competitive resolution of 10 lp/mm and less distortion in X-ray imaging. This work provides a practical path for the wide application of perovskite scintillator in the field of X-ray detection and imaging in near future.

Decreased Accumulation of SnO2 Particles Results from Sodium Citrate Dispersant Assisted Chemical Bath Deposition for High Quality Perovskite Solar Cells

Electron transport layer (ETL) is a crucial part for perovskite solar cells (PSCs). However, leakage current and oxygen vacancies result from little pores grown from sol‐gel method would inevitably deteriorate the performance of ETL. In contrast, thin films prepared by chemical bath deposition (CBD) could significantly restrain the little cracks. Here, SnO2 ETL are prepared by optimized CBD process, sodium citrate (SC) is explored as an auxiliary reagent to disperse ETL, thus enhances the smoothness and conductivity of the ETL, resulting in a pore‐free flat surface morphology and decreased oxygen vacancy, which is favorable for electron transport and deposition of perovskite (PVK). The PVK film fabricated on the oxygen vacancy free substrate demonstrates high quality and decreased defect density, thus effectively prevents the non‐radiative recombination of carriers. As a result, the short‐circuit current (JSC) and open circuit voltage (Voc) of the PSC devices have been obviously improved, leading to increased photoelectric conversion efficiency from 21.03% to 22.04%. Meanwhile, the long‐term and moisture stability have been promoted simultaneously.

Perovskite‐Oxide‐Based Ferroelectric Synapses Integrated on Silicon

AbstractPerovskite‐oxide‐based ferroelectric tunnel junctions (FTJs) hold great potential for applications in non‐volatile memory and neuromorphic computing due to their unique properties. However, the challenges in synthesizing high crystalline quality perovskite oxides directly on silicon wafer limit the applications of these FTJs in conventional Si‐based integrated circuits, let alone the neural networks. Herein, perovskite oxide FTJs with an ON/OFF ratio up to 1.2×106, writing/erasing speed down to 1 nanosecond, and cycling endurance (>106) are achieved by integrating ultrathin freestanding ferroelectric perovskite oxide membranes directly on silicon wafers using a wet‐transfer method. Moreover, synapses based on these FTJs exhibit long‐term plasticity. For handwritten digits recognition task, the convolutional neural network (CNN) simulation is implemented achieving a recognition accuracy up to 98.9% based on the experimental performance, close to the result of 99.2% by software‐floating‐point‐based CNN. This work sheds light on the integration of ferroelectric perovskite oxides directly on silicon for high‐performance FTJ‐based non‐volatile memory and synaptic devices.

Enhancing Light Outcoupling Efficiency via Anisotropic Low Refractive Index Electron Transporting Materials for Efficient Perovskite Light-Emitting Diodes.

Thanks to the extensive efforts toward optimizing perovskite crystallization properties, high-quality perovskite films with near-unity photoluminescence quantum yield are successfully achieved. However, the light outcoupling efficiency of perovskite light-emitting diodes (PeLEDs) is impeded by insufficient light extraction, which poses a challenge to the further advancement of PeLEDs. Here, an anisotropic multifunctional electron transporting material, 9,10-bis(4-(2-phenyl-1H-benzo[d]imidazole-1-yl)phenyl) anthracene (BPBiPA), with a low extraordinary refractive index (ne) and high electron mobility is developed for fabricating high-efficiency PeLEDs. The anisotropic molecular orientations of BPBiPA can result in a low ne of 1.59 along the z-axis direction. Optical simulations show that the low ne of BPBiPA can effectively mitigate the surface plasmon polariton loss and enhance the photon extraction efficiency in waveguide mode, thereby improving the light outcoupling efficiency of PeLEDs. In addition, the high electron mobility of BPBiPA can facilitate balanced carrier injection in PeLEDs. As a result, high-efficiency green PeLEDs with a record external quantum efficiency of 32.1% and a current efficiency of 111.7cd A-1 are obtained, which provides new inspirations for the design of electron transporting materials for high-performance PeLEDs.

Performance Enhancement of Tin-Based Perovskite Photodetectors through Bifunctional Cesium Fluoride Engineering.

Tin halide perovskites are rising as promising candidates for next-generation optoelectronic materials due to their good optoelectronic properties and relatively low toxicity. However, the high defect density and the easy oxidation of Sn2+ have limited their optoelectronic performance. Herein, we report the treatment of the FASnI3 (formamidinium tin, FA) perovskite film by a bifunctional cesium fluoride (CsF) additive, which improves the film quality and significantly enhances the photoelectric performance. The responsivity of the perovskite-based photodetector (PD) with an optimal CsF concentration of 15% is over 60 times larger than that of the PD without CsF. It indicates that both the Cs substitution and the fluoride anion additive from CsF inhibit the oxidation of Sn2+, optimize the crystal growth, and passivate the defects, demonstrating the dual roles of the CsF additive in improving the photoelectric performance. This work offers valuable insights into the additive selection for developing high-quality tin-based perovskite films and devices.

