DEVELOPMENT AND CHARACTERIZATION OF MAPbI3 PEROVSKITE THIN FILM FOR SOLAR CELLS

ABSTRACT

Recