Controlled on-chip fabrication of large-scale perovskite single crystal arrays for high-performance laser and photodetector integration

Metal halide perovskites have achieved rapid progress in photovoltaics due to superior optoelectronic properties and solution-based processing, reaching certified efficiencies up to 25.8%. Beyond photovoltaics, perovskite devices such as photodetectors, LEDs, lasers, and FETs show high performance, but many integrated optoelectronic applications require discrete, precisely positioned single-crystal arrays rather than continuous films. Conventional photolithography/etching are incompatible with perovskites’ poor stability in polar solvents. Prior approaches—vapor-phase conversion using seed arrays, template/capillary one-step methods, or inkjet printing—can form arrays on blank substrates but lack demonstrated on-chip alignment with pre-fabricated patterns and precise control of each pixel’s properties. This work addresses that gap by developing a one-step space confinement and antisolvent-assisted crystallization (SC-ASC) method enabling fully controlled, on-chip growth of high-quality perovskite single-crystal microplate arrays with precise position, size, and in-plane rotation control for integrated devices.

The paper reviews limitations of polycrystalline films for discrete integrated devices and the incompatibility of standard lithography with perovskites. It summarizes earlier array fabrication strategies: (1) two-step vapor-phase growth via precursor seed arrays and subsequent conversion; (2) one-step separation of precursor domains using microstructured templates and capillary forces; and (3) inkjet printing of precursor arrays followed by controlled crystallization. These methods typically target blank substrates and do not demonstrate precise on-chip alignment with pre-patterned electrodes nor per-pixel control (e.g., in-plane rotation), motivating the need for a new approach.

The authors introduce a one-step space confinement and antisolvent-assisted crystallization (SC-ASC) process integrated with conventional photolithography. Key elements: (1) Substrate engineering: Pre-pattern hydrophilic domains on otherwise hydrophobic substrates via surface functionalization to define array patterns (applicable to glass, metal electrodes, ITO, NiO-coated glass, PET, and oxide perovskites such as STO/KTO). During drop-casting, perovskite precursor solution is confined within the hydrophilic windows. (2) Space confinement: A hydrophobic glass coverslip is placed above the patterned substrate creating a vertical gap of ~20 µm to regulate solvent evaporation and the motion/extraction of the contact line, preventing residue and random grain formation. (3) Antisolvent-assisted crystallization: Exposure to antisolvent (e.g., CH2Cl2) improves crystalline quality and yields single-crystal microplates (MPs) centered in each hydrophilic window as the contact line retracts. Growth is conducted at constant temperature. The interplay of hydrophilic patterning, vertical confinement, and antisolvent crystallization yields well-aligned single-crystal arrays. Pixel size control is achieved by tuning hydrophilic window width, which sets the precursor domain volume; MPs with widths 2–8 µm and thicknesses 0.5–2.5 µm are obtained, with narrow distributions. Position accuracy is quantified using the offset between MP center and window center, maintaining D_offset/D_o below 10% across window widths (20–50 µm). The process scales to 10×10 cm substrates (25 patterns, 1250×1250 pixels) and supports arbitrary shapes (e.g., alphanumeric patterns). Composition tuning is achieved by mixing MAPbBr3 and MAPbCl3 precursors; due to MAPbCl3 solubility limits in DMF, a DMSO/DMF (1:1) solvent is used. Epitaxial-like in-plane rotation control is demonstrated by growing CsPbBr3 on STO (100) and MAPbBr3 on KTO, leveraging approximate 1.5× lattice parameter relationships, yielding aligned pixel edges and narrow rotation distributions. Structural characterization includes SEM, HRTEM/SAED revealing single-crystalline nature (e.g., MAPbBr3 (110) d=0.42 nm), and XRD showing strong (100)/(200) peaks. Optoelectronic characterization includes PL/fluorescence mapping, lasing measurements with a confocal setup and 395 nm fs pump, and electrical evaluation (trap density and mobility from device measurements).

