High resolution full-color perovskite quantum dot array was realized by femtosecond laser induced forward transfer technology in Jilin University

High resolution patterning of perovskite quantum dots is important for applications including high resolution displays and image sensing. However, due to the limitation of instability of perovskite quantum dots, the existing mapping techniques involving chemical reagents and mask plates are not suitable for perovskite quantum dots. Therefore, the preparation of high-resolution full-color perovskite quantum dot arrays remains a challenge.

Recently, Professor Liu Yuefeng of Jilin University, Professor Xia Hong and Professor Sun Hongbo of Tsinghua University published a research paper "High-Resolution Patterning of Perovskite QuantumDots via Femtosecond Laser Induced" in Nano Letters Forward Transfer ". In this paper, high resolution full-color perovskite quantum dot arrays and arbitrary micropatterns are successfully realized by femtosecond laser-induced forward transfer (FsLIFT) technology. The FsLIFT technology integrates transfer, deposition, pattern, and alignment in one step and does not involve the use of masks and chemical reagents, ensuring that the photophysical properties of perovskite quantum dots are not affected. Finally, a high resolution three-color perovskite quantum dot array with 2μm linewidth is successfully realized. This work provides a promising strategy for promoting the development of various practical applications based on patterned perovskite quantum dots.

The process of preparing full-color pattern and array based on perovskite quantum dots by FsLIFT technology is shown in Figure 1a. We use femtosecond laser to realize the transfer of perovskite quantum dots based on nonlinear absorption. The femtosecond laser is focused on the interface between the film of perovskite quantum dots and the support substrate. The perovskite quantum dots cause plasma generation and expansion through nonlinear absorption. Thus, the perovskite quantum dots in the laser irradiated region can be transferred to the receiving substrate. Because the ultrashort pulse is shorter than the electron-phonon coupling time, the lattice is still "cold" during the interaction between laser and perovskite quantum dots, so no thermal damage occurs and the photophysical properties of perovskite quantum dots can be well preserved. Figure 1b-d shows a fluorescent photograph of Earth patterns based on red, green, and blue perovskite quantum dots. The experimental results show that FsLIFT technology has the ability to prepare patterned perovskite quantum dots.

Figure 1. (a) Schematic diagram of preparing perovskite quantum dot array by FsLIFT. Green (b), blue (c), and red (d) Fluorescent photographs of Earth micropatterns of perovskite quantum dots.

Before preparing full-color perovskite quantum-dot arrays, we first prepared single-color perovskite quantum-dot arrays using FsLIFT technology. Patternized perovskite quantum dot arrays of 50 μm, 20 μm and 2 μm widths in green (FIG. 2a-c), blue (FIG. 2d-f) and red (FIG. 2g-i) were successfully prepared. It can be seen that the prepared arrays not only have clear edges, but also exhibit uniform and bright fluorescence characteristics, indicating that FsLIFT technology is indeed lossless. Even at the high resolution of 2 μm, the prepared perovskite quantum dot array is completely free of pinholes and cracks.

FIG. 2. Fluorescence photographs of green (a-c), blue (d-f) and red (g-i) perovskite quantum dot arrays with different resolutions prepared by FsLIFT.

In order to verify the high accuracy of FsLIFT technology and explore the film quality of transfer perovskite quantum dot films, perovskite quantum dot films on receiving substrate and corresponding carrier substrate were characterized by SEM. As shown in Figure 3a-c, there are almost no residual perovskite quantum dots in the laser irradiation region. The boundary between irradiated area and unirradiated area is complete, clear and neat. In addition, the perovskite quantum-dot film in the unirradiated region is free of pinholes and cracks, which confirms FsLIFT's high-precision machining characteristics. The perovskite quantum dots on the carrier substrate can also be used as a material source for multiple transfers to improve the material utilization rate. FIG. 3d-f shows SEM images of perovskite quantum dot arrays with widths of 50 μm, 20 μm, and 2 μm on receiving substrates. The transfer arrays have clear edges, and the transfer results are basically consistent with the fluorescence photos. These experimental results show that the proposed FsLIFT technique can effectively prepare perovskite quantum dot arrays with original fluorescence characteristics and clear edges.

