Direct in situ photolithography of perovskite quantum dots based on photocatalysis of lead bromide complexes

Photolithography has shown great potential in patterning solution-processed nanomaterials for integration into advanced optoelectronic devices. However, photolithography of perovskite quantum dots (PQDs) has so far been hindered by the incompatibility of perovskite with traditional optical lithography processes where lots of solvents and high-energy ultraviolet (UV) light exposure are required. Herein, we report a direct in situ photolithography technique to pattern PQDs based on the photopolymerization catalyzed by lead bromide complexes. By combining direct photolithography with in situ fabrication of PQDs, this method allows to directly photolithograph perovskite precursors, avoiding the complicated lift-off processes and the destruction of PQDs by solvents or high-energy UV light, as PQDs are produced after lithography exposure. We further demonstrate that the thiol-ene free-radical photopolymerization is catalyzed by lead bromide complexes in the perovskite precursor solution, while no external initiators or catalysts are needed. Using direct in situ photolithography, PQD patterns with high resolution up to 2450 pixels per inch (PPI), excellent fluorescence uniformity, and good stability, are successfully demonstrated. This work opens an avenue for non-destructive direct photolithography of high-efficiency light-emitting PQDs, and potentially expands their application in various integrated optoelectronic devices.

Curing results of different monomers in inks.

Entry Monomers
Curing results under 405 nm light (3 W) 1 1 TTMP + 1 TAIC Cured/30 s 2 2 TTMP Uncured/120 s 3 2 TAIC Uncured/120 s Note: a) all entries above were conducted by adding monomers in the perovskite precursor solution with the same concentration. The perovskite precursor solution was prepared by mixing MABr and PbBr2 at a mole ratio of 2:1 in the mixture of DMF and DMSO (v/v = 4:1); b) the numbers before monomer abbreviations are the ratio of monomers; (c) UV LED of 405 nm (3 W) was used to irradiate samples from the same distance in the meantime.
Supplementary Fig. 1 Curing results of different monomers in inks. Photograph of entries 1, 2, 3 in Supplementary Table 1 after 405 nm UV irradiating for 30 s, 120 s, 120 s respectively. The scale bar is 1 cm. Note that the cured products are marked by a red arrow in the figure.
30 s 120 s 120 s 1 2 3 Supplementary Fig. 2 FT-IR spectra of the PPR and cured PPR for thiol-ene polymerization analysis. a FT-IR spectra between 2670 and 2380 cm -1 , where the peak at 2527 cm -1 represents the vibration of the thiol group. b FT-IR spectra between 3160 and 3020 cm -1 where the peak at 3080 cm -1 represents the vibration of ethenyl group. These measurements were performed by placing 50 μL of sample on the ATR crystal plate. The UV LED (365 nm, 5 W) radiated onto the sample from a distance of 1 cm centered at the ATR crystal plate. Both peaks decayed after exposing PPR for 100 s. Source data are provided as a Source Data file. Supplementary Fig. 3 Chemical structures and curing results. a Ethenyl monomers (TMPTMA: Trimethylolpropane trimethacrylate, TAIC: Triallyl isocyanurate; IATE: isocyanuric acid tris(2acryloyloxyethyl) ester). b Thiol monomers (PTMP: Pentaerythritol tetra(3-mercaptoproionate); TTMP: Trimethylolpropane tris(3-mercaptopropionate); BBT: 1,4-Butanediol bis(thioglycolate)). c Photograph of curing results of different combinations within 30 min UV light irradiation, each combination was prepared by mixing certain volume of 0.15 M perovskite precursor solution and monomers with identical amount of thiol group and ethenyl group, then irradiated by a 365 nm UV light from the same distance. Uncured/120 s Note: a) all entries above were conducted by blending monomers and additives in the perovskite precursor solution with the same concentration. The perovskite precursor solution was prepared by mixing MABr and PbBr2 at a mole ratio of 2:1 in the mixture of DMF and DMSO (v/v = 4:1); b) the numbers before monomer abbreviations are the ratio of monomers; c) UV LED of 365 nm (5 W) was used to irradiate 300 μL liquid of each entry from the same distance.   4 MABr Uncured Uncured Uncured Uncured Note: a) all entries above were conducted by blending reagent salts and monomers in the DMSO solvent, where the monomers are equal mole TAIC and TTMP with certain concentrations; b) the numbers before reagent salts are assigned to the ratios; c) 365 nm UV light (~10 mW cm -2 ) was used to irradiate 200 μL liquid of each entry; d) The conversion rate shown here was determined by measuring the volumes of liquid residues and comparing with the original volume of inks.   Uncured/60 s Uncured/140 s Uncured/60 s Note: a) all entries above were conducted by blending reagent salts and monomers in the DMSO solvent, where the monomers are equal mole TAIC and TTMP with certain concentrations; b) the numbers before reagent salts are assigned to the ratios. c) 400 μL liquid of each entry was respectively irradiated by 311nm UV LED (5 V), 365 nm UV LED (20 W) and 405 nm UV LED (3 W).   1 TTMP + 1 TAIC 2 PbBr2 4.0 Note: a) all entries above were conducted by blending reagent salts and monomers in the DMSO solvent; b) the numbers before reagent salts and monomers are assigned to the ratios. Table 7 Curing results without and with OA as an additive.

Entry
Additive Curing results under 365 nm light (~10 mW cm It is clear that the largest change of color, from light yellow to dark brown, was illustrated in the one with both perovskite precursors and aniline under UV irradiation, implying the acceleration of the reaction by applying lead bromide complexes and UV light. Furthermore, the UV spectra and the line graph ( Supplementary Fig. 12b, c) also confirmed the acceleration of the photocatalytic effect by lead bromide complexes. This phenomenon can be explained that the lead bromide complexes can deliver holes to the amido of aniline once exposed to UV light. The photocatalytic capacity of lead bromide complexes on aniline enables us to believe that the lead bromide complexes can work on other rich radical reactions.   1 Note: all data were counted by ImageJ software based on the patterned aways of blue PQD-polymer dots prepared according to the Methods. Errors were determined by standard deviantion (SD) and were illustrated in Fig. 4e as error bars. The origin PL intensity of 196 pixels were presented in Soure Data file. Supplementary Fig. 15 Laser scanning confocal 3D microscope image of the blue PQD-polymer film with stripes of 100 μm period on the VTMS modified glass, which was prepared based on the direct in-situ photolithography method with the blue PPR described in the Methods. and Lewis acid PbI2. 2,3 The PL intensity increased with increasing annealing temperature from 90°C to 130°C (Supplementary Fig. 18a Fig. 18c).
Supplementary Fig. 19 Fluorescence images of multiple color PQD patterns. a Red and green double color patterned film with squares of 500 μm. b Red, green and blue three color patterned film with squares of 250 μm. An intermediate layer of 300 nm thickness SiO2 was deposited before patterning another emitting layer, which did not affect the optical properties of the final patterns. . c Remnant PL intensity for the film without initiators versus storing time in atmosphere with average humidity of 54%. All films were prepared based on the direct in-situ photolithography method with the green PPRs described in the Methods, while the films labeled "with initiators" in the graphs were deliberately introduced 2 w% initiators. Source data are provided as a Source Data file. a b c Supplementary Fig. 23 Stability test for MAPbBr3-polymer films against deterioration of solvents. a Fully exposed films fabricated via the direct in-situ photolithography method were completely soaked at rest in the water and ethanol (EtOH) at room temperature. b Remnant PL QY recorded from (a). Source data are provided as a Source Data file.