# Tightly Compacted Perovskite Laminates on Flexible Substrates via Hot-Pressing
## 1 Introduction  
Halide perovskites have exhibited intriguing properties including long carrier lifetimes, strong band-edge absorption, high photoluminescence quantum yield (PLQY), tunable emission of high color purity, low cost, and easy processing, emerging as a type of promising material for optoelectronic devices such as solar cells, light-emitting diodes, photodetectors, field effect transistors, memristors, and lasers [1; 2; 3; 4; 5; 6; 7]. Moreover, with the demands for portable, stretchable, and wearable devices enormously increasing, halide perovskites, which have exhibited mechanical flexibility [8], are a promising candidate. A number of methods have been applied for spreading halide perovskites on flexible substrates, such as doctor blading [9], spin-coating [10], slot-die coating [11], spray coating [12], vapor deposition [13], and inkjet printing [14]. [PERSON] et al. synthesized ultrathin two-dimensional (2D) CsPbBr\({}_{3}\) nanosheets on flexible substrates by ink-injecting [15], and [PERSON] et al. reported a vapor-assisted solution process to manufacture methylammonium lead iodide (MAPbI\({}_{3}\)) thin film. [PERSON] et al. demonstrated 2D FAPbBr\({}_{3}\) thin films by spin-coating, leading to ultra-flexible LEDs with a large area (3 cm\({}^{2}\)) [10]. Recently, GPa-scale high pressure (1 GPa \(\approx\) 10,000 atm), achieved through a diamond anvil cell, has been reported to induce phase transition and bandgap engineering of perovskites [16; 17; 18; 19]. For instance, the high pressure can tilt the PbBr\({}_{6}\) octahedra of methylammonium lead bromide (MAPbBr\({}_{3}\)) and destroy the long-range ordering of organic cations, leading to two phase transformations below 2 GPa and a reversible amorphization arising at approximately 2 GPa [16]. Similar phenomena were alsoobserved for \(\alpha\)-formamidinium lead iodide (\(\alpha\)-FAPbI\({}_{3}\)) at 0.3 and 1.7 GPa [17]. Apart from this, the pressure-induced optical response was investigated for a two-dimensional perovskite crystal, the photoluminescence of which was red-shifted continuously at pressures within 3.5 GPa [19]. As the pressure is increased to 60 GPa, the electronic landscapes of methylammonium lead iodide (MAPbI\({}_{3}\)) can be largely altered and may make new electronic phenomena possible, such as superconductivity which is not accessible through conventional syntheses [18]. In addition to GPa-scale pressure, pressure in the range of MPa (1 MPa \(\approx\) 10 atm), which can be easily attained in a typical mechanical testing environment, could also induce morphological and optical changes of perovskites. Pressure-induced crystallization of perovskites was observed during soft-stamp nanoimprinting, which was then used to prepare highly efficient perovskite solar cells [20]. Meanwhile, the emission spectral profile of layered perovskites was reported to be sensitive to cyclic mechanical loading in the range of tens of MPa due to the alignment of layered perovskite flakes [21]. More importantly, lamination can be achieved based on the recrystallization of perovskites, which is a promising strategy for industrial fabrication of perovskite devices since it can avoid the limitations of material choices, the issue of solvent compatibility, and device instability by forming a self-encapsulating structure [22; 23; 24]. [PERSON] et al. demonstrated a lamination process at the perovskite/perovskite interface, where two half-device stacks were independently fabricated and subsequently laminated by balancing the chemical reaction MAPbI\({}_{3}\)(s) + heat \(\rightleftharpoons\) MA(g) + HI(g) + PbI\({}_{2}\)(s) [22]. [PERSON] et al. reported laminated perovskite solar cells using two separately processed half-stacks at the interface of the charge transport layer instead of the perovskite layer [23]. However, these two cases require either chemical reaction of specific perovskite components or functional materials.