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Characterization of cesium lead tri-iodide for solar cells

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posted on 2022-08-15, 10:56 authored by Sizwe SibiyaSizwe Sibiya

The dataset reports on the synthesis and characterization of titanium dioxide thin films using the spray pyrolysis method and fabrication of CsPbI3 thin film using the sequential physical vapor deposition method. The thin films were characterized using XRD, SEM, and UV-vis spectroscopy to determination of the band gaps. The materials were subsequently used to fabricate perovskite solar cells. The solar cells’ efficiency of 4% showed no dependency on the thickness of the CsI layer. 

The solution of compact-titanium dioxide (c-TiO2) thin films was prepared from a mixture of 0.5M titanium tetra-isopropoxide (TTIP) (Sigma Aldrich, purity N97.0%), and 50 mL ethanol (Sigma-Aldrich Reagent) solutions. The mixture was stirred at room temperature (25 ℃) until it produced a colorless homogeneous solution. To keep some FTO areas free of c-TiO2 coverage, the edge portions of the substrates were covered with thermal tape. Then, the substrates were placed on a hotplate. The hotplate was slowly warmed to prevent thermal strain on the glass substrates as the desired temperature of 250 ℃ was reached. The thin films were formed by spraying the c-TiO2 solution mixture on the preheated substrates, using the spray pyrolysis technique, as illustrated in Figure 3.1. For this method, a spray pressure of 3 kPa was employed, air as a carrier gas, a 20 cm nozzle to substrate diameter and a 0.5 mm nozzle diameter, and with rapid sweeps, every 60s and 15s delays between them.  Substrates were then allowed to cool to room temperature (25 ℃) naturally. Subsequently, c-TiO2 thin films were annealed at 450 ℃ for an hour and characterized.

Figure 3.2 displays the SPVD schematic for CsPbI3.The thin films of CsPbI3 were grown on cleaned and treated substrates (as described in section 3.3). CsI and PbI2 precursors were used as received (from Sigma-Aldrich). Precursor powders were introduced into the chamber using separate boron nitride crucibles labeled C1 and C2, with C2 containing CsI and C1 containing PbI2. The crucibles were placed on two separate heating coils for evaporation inside the chamber. The metallic coils were electrically separated by two switches S1 and S2 connected to an external power supply circuit, as illustrated in Figure 3.2. The turbo-pump was activated to exhaust air from the evaporation chamber until a vacuum pressure of 2×10-5 mBar was reached. With the aid of a thermocouple and quartz crystal monitor, mounted on the same level as the substrates, the film temperature and thickness were constantly monitored. The monitor was set to have a Z-factor of 1.10 and a density of 6.16 g cm-3 for the PbI2 powder. CsI thickness was also monitored with a calibrated crystal quartz monitor set with a Z-factor of 1.542 and density of 4.516 g cm-3 for the CsI powder. PbI2 was evaporated when S1 is opened while S2 is closed, and vice versa for CsI. Once the required film thickness was achieved, the shutter was closed, and the current was gradually reduced to zero. Varying the PbI2 and CsI thicknesses perfected the CsPbI3 stoichiometry. The crystallization of CsPbI3 was achieved by annealing the film at 100 ℃ for 10 minutes under an air-heated oven. Finally, using CsI (99, 9%) and PbI2 (99, 9%), the experiment was repeated for varying thicknesses of CsI (from 200 nm – 500 nm) while PbI2 is kept constant at 100 nm.

Funding

National Reseacrch Foundation (NRF)

SARCH- Celan and green energy

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Physics

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