Thermally evaporated perovskite light-emitting diodes (PeLEDs) are compatible with existing OLEDs evaporation processes. However, inadequate crystallization control during vacuum deposition leads to poor crystal morphology and increased defect states, which is particularly severe for blue perovskites due to their wider band gap, severely limiting device performance. To address this issue, we proposed a crystallization regulation strategy employing alkylbiguanide hydrochlorides. The alkyl chain length modulates the molecular electrostatic potential and steric hindrance, thereby tuning precursor interactions to realize controllable crystallization and effective defect passivation. Through systematic comparison of alkylbiguanide hydrochlorides with different alkyl chain lengths, the interaction mechanisms between these additives and perovskites were elucidated. Specifically, buformin hydrochloride (BFCl) with an optimal alkyl chain length promotes the formation of perovskite films featuring low defect density and preferred crystal orientation, which enables the fabricated PeLEDs to achieve external quantum efficiencies (EQEs) of 12.93%@407 cd·m−2 (emission peak@479 nm) and 9.47%@236 cd·m−2 (emission peak@476 nm), rendering the device performance at the first-class level in the field of thermally evaporated pure blue PeLEDs.

Perovskite light-emitting diodes (PeLEDs) fabricated through thermal evaporation are well suited for large-scale industrial production, owing to their compatibility with existing display panel manufacturing lines. However, the performance of all-evaporated PeLEDs lags behind that of their solution-processed counterparts, primarily due to the high defect density in evaporated perovskite films. Here we develop a sequential deposition combined with organic intercalation (SDOI) strategy to fabricate high-quality perovskite films by incorporating the multifunctional organic molecule phenformin hydrochloride (PFCl) into the perovskite crystallization process. The PFCl intercalation effectively prevents direct contact between the Cs and Pb precursors, thereby boosting the formation of reduced-dimensional perovskite films with highly uniform crystallographic orientation. Moreover, PFCl effectively passivates various types of defect, serving a dual role as both an organic spacer cation and a passivating agent. As a result, we demonstrate SDOI-based sky-blue PeLEDs with an external quantum efficiency of 20.12% and a maximum luminance of 23,704 cd m-2. We also apply the SDOI strategy for the fabrication of high-performance green PeLEDs, demonstrating the method's generality. Moreover, we integrate the SDOI-based all-evaporated PeLEDs into thin-film transistor-driven active-matrix display panels, demonstrating the potential of the SDOI strategy for display applications. Our SDOI strategy paves the way for efficient all-evaporated PeLEDs and their scaling up for practical applications.

ABSTRACT To accelerate the reverse intersystem crossing (RISC) process of multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters, constructing hybridized long‐range charge‐transfer (LRCT) and short‐range charge‐transfer (SRCT) states within MR‐TADF molecules is a promising strategy. However, the conventional hybrid LRCT‐SRCT strategy proves less effective in enhancing the performance of deep‐blue emitters. In this study, we propose a novel triple‐LRCT‐channel strategy to markedly enhance spin‐orbit coupling (SOC) interactions in deep‐blue LRCT/SRCT type TADF emitters. Based on the pronounced differentiation among the excited states enabled by this strategy, the proof‐of‐concept emitter DABNA‐CN‐PXZ exhibits multiple RISC channels, resulting in a tenfold faster RISC rate than its MR prototype. The corresponding device achieves a high maximum external quantum efficiency of 24.4% and a narrow FWHM of 24 nm, which ranks among the lowest reported for boron‐nitrogen‐based LRCT/SRCT type TADF emitters, arising from the judicious selection of substituents in DABNA‐CN‐PXZ that enables precise control over molecular rigidity and LRCT characteristics. These results demonstrate that DABNA‐CN‐PXZ is among the purest deep‐blue LRCT/SRCT type TADF emitters, delivering excellent device performance under BT.2020‐compliant conditions and thus validating the superiority of our molecular design strategy.

