FULL PAPER www.afm-journal.de © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1903294 (1 of 7) Electrohydrodynamically Printed High-Resolution Full-Color Hybrid Perovskites Menghua Zhu, Yongqing Duan, Nian Liu, Hegeng Li, Jinghui Li, Peipei Du, Zhifang Tan, Guangda Niu, Liang Gao,* YongAn Huang,* Zhouping Yin, and Jiang Tang* Hybrid perovskites show enormous potential for display due to their tunable emission, high color purity, strong photoluminescence and electroluminescence. For display applications, full-color and high-resolution patterning is compulsory, however, current perovskite processing such as spin- coating fails to meet these requirements. Here, electrohydrodynamic (EHD) printing, with the unique advantages of high-resolution patterning and large scalability, is introduced to fabricate full-color perovskite patterns. Perovskite inks via simple precursor mixing are prepared to in situ crystallize tunable- and bright-photoluminescence perovskite arrays without adding antisolvent. Through optimizing the EHD printing process, a high-resolution dot matrix of 5 μm is achieved. The as-printed patterns and pictures show full color and high controllability in micrometer dimension, indicating that the EHD printing is a competitive technique for future halide perovskite-based high-quality display. DOI: 10.1002/adfm.201903294 Dr. M. Zhu, Dr. N. Liu, Dr. J. Li, Dr. P. Du, Dr. Z. Tan, Prof. G. Niu, Dr. L. Gao, Prof. J. Tang Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan 430074, China E-mail: highlight@hust.edu.cn; jtang@mail.hust.edu.cn Dr. Y. Duan, Dr. H. Li, Prof. Y. Huang, Prof. Z. Yin State Key Laboratory of Digital Manufacturing Equipment and Technology Huazhong University of Science and Technology Wuhan 430074, China E-mail: yahuang@hust.edu.cn The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201903294. organic materials. [17,18] This strategy is however restricted by the relative coarse resolution over 50 μm, failing to meet the requirement for high-resolution display applications. [17–19] Besides, it is incompat- ible to introduce antisolvent in the printing process, which is necessary to obtain strongly luminescent perovskite film in the spin-coating process. [20] Therefore, no full-color, strong-luminescence, and high- resolution perovskite patterns by printing have been demonstrated so far. We chose electrohydrodynamic (EHD) [21] printing for perovskite pat- terning because of its high-resolution characteristic. The EHD printing adopts electrical force to pull the jet from nozzle, rather than pushing them through a resis- tive heater or piezoelectric transducer, exhibits unique advan- tages of high resolution (50 nm) and compatibility with wide range of inks (1–10 000 cps). [22] During the EHD printing pro- cess, the solution on the nozzle tip is polarized by applying a high voltage potential, and this leads to an intense electric field around the pendent drop, deforming it into a cone-like shape (i.e., the Taylor cone) from whose vertex a fine jet is ejected. Previous work demonstrates the compatibility of EHD printing with a wide variety of inks, ranging from quantum dots, [23] OLED, [24] proteins, [25] silver nanoparticles, [26,27] and many others, [28–30] and various 2D and 3D [31–33] high-resolution struc- tures smaller than 1 μm have been printed. Herein we first demonstrated full-color inks for direct EHD printing, optimization of the printing parameters, and high- resolution colorful patterns and pictures. The PL wavelength could be tuned by varying the halide composite (Cl, Br, and I). By optimizing the parameters of EHD printing process, high- resolution dot arrays, as well as continuous lines and films were efficiently created. A high-resolution dot matrix of 5 μm was achieved by using a small-size nozzle. Typical microarrays exhibited bright red, green, blue, and mixing RGB PL, and com- plex colorful pictures such as an apple tree and a butterfly were demonstrated with precise location. We believe that the hybrid perovskites combined the EHD printing will become a new class of candidates for low-cost, full-color, and high-resolution display. 2. Results and Discussion In order to develop directly EHD printable CsPbX 3 precursors, we first explore the preparation of CsPbX 3 inks. Generally, Electrohydrodynamic Printing 1. Introduction Hybrid perovskites have demonstrated great performance recently, such as strong photoluminescence (PL) [1–4] and electroluminescence (EL). [5–10] Perovskites achieved broad tun- able emission from violet to near infrared, high color purity with a full-width-at-half-maximum (FWHM) of ≈20 nm, and comparable external quantum efficiency over 20% to quantum dots and organic material. [5] These indicate perovskites possess enormous potential as luminescent layers for display. [11–16] For the eventual application in display, full color and capa- bility of patterning are compulsory, while high resolution is strongly preferred. To meet this requirement, the current state- of-the-art patterning strategy for perovskite is inkjet printing, which has been widely used to pattern quantum dots and Adv. Funct. Mater. 2019, 1903294