A-site assisted perovskite crystallization via ion-exchange MOFs for high efficient and stable perovskite solar cells

Here, a novel strategy is proposed targeting the volatility of A-site cations and the disordered arrangement of perovskite grains through employing Cs+ contained metal–organic frameworks In-aip(Cs) obtained by ion-exchange and crystalline transform. Interatomic forces between Cs-O atoms split the pore channels of the pristine In-aip, endowing In-aip(Cs) with multidimensional charge transport channels. In addition, the partially freed Cs+ in the interlayer compensates for the vacancy of A-site cations during the perovskite preparation process. The In-aip(Cs) modified perovskite films have a flat morphology, large grains and excellent optoelectronic properties. Benefiting from the high-quality perovskite films and faster charge extraction, the In-aip(Cs)-modified PSCs achieved a champion PCE of 23.03%, superior to the In-aip-modified (22.29%) and control device (21.13%). More importantly, the unencapsulated PSCs modified with In-aip(Cs) exhibited outstanding humidity and thermal stability. Over a period of almost 1000 h, the unencapsulated In-aip(Cs)-modified device retained 85% of its initial PCE after storing in a glove box at 85 °C, and retained 87% of the primary PCE upon storage in ambient condition at 25 °C under a humidity of 40%.

Controlling surface morphology of Ag-doped ZnO as a buffer layer by dispersion engineering in planar perovskite solar cells

In recent years, the power conversion efficiency (PCE (%)) of perovskite solar cells (PSCs) has improved to over 26%. To enhance the photovoltaic properties of PSCs, several materials for the electron transport layer (ETL) have been investigated. Zinc oxide (ZnO) is a significant ETL due to its high electron mobility and optical transparency in PSCs. As a result of various deposition methods, ZnO ETL can be processed at low temperatures. On the other hand, based on several studies, metal-doped ZnO can facilitate electron transfer, thereby improving the performance of un-doped ZnO ETL-based PSCs. Here, to improve the PCE (%) and long-term stability of un-doped ZnO ETL-PSCs, silver (Ag)-doped ZnO 1wt% as a buffer layer is examined. In this paper, with the addition of an organic solvent (ethanol) to the dispersion of Ag-doped ZnO 1 wt% nanoparticles (NPs) in deionized (DI) water, the morphology of the buffer layer (Ag-doped ZnO 1 wt%) can be controlled. This approach focuses on reducing the wettability of the ZnO/Ag-doped ZnO 1 wt% bilayer ETLs and enhancing the stability of un-doped ZnO ETL-PSCs. According to the results, the ZnO/H2O-ethanol mixtures-Ag-doped ZnO 1 wt% bilayer ETL leads to the formation of high-quality perovskite with low defects, reducing the recombination rate, and long-term stability of un-doped ZnO ETL-PSCs in ambient conditions.

Surface Crystallization Modulation toward Highly-Oriented and Phase-Pure 2D Perovskite Solar Cells.

2D perovskites have shown great potential toward stable and efficient photovoltaic devices. However, the crystal orientation and phase impurity issues of 2D perovskite films originating from the anisotropic crystal structure and specific growth mechanism have demoted their optoelectronic performances. Here, the surface crystallization modulation technique is introduced to fabricate the high-quality 2D perovskite films with both vertical crystal orientation and high phase purity by regulating the crystallization dynamics. The solvent atmosphere condition is instituted during film processing, which promotes the formation of an oriented 2D perovskite layer in stoichiometric composition at the vapor-liquid interface and templates the subsequent film growth. The solar cells based on the optimized 2D perovskite films exhibit a power conversion efficiency of 15.04%, the record for 2D perovskites (with the perovskite slab thickness n ≤ 3 and high phase purity). The solar cells based on the highly-oriented and phase-pure 2D perovskite films also demonstrate excellent thermal and humidity stabilities.

Chitin-integrated high-quality perovskite films for efficient solar cell fabrication in ambient conditions

Manufacturing halide perovskite films through methods like large-area coating in ambient air remains a challenge due to the sensitivity of perovskite compositions to humidity, which leads to the formation of pin-holes in the films. These pin-holes compromise both the performance and stability of perovskite solar cells. In this study, we effectively mitigated the formation of pin-holes in the perovskite films by incorporating chitin, a biomaterial, using a spin coating process under ambient conditions. Moreover, chitin passivates defects in the perovskite, such as dangling bonds at grain boundaries. As a result, chitin enhances both the stability and crystallinity of the films, facilitating the production of stable and efficient perovskite solar cells in an open-air environment.

Bottom-up multi-interface modification boosts the performance of carbon-based HTL-free all-inorganic CsPbI2Br perovskite solar cells

The inferior interface quality between CsPbI2Br perovskite and the electron transport layer (ETL) as well as carbon electrode limits the stability and power conversion efficiency (PCE) of hole transport layer (HTL) free carbon-based all-inorganic CsPbI2Br perovskite solar cells (C-IPSCs). Herein, perfluoropropionic acid (PFPA) is designed as a bottom-up multiple surface defect passivator that can simultaneously passivate perovskite/TiO2 interface and perovskite/carbon electrode interface. The comprehensive experiments demonstrate that PFPA can not only optimize the electron mobility, conductivity, and band structure of the TiO2 ETL through passivating oxygen vacancies (VO), but also diffuse to the upper surface of perovskite film through grain boundaries to passivate the surface lead defects, thereby facilitating the gradient alignment of the perovskite surface energy levels with the carbon electrode. At the same time, PFPA can effectively release the tensile stress at the interface of perovskite and reduce the delocalization state of the band tail caused by lattice distortion, so as to prepare high-quality perovskite films. As a result of the above interaction, the PCE of HTL-free CsPbI2Br C-IPSCs after PFPA modification is increased from 12.24% (control device) to 14.15%. In addition, the modified unencapsulated devices show superior long-term stability and thermal stability.

Passivation of defective states in single crystal MAPbBr3 and their optoelectronic properties study

We fabricated high-quality Methylpropyl lead bromide (MAPbBr3) single crystals (SC) by introducing moderate amount electron-rich amino-terminated polyoxypropylene (PEA) additives via inverse temperature crystallization (ITC) method. The intramolecular vibrations and defective states of prepared MAPbBr3 single crystals were systemically studied by the in situ variable-temperature Fourier Transform Infrared (FTIR), X-ray photoelectron spectroscopy (XPS), the synchrotron-based X-ray absorption near edge structure (XANES) et al. We find the proper amount PEA additives would prevent the formation of intermediate states and crystal boundaries, passivating the density of defective states. The X-ray detection properties of single-crystal MAPbBr3 crystals were investigated, using both high dose and low dose X-ray photons at 40 keV in synchrotron beamlines. The photocurrent of optimized PEA-treated MAPbBr3 single crystals demonstrate better performance compared with the as-prepared single crystals. Meanwhile, the decay time of MAPbBr3 single crystal is decreased from 376 ns to 17.1 ns by Time-resolved photoluminescence (TRPL) decay measurement, owing to the defect passivation by 0.5 wt% PEA additives. The PEA-treated single crystals possess much faster decay time than the commercialized Cerium-doped Yttrium Aluminum Garnet (Ce:YAG) scintillator (∼100ns). These results help elucidate the passivation of defective states and contribute paths to manufacture high-quality single crystal perovskites for next-generation optoelectronic devices.

Interfacial Rivet to Fill Structural Defects: A Spacer Engineering Gift for 3D Solar Cells.

The combination of 2D and 3D perovskites to passivate surfaces or interfaces with a high concentration of defects shows great promise for improving the efficiency of perovskite solar cells (PSCs). Constructing high-quality perovskite film systems by precisely modulating 2D perovskites with good morphologies and growth sites on 3D perovskite films remains a formidable challenge due to the complexity of spacer-engineered surface reactions. In this study, phase-pure 2D (HA)2(MA)n-1PbnI3n+1 perovskites with a controlled number of layers (n) are separated on a large scale and exploited as interface rivets to optimize 3D perovskite films, resulting in tunable film structural defects and grain boundaries. The optimized PSCs system benefits from a reduction in non-radiative recombination, resulting in improved optical performance, higher mobility, and lower trap density. The corresponding device achieves a champion power conversion efficiency (PCE) of more than 25%, especially for voltage (VOC) and fill factor (FF). The quality and uniformity of the perovskite films are further confirmed using large-area devices with an active area of 14 cm2, which exhibits a PCE of more than 21.24%. The high-quality thin-film system based on the 2D perovskites presented herein provides a new perspective for improving the efficiency and stability of PSCs.

High-Q two-dimensional perovskite topological laser.

Quasi-two-dimensional perovskites have attracted widespread interest in developing low-cost high-quality small lasers. The nano cavity based on topologically protected valley edge states can be robust against special defects. Here, we report a high-quality two-dimensional perovskite topological photonic crystal laser based on the quantum valley Hall effect. By adjusting the position of the air holes relative to the pillar, radiation leakage in topological edge states is reduced to a large extent, electric field distribution becomes more uniform and the quality factor can be as high as 3.6 × 104. Our findings could provide opportunities for the development of high-power, stable perovskite lasers with topological protection.

Room-Temperature Processed Annealing-Free Printable Carbon-Based Mesoscopic Perovskite Solar Cells with 17.34% Efficiency.

Carbon-based printable mesoscopic perovskite solar cells (MPSCs) have promising commercial development due to the use of easily scalable printing processes and low-cost carbon material electrodes. Simplifying the preparation process of MPSCs will undoubtedly contribute to their practical application. Here, we demonstrate that efficient and stable MPSCs can be prepared at room temperature without annealing by using low boiling point 2-methoxyethanol (2-ME) and strongly coordinated N-methyl-2-pyrrolidone (NMP) as a novel mixed solvent under the synergistic effect of ammonium chloride (NH4Cl). The results show that the 2-ME/NMP mixed solvent can generate an optimized coordination environment so that uniform nucleation and crystallization of perovskites in mesopores can be achieved at room temperature without annealing by forming uniform small-sized colloids in the precursor solution. Moreover, our work for the first time introduces NH4Cl as a crystallization modulator during a room-temperature annealing-free process, effectively regulating the crystallization behavior of perovskite in mesopores and obtaining high-quality perovskites. Finally, MPSCs prepared synergistically by a room-temperature annealing-free process based on a low boiling point 2-ME/NMP mixed solvent and NH4Cl modulator achieved a champion power conversion efficiency of 17.34% while demonstrating excellent long-term air stability for over half a year. This work provides a new approach to simplifying the preparation process of MPSCs and preparing efficient and stable MPSCs through a room-temperature annealing-free process.

Ultrastable and high-performance amplified spontaneous emission in centimeter-scale inorganic CsPbBr3 single-crystal thin films

In this work, high-quality and centimeter-scale CsPbBr3 perovskite single-crystal thin films were grown using the metal-organic chemical vapor deposition method. Extremely flat surfaces without distinct grain boundaries were observed throughout the thin films. A high polarized degree of approximately 0.52 was measured from the single-crystal thin films by analyzing the polarization of the photoluminescence emission spectra. Low threshold amplified spontaneous emissions with an optical gain coefficient of 1215 cm−1 under the excitation energy of 301 μJ/cm2 and the highest value of 2857 cm−1 under the excitation energy of 1.08 mJ/cm2 were investigated under the excitation of a nanosecond laser at 266 nm. The CsPbBr3 single-crystal thin films showed excellent stability where the optical gain coefficient could be maintained over 1800 cm−1 after exposure to air for ten months. The results of this study not only provide high-quality single-crystal films for laser applications but also put forward a feasible scheme to improve the stability of the materials.

Efficient and Stable Tin-Lead Mixed Perovskite Solar Cells Using Post-Treatment Additive with Synergistic Effects.

Inhibiting the oxidation of Sn2+ during the crystallization process of Sn-Pb mixed perovskite film is found to be as important as the oxidation resistance of precursor solution to achieve high efficiency, but less investigated. Considering the excellent reduction feature of hydroquinone and the hydrophobicity of tert-butyl group, an antioxidant 2,5-di-tert-butylhydroquinone (DBHQ) was introduced into Sn-Pb mixed perovskite films using an anti-solvent approach to solve this problem. Interestingly, we find that DBHQ can act as function alterable additive during its utilization. On the one hand, DBHQ can restrict the oxidation of Sn2+ during the crystallization process, facilitating the fabrication of high-quality perovskite film; on the other hand, the generated oxidation product 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) can functionalize as defect passivator to inhibit the charge recombination. As a result, this synergetic effect renders the Sn-Pb mixed PSC a power conversion efficiency (PCE) up to 23.0 %, which is significantly higher than the reference device (19.6 %). Furthermore, the unencapsulated DBQH-modified PSCs exhibited excellent long-term stability and thermal stability, with the devices maintaining 84.2 % and 78.9 % of the initial PCEs after aging at 25 °C and 60 °C for 800 h and 120 h under N2 atmosphere, respectively. Therefore, the functional alterable strategy provides a novel cornerstone for high-performance Sn-Pb mixed PSCs.