Thermally evaporated perovskite light-emitting diodes (PeLEDs) hold immense potential for future applications in the display industry. However, the performance of blue PeLEDs is far behind, one of the most important reasons is the lack of suitable hole-transporting materials. Herein, the study designs and synthesizes a new class of self-assembled monolayer (SAM) materials, namely, (2-(3,6-bis(4-formylphenyl)-9H-carbazol-9-yl)ethyl)phosphonic acid ( C-2PACz) and (2-(3,6-bis(4-(methylsulfonyl)phenyl)-9H-carbazol-9-yl)ethyl)phosphonic acid ( S-2PACz) . First, the phosphonic acid is induced to form bidentate bonds with ITO. Second, the strong electron-withdrawing groups are integrated to increase the electron cloud density of the termini contacting with perovskite, which enhances the electrostatic interaction with the Pb 2+ , reduces the interfacial defects. These advantages improve their carrier transport ability and reduce the non-radiative recombination at the interface. Meanwhile, it is found that compound C-2PACz possessing the smaller steric hindrance makes the SAMs have a more homogeneous film and a better interfacial passivation effect. By employing C-2PACz as hole-transporting layer in blue PeLEDs with metal halides as the emitting layer, the device exhibits a high brightness (1843 cd m −2 ) and a maximum external quantum efficiency (10.41% @65.59 cd m −2 ), which among the best of reported thermally evaporated sky-blue PeLEDs. The work provides new insights into design strategies for dual-function SAMs to achieve higher performance in PeLEDs.

The two/three-dimensional (2D/3D) heterojunctions hold promising prospects for improving the performance and stability of perovskite optoelectronic devices. However, the ultrathin thickness of 2D perovskite capping layer makes it difficult to directly obtain the characteristics of 2D/3D heterojunctions, leading to insufficient understanding of its compositional and configurational details. Here, we systematically investigated the heterojunction composition by precisely controlling the thickness of 3D perovskite layer using vacuum deposition techniques. Surprisingly, contrary to the traditional view that the 2D perovskite layer contains only 2D or quasi- 2D phases, we found that zero-dimensional (0D) Cs4Pb(Br/Cl)6 and 3D CsPb(Br/Cl)3 grains exist alongside quasi- 2D perovskite grain in the quasi-2D perovskite capping layer. By carrier dynamics analysis, we proposed a 0D-3D cascade model to elucidate the anomalous electrical performance enhancement. By introducing a multifunctional additive PEATFA to manipulate the phase distribution, the feasibility of the model was verified and the cascade effect was further enhanced, resulting in a maximum external quantum efficiency of 8.92 %, representing the optimal performance of blue PeLEDs fabricated by vacuum deposition. This work deepens the understanding of 2D/3D heterojunctions and provides a new research path to study 2D/3D heterojunctions.

Metal halide perovskites have become one of the most competitive new-generation optoelectronic materials due to their excellent optoelectronic properties. Vacuum evaporation can produce high-purity and large-area films, leading to the wide application of this method in the semiconductor industry and optoelectronics field. However, the electroluminescent performance of vacuum-evaporated perovskite light-emitting diodes (PeLEDs) still lags behind those counterparts fabricated by solution methods. Herein, based on vacuum evaporation, 3D perovskite films are obtained by three-source co-evaporation. Considering the unique quantum well structure of quasi-2D perovskite can significantly enhance the exciton binding energy and improve the radiative recombination rate, leading to a high photoluminescence quantum yield (PLQY). Subsequently, the highly stable and low-defect-density quasi-2D perovskite is introduced into 3D perovskite films through post-treatment with phenethylammonium chloride (PEACl). To minimize the degradation of film quality caused by PEACl treatment, a layer of guanidinium bromide (GABr) is vacuum evaporated on top of PEACl treatment to further improve the quality of emitting layer. Finally, under the synergistic post-processing modification of PEACl and GABr, blue PeLEDs with a maximum external quantum efficiency (EQE) of 6.09% and a maximum brightness of 1325 cd/m2 are successfully obtained. This work deepens the understanding of 2D/3D heterojunctions and provides a new approach to construct PeLEDs with high performance.

Self-assembled monolayers (SAMs) have exhibited widespread application in PeLEDs. However, most SAM molecules are amphiphilic, prone to forming micelles in solutions, which affects the uniformity of the film. In this work, we employed two SAM molecules to construct a hybrid SAM. By reducing the concentration of each component below the critical micelle concentration, the formation of micelles is inhibited. Additionally, the stability of mixed micelles was decreased through steric hindrance and hydrophobicity between different SAM molecules. SAM micelle formation is inhibited, resulting in more complete coverage of the buried interface. By utilization of this hybrid SAM, the thermally evaporated green PeLED achieved an EQE of 13.28%, representing advanced level performance in this field. Moreover, the devices maintained a high EQE of 8.30% at high current densities (@ 110 mA cm-2). This strategy offers a viable approach to circumvent the limitations associated with SAMs in PeLEDs, thereby enhancing their application potential.

The fabrication of perovskite light-emitting diodes (PeLEDs) with vacuum deposition shows great potential and commercial value in realizing large-area display panel manufacturing. However, the electroluminescence (EL) performance of vacuum-deposited PeLEDs still lags behind the counterparts fabricated by solution process, especially in the field of blue PeLEDs. Here, the fabrication of high-quality CsPbBr3- x Clx film through tri-source co-evaporation is reported to achieve high photoluminescence quantum yield (PLQY). Compared with the conventional traditional dual-source co-evaporation, the tri-source co-evaporation method allows for freely adjustable elemental ratios, enabling the introduction of the lattice-matched Cs4 Pb(Br/Cl)6 phase with the quantum-limited effect into the inorganic CsPb(Br/Cl)3 emitter. By adjusting the phase distribution, the surface defects of the emitter can be effectively reduced, leading to better blue emission and film quality. Further, the effects of Cs/Pb ratio and Br/Cl ratio on the PLQY and carrier recombination dynamics of perovskite films are investigated. By optimizing the deposition rate of each precursor source, spectrally stable blue PeLEDs are achieved with tunable emission ranging from 468 to 488 nm. Particularly, the PeLEDs with an EL peak at 488 nm show an external quantum efficiency (EQE) of 4.56%, which is the highest EQE value for mixed-halide PeLEDs fabricated by vacuum deposition.

Thermally evaporated perovskite light-emitting diodes (PeLEDs) are promising for next-generation displays, yet process-compatible passivation strategies for performance enhancement are still lacking. Herein, an effective in- situ surface passivation strategy using post-evaporated metformin hydrochloride (MFCl) is introduced in co- evaporated PeLEDs. MFCl post-deposited onto the perovskite film induces surface reconstruction, improving surface uniformity and healing grain boundaries. Additionally, MFCl penetrates deeply into the perovskite film, passivating both undercoordinated Pb and halide ions at grain boundaries. By employing this strategy, we achieve thermally evaporated blue PeLEDs with a peak external quantum efficiency (EQE) of 9.2 % and a maximum luminance of 1820 cd/m-- 2 (- |-), emitting at a peak wavelength of 488 nm. Furthermore, this strategy effectively suppresses ion migration, significantly enhancing the spectral stability and device lifetime of the blue PeLEDs. This work provides a process-compatible defect passivation strategy for thermally evaporated PeLEDs, laying the foundation for further advancements in this field.

Perovskite light-emitting diodes (PeLEDs) based on thermal evaporation technique have demonstrated great potential in newly-developed wide color gamut display applications. However, it is still a challenging task to obtain high efficiency thermally evaporated blue PeLEDs. One of the key issues is the lack of desirable functional materials with both hole transport function and perovskite buried interface modification function, which can alleviate the accumulation of high density of deep-level defects between hole transport layer (HTL) and perovskite emitting layer (EML) and weaken the interfacial nonradiative recombination process. In this study, we developed a new multifunctional wide-bandgap self-assembled monolayers (SAMs) suitable for thermally evaporated blue PeLEDs, named (2-(3-bromo-6-(4-formylphenyl)-9H-carbazol-9-yl)ethyl)phosphonic acid (CZPC). The interactions between the carbonyl groups (C = O) contained in CZPC and uncoordinated Pb2+ are critical for improving crystallinity and suppressing nonradiative losses at the buried perovskite-hole transporter interface. In addition, the phosphonic acid groups bonding with indium tin oxide (ITO) can form a self-assembled monolayer to facilitate carrier injection and transport. Finally, simplified thermally evaporated sky-blue (488 nm) PeLEDs utilize CZPC as HTL and no additional functional layers such as hole injection layer are used show excellent device performance with a maximum external quantum efficiency (EQE) of 5.42 %, accompanied by the CIE color coordinates of (0.07, 0.25) and a full width at half maximum (FWHM) of 24 nm. This work lays a foundation for the further exploration of SAMs on high-performance thermally evaporated blue PeLEDs towards ultra-high resolution display applications.

The co-evaporation technique shows great potential for producing perovskite films. However, there is a lack of research on the growth process and the film characteristics of co-evaporated perovskite. Herein, we found that pre-frozen substrates and post-annealing can synergically improve the performance of co-evaporated blue perovskite light-emitting diodes (PeLEDs). The optimized blue PeLEDs obtained an impressive peak external quantum efficiency (EQE) of 7.2%, which is the best reported for co-evaporated blue PeLEDs till now. The systematic investigation found that the pre-frozen substrates can facilitate the exotherm of vaporized precursor molecules near the interface, leading to more efficient nucleation and constraining grain enlargement. Furthermore, low-temperature annealing (LTA) can efficiently suppress compositional segregation and release residual compressive strain in co-evaporated perovskite films while retaining the advantages of pre-frozen substrates. This work provided deeper insights into perovskite films prepared by co-evaporation and offered a feasible strategy for enhancing the performance of the co-evaporated PeLEDs.

Quasi-2D perovskites have emerged as a promising material for the fabrication of perovskite light-emitting diodes (PeLEDs) owing to their excellent photoelectronic properties. The realization of efficient PeLEDs relies critically on the effective energy transfer and radiation recombination in quasi-2D perovskites. However, the performance of PeLEDs is hindered by the disordered distribution of n-values and a large number of surface defects in quasi-2D perovskites, which significantly impacts their practical application and further development. Herein, a passivation strategy utilizing the bifunctional additive sodium hexafluorophosphate (NaPF6) is proposed. The introduction of PF6- anions substantially inhibits the formation of low-n phases, which can accelerate the effective energy transfer within the quasi-2D perovskites. Furthermore, the lone electron pairs in PF6- anions can pair with the uncoordinated Pb2+ cations of perovskites to passivate defects. As a result, the champion green PeLED modified with NaPF6 exhibits a remarkable external quantum efficiency (EQE) of 20.13% and a current efficiency (CE) of 67.54 cd A-1, which represents a significant improvement compared with the 11.26% EQE and the CE of 37.38 cd A-1 of the control sample. A passivation strategy using the bifunctional additive sodium hexafluorophosphate (NaPF6) is proposed. By adjusting the phase distribution and passivating the defect in the quasi-2D perovskite film, the champion green perovskite light-emitting diodes (PeLED) modified with NaPF6 exhibits a remarkable external quantum efficiency (EQE) of 20.13%, which represents a significant improvement compared with the 11.26% EQE of the control sample. image

Multisource coevaporation is such a promising method for the preparation of perovskite films. However, there is limited research about the effects of the buried interface on thermal-evaporated perovskite light-emitting diodes (PeLEDs). In this study, the effects of buried interfaces on thermal -evaporated all-inorganic perovskite films are systematically investigated. It is found that the low-surface-energy buried interface promotes the formation of columnar grain by suppressing heterogeneous nucleation, and functional groups on the high-surface-energy interface have a significant effect on the actual element ratio of the film. The substrate temperature can affect the nucleation and film-formation kinetics of the columnar grains. As a result of the synergistic strategy, a peak external quantum efficiency (EQE) of 8.6% is achieved in the green PeLEDs with a stable emission peak at 516 nm, which is among the best thermal-evaporated PeLEDs reported. This work provides an insight into the preparation of perovskites by thermal evaporation and builds the groundwork for future studies.