# Effect of Methylammonium Iodide (MACI) on MAPbI\({}_{3}\)-Based Perovskite UV-C Photodetectors
## 2 Materials and Methods
### Device Fabrication Process of MAPbI3-Based Perovskite Photodetector  
Before device fabrications, the ITO coated quartz glass substrates were purified to remove any impurities such as organic or inorganic particles. The ITO-coated substrates were then subsequently cleansed using an ultrasonic bath with a mild liquid soap, IPA, acetone, and purified water (D.I. Water < 18 M\(\Omega\)) for about 15 min each. Then, any residue on the surface of the substrates was blown away by pure nitrogen gas. Subsequently, they were transferred to UV ozone treatment equipment and the contamination was removed from the surface of the substrate.  
After the cleaning process, we dropped 1.2 mL of the SnO2 colloidal solution diluted in 5.2 mL of deionized water and mixed it with a magnetic stirrer. SDBS (1 mg) was added to the diluted solution to prepare the SnO2-SDBS mixed solution.  
Next, to form the electron transport layer, the SnO2-SDBS mixed solution (500 \(\mu\)L) was dropped on the substrate and coated at 3000 rpm in a spin coater for 30 s. The samples were moved to hot plate and heated at 150 \({}^{\circ}\)C for 30 min. After that, the samples were cleaned in Ultraviolet (UV)-Ozone Cleaning Systems for 20 min to remove any impurities including moisture in the inside of coated films on the substrate before perovskite layer deposition.  
To prepare MAPbI3 perovskite precursor solution, DMF and DMSO were mixed in 10:1 \(v\)/\(v\) and PbI2 (1.4 mol), MAI (1.4 mol), and MACI (0.10 M) were solved in the DMF and DMSO mixture with magnetic stirring. The mixture process was conducted under the condition that it was stored completely unexposed from any light for 3 h (200 rpm) to form uniform particles in the perovskite layer of photo-detector devices.  
FABr chemicals were solved in various contents (0, 5, 10, 15, 20, and 25 mg) with IPA solution. The FABr solutions were transferred to a Teflon container and stirred for 1 h (200 rpm) for FABr post-processing. Subsequently, toluene (250 \(\mu\)L) was added dropwise for 15 s on the surface of the substrate during the spin coating process to form an antisolvent.  
The perovskite (MAPbI3) layer was formed on the SnO2-SDBS/ITO-coated quartz substrate with a spin-coating process at 4000 rpm for 25 s. After spin coating, the samples were treated at a temperature of 140 \({}^{\circ}\)C for 15 min on a hotplate and naturally cooled down. A spiro-OMeTAD solution was prepared as the following process; chlorobenzene solution (1 mL) contained 72.3 mg of Spiro-OMeTAD, 28.8 \(\mu\)L of 4-tert-Butyl pyridine, and 17.5 \(\mu\)L of Lithium bistrifluoromethanesulfonimide solution (ACN in 1 mL of Lithium bistrifluoromethanesulfonimidate 520 mg). The Spiro-OMeTAD solution was doped on the perovskite layer grown on the substrate and was coated at 2000 rpm for 35 s. Finally, we employed a thermal evaporator for Au deposition. An Au top electrode was thermally evaporated in a vacuum of 2 \(\times\) 10\({}^{6}\) Torr. The vertical structure of the photo detector device and the more detailed photo detector device fabrication process are shown in Figure 1a,b.