Trifunctional Trichloroacetic Acid Incorporated Mixed-Halide Perovskites for Spectrally Stable Blue Light-Emitting Diodes.

Metal halide perovskites have won great recognition in light-emitting diodes (LEDs). Nevertheless, the development of blue perovskite LEDs is facing a bottleneck in improving the device performance. Although mixed chloride/bromide perovskites can achieve pure-blue emission straightforwardly, higher chloride content will induce the challenges of low photoluminescence quantum yield and poor spectra stability resulting from the chloride vacancy defects and resultant halide ion migration under an electric field. In this work, we introduce a reliable trifunctional additive trichloroacetic acid into mixed-halide perovskites, which can provide additional chloride to fill halide vacancies, passivate the uncoordinated Pb2+ ion defects, and promote the crystallization effectively. Owning to the utilization of trichloroacetic acid, the ultimate pure-blue perovskite LED obtains stable electroluminescent spectra at 477 nm under various bias and demonstrates a 5-fold external quantum efficiency improvement (up to 6.6%).

Photopatternable and Highly Conductive PEDOT:PSS Electrodes for Flexible Perovskite Light-Emitting Diodes.

Flexible perovskite light-emitting diodes (PeLEDs) constitute an emerging technology opening new opportunities in the fields of lighting and display for portable and wearable electronics. Poly(3,4-ethylenedioxythiophene):poly(stryrenesulfonate) (PEDOT:PSS) as one of the most promising flexible electrode materials has attracted extensive attention. However, the patterning and conductivity issues of PEDOT:PSS electrodes should be addressed primarily. Here, a photopolymerizable additive is proposed to endow the PEDOT:PSS electrodes with photopatternability. Moreover, this additive can also improve the conductivity of the PEDOT:PSS electrode from 0.16 to 627 S/cm because of the phase separation between PEDOT and PSS components and conformation transition of PEDOT chains. Eventually, highly conductive PEDOT:PSS electrodes with various patterns are applied in flexible PeLEDs, demonstrating a high luminance of 25972 cd/m2 and a current efficiency of 25.1 cd/A. This work provides a facile and effective method of patterning and improving the conductivity of PEDOT:PSS electrodes simultaneously, demonstrating the great potential of PEDOT:PSS electrodes in flexible perovskite optoelectronics.

Multidentate Zwitterionic Ligand-Assisted Formation of Pure Bromide-Based Perovskite Nanosheets and Their Application in Blue Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) have demonstrated rapid development during the past decade, whereas the inferior device performance of blue ones impedes the application in full-color display and lighting. Low-dimensional perovskites turn out to be the most promising blue-emitters owing to their superior stability. In this work, a multidentate zwitterionic l-arginine is proposed to achieve blue emission from pure bromide-based perovskites by in situ-forming low-dimensional nanosheets. First, l-arginine can promote the formation of perovskite nanosheets due to the strong interaction between the peripheral guanidinium cations and [PbBr6]4- octahedral layers, enabling a significant blue-shift. Second, the carboxyl group within l-arginine can passivate uncoordinated Pb2+ ions, improving the device performance. Finally, a blue PeLED is successfully constructed on the basis of the l-arginine-modulated perovskite film, demonstrating a peak luminance of 2152 cd/m2, an external quantum efficiency of 5.4%, and operation lifetime of 13.81 min. Further, the enlightenment from this work is hopefully to be applied in rationally designing spacer cations for low-dimensional perovskite optoelectronic devices.

Basic Amino Acids Modulated Neutral-pH PEDOT:PSS for Stable Blue Perovskite Light-Emitting Diodes.

State-of-the-art external quantum efficiencies (EQEs) have exceeded 20% for near-infrared, red, and green perovskite light-emitting diodes (PeLEDs) so far. Nevertheless, the cutting-edge blue counterparts demonstrate an inferior device performance, which impedes the commercialization and industrialization of PeLEDs in ultrahigh-definition displays. As the most popular hole transport layer, poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) bears the acidic and hygroscopic drawbacks, which deteriorates the device efficiency and long-term stability of blue PeLEDs. In this work, the basic amino acids with zwitterionic characteristics are proposed to modulate the pH of PEDOT:PSS, which are arginine, lysine, and histidine. It is found that they play a triple function to the blue perovskite films: modulating the acidity of PEDOT:PSS, controlling the crystalline process, and passivating the defects at the PEDOT:PSS/perovskite interface. As a result, the utilization of neutral PEDOT:PSS leads to a significant enhancement in stability and photoluminescence quantum yield. Eventually, the pure-blue PeLEDs achieve a record EQE of 5.6% with the emission peak at 467 nm. This research proves that the interfacial engineering of hole transport layers is a reliable strategy to enhance the device efficiency and operation stability of blue PeLEDs.