## 2 Experimental Section  
The PbS QDs were synthesized in our laboratory. Detailed information can be found in the supporting information. The QDs were dispersed on a regular glass substrate by a supercritical CO\({}_{2}\) (sc-CO\({}_{2}\)) fluid process [14]. A typical supercritical fluid deposition system consists of a CO\({}_{2}\) source (liquid CO\({}_{2}\) tank), a syringe pump (Teledyne ISCO model 260D, Lincoln, NE, USA) with a pump controller (Teledyne ISCO Series D, Lincoln, NE, USA), high-pressure stainless-steel cells, and a collection vessel. The home-made apparatus shown in Figure 1 was used for the PbS QD deposition. A thoroughly pre-mixed solution of 70 \(\upmu\)L of PbS QDs (particle size 4.7 \(\pm\) 0.5 nm, concentration 40 mg/mL) with the addition of 200 \(\upmu\)L toluene solvent was loaded into the apparatus (Figure 1a). After that, a mini glass cup was put upside down on top of the apparatus (Figure 1b), and the sample was inserted into the high-pressure stainless-steel chamber (Figure 1c). The QD film deposition procedure was performed as follows: Liquid CO\({}_{2}\) at 60 atm was introduced into the high-pressure chamber gradually until 70 atm. Afterwards, the system temperature was raised from room temperature to 40 \({}^{\circ}\)C in order to bring the liquid CO\({}_{2}\) in the reaction chamber into the supercritical state. During the heating period, the pressure inside the chamber rose to roughly 140 atm. In order to provide consistency for each deposition procedure, the pressure was increased to 160 atm. The high-pressure apparatus was then left at 40 \({}^{\circ}\)C and 160 atm for 30 min in order to ensure equilibrium. The particles were deposited by a gas-antisolvent (GAS) mechanism described previously in the literature [15], where an increasing amount of CO\({}_{2}\) altered the polarity of the toluene solvent and it became unfavorable for particle stabilization in the colloid, causing particle precipitation from the solution. Finally, the sc-CO\({}_{2}\) was vented slowly and depressurized with a flow rate of around 0.2 mL/min (CO\({}_{2}\) becomes gas at the ambient pressure), leaving a deposited PbS QD film behind. Afterwards, the sample was unloaded from the system (Figure 1d). The sample's density was approximately 2.21 mg/cm\({}^{2}\) and the average scan height (thickness) of the film was 42.85 kA (4.285 \(\upmu\)m). On the other hand, films produced by solvent deposition or the drop-casting approach show more irregular and coffee ring-shaped coverage. Comparing solvent and sc-CO\({}_{2}\) depositions, the former depends on surface tension effects at the interface of solvent and vapor, while during the sc-CO\({}_{2}\) deposition, the supercritical state eliminated the surface tension at the liquid/vapor interface due to surface-wetting instabilities that had detrimental influences on the assembly of low-defect PbS QDs films [14; 15]. Consequently, sc-CO\({}_{2}\) deposition offers a method for the production of uniform PbS QD films with consistent optical properties. Further information about the sample quality is shown in the Supplementary Material in Figures S1-S3, which show the visible difference of appearance of drop-casted films versus films deposited via the sc-CO\({}_{2}\) process, and the x-ray spectrum and the high resolution transmission microscope (HRTEM) image of the film investigated, respectively. Figure 1: Apparatus used to form the samples. (**a**) Substrate holder with a diameter of approximately 1 cm. (**b**) Sample holder with a mini beaker on top. (**c**) sc-CO\({}_{2}\) high-pressure reaction chamber, and (**d**) the final product. For the PL and absorption measurements, the sample was mounted in an optical closed-cycle helium cryostat with an operating range of 5-300 K. We exposed the sample to the up-converted 532 nm continuous wave (cw) emission of a Nd:YVO4 laser, whereas by adjusting via a lens a laser spot of \(\sim\)1 mm diameter on the film's surface, the impinging intensity was about 85 W/cm\({}^{2}\).