- Large-area arrays: Homogeneous single-crystalline MAPbBr3 MP arrays fabricated over 10×10 cm (100 cm²) substrates containing 25 array patterns and 1250×1250 pixels, with well-defined square MPs (~5 µm width in demonstration) and sharp edges. - Process controls: Space confinement and antisolvent are critical; removing antisolvent leads to irregular shapes; removing confinement accelerates evaporation and causes random small grains. - Crystallinity: HRTEM shows (110) planes (d=0.42 nm); SAED shows single set of sharp spots consistent with cubic MAPbBr3. XRD exhibits strong (100) at 14.91° and (200) at 30.16°, matching cubic MAPbBr3; smooth, flat surfaces observed by SEM. - Pixel dimension control: MP width tunable 2–8 µm; thickness 0.5–2.5 µm, approximately linear with hydrophilic window width. Example distributions for 20 µm windows: width ~0.9–1.4 µm and thickness ~2.4–3 µm (as reported). - Position accuracy: Average offset D_offset increases modestly (1→4 µm) as window width increases 20→50 µm, but deviation ratio D_offset/D_o remains <10%, indicating precise positioning. - Substrate versatility: Arrays fabricated on glass with Cr, ITO, or NiO films, and on flexible PET, showing uniform green fluorescence under UV. - In-plane rotation control (epitaxy-assisted): CsPbBr3 on STO (100) and MAPbBr3 on KTO show well-aligned pixel edges; rotation angles confined to −2° to 2° on STO with ~60% at 0°, while glass shows random rotation across full range. - Material quality: Trap density ~1.05×10^12 cm^−3 and mobility ~111.4 cm^2 V^−1 s^−1 for MPs. - Multicolor library: MAPbBr3−xClx (x=0,1,2,3) single-crystal arrays achieved by precursor mixing (DMSO/DMF 1:1), with PL peaks at 542, 502, 464, and 410 nm and bandgaps increasing from ~2.31 to ~3.0 eV as Cl content rises. EDS confirms homogeneous elemental distribution (e.g., MAPbBr2Cl Pb:Br:Cl ≈ 1:1.9375:0.9688 near 1:2:1 stoichiometry). - Microcavity lasing: Individual MPs act as high-quality WGM microcavities with Q factor ~2915 and lasing threshold ~4.14 µJ cm^−2; lasing modes tunable via MP dimensions. - Device integration: Direct on-chip fabrication on patterned electrodes enables a vertical photodetector array with stable photoswitching and imaging of input patterns, demonstrating feasibility for integrated systems.

The SC-ASC method overcomes key barriers to on-chip perovskite single-crystal array fabrication by integrating photolithographic pattern definition with solution growth under space confinement and antisolvent control. This yields precise pixel placement (deviation ratio <10%), tunable size, and high crystal quality, addressing the need for discrete, well-aligned perovskite elements for integrated optoelectronics. Demonstrated epitaxy-assisted rotation control on STO/KTO introduces per-pixel orientation control, important for anisotropic optical modes and device uniformity. The multicolor MAPbBr3−xClx libraries extend spectral tunability while maintaining single-crystal quality. High-Q WGM lasing with low threshold validates optical cavity quality, and the directly fabricated vertical photodetector arrays with stable photoswitching and imaging capability showcase seamless integration with pre-patterned electrodes. Collectively, these results indicate that SC-ASC provides a scalable, versatile platform for integrated photonics and optoelectronics requiring precise single-crystal arrays.

This work presents a fully controlled, on-chip fabrication approach (SC-ASC) for large-area perovskite single-crystal microplate arrays with precise control over pixel position, size, and in-plane rotation. The method is compatible with diverse substrates (including patterned electrodes and flexible substrates), supports compositional tuning to build multicolor libraries, and yields high-quality crystals enabling low-threshold WGM lasing and integrated photodetector arrays capable of imaging. The approach offers a practical manufacturing route toward integrated perovskite photonics and optoelectronics. Potential future directions include extending SC-ASC to broader perovskite chemistries and heterostructures, further optimizing epitaxial relationships for orientation control, scaling device architectures (e.g., large-area imaging arrays), and investigating long-term environmental stability and encapsulation strategies for integrated systems.