Figure 3. SEM photos of perovskite quantum dot arrays on carrier substrate (a-c) and receiving substrate (d-f) prepared by FsLIFT.

In addition to achieving high resolution patterning preparation, it is also crucial to ensure that the photophysical properties of perovskite quantum dots remain unchanged. Figure 4a shows PL spectra of spin-coated perovskite quantum dot films and patterned perovskite quantum dot films after transfer. Obviously, the position and intensity of fluorescence peak of perovskite quantum dot films before and after transfer do not move and decrease, which means that the fluorescence properties of perovskite quantum dot are almost not affected. In addition, TRPL spectra of spin-coated and transferred green perovskite quantum-dot films are almost identical, as shown in Figure 4b. After the double exponential attenuation fitting, the decay time of the spin-coated perovskite quantum-dot film at 510 nm is about 6.998 ns, while that of the transferred perovskite quantum-dot film at 510 nm is about 6.521 ns. The extremely close excited state lifetime further proves that the FsLIFT process does not increase defects and reduce the probability of excited state radiation recombination. Based on PL and TRPL results, we can infer that the photophysical properties of perovskite quantum dots can be well preserved after FsLIFT.

Figure 4. PL spectra of spin-coated and laser-transferred PQD films (a), TRPL spectra excited at 405nm and tested at 510nm (b).

Due to the flexibility of femtosecond laser direct writing system, the proposed FsLIFT technique can also be used to prepare full-color perovskite quantum dots with complex patterns. Figure 5a-c shows a full-color fluorescent photograph of a perovskite quantum dot butterfly micropattern. The prepared full-color patterns demonstrate the ability of FsLIFT technology to prepare color micropatterns according to design. For display applications, the key challenge is to precisely prepare aligned RGB sub-pixels at a specified position within the pixel. Therefore, the FsLIFT process can be used to repeatedly transfer RGB perovskite quantum-dot films to achieve high resolution full-color display applications. As shown in Figure 5d-f, full-color perovskite quantum dot arrays with sizes of 50 μm, 20 μm and 2 μm have been successfully prepared, which is of great significance for display applications. FsLIFT is a simple and flexible PQD patterning process to meet a variety of practical needs.

Figure 5. (a-c) Fluorescence photograph of full-color perovskite quantum dot pattern. Fluorescence images of perovskite quantum dot arrays with resolutions of 50 μm (d), 20 μm (e) and 2 μm (f), respectively.

This work develops an efficient, maskless, flexible and programmable FsLIFT technique for the preparation of high-precision patterned perovskite quantum dots. The technique integrates the transfer, deposition, patterning, and alignment of perovskite quantum dots in one step without the need for mask and chemical treatment. The maximum resolution of the full-color perovskite quantum dot array can reach 2μm. The patternized perovskite quantum dot films have clear edges, and their photophysical properties and film quality are well preserved. High resolution patterned FsLIFT technology can greatly promote a variety of practical applications based on perovskite quantum dots, including anti-counterfeiting, information encryption and high resolution display.

The first author of the paper is Shuyu Liang, a doctoral student at the School of Electronic Science and Engineering, Jilin University. Corresponding authors are Professors Yuefeng Liu and Hong Xia at Jilin University and Hongbo Sun at Tsinghua University. In recent years, Professor Liu Yuefeng has focused on the high resolution mapping technology of fluorescent materials, and developed a series of fluorescence material mapping schemes based on femtosecond laser processing technology, including deposition, ablation, forward transfer, etc., for applications such as near-eye display, optical imaging and fluorescence anti-counterfeiting.

Source: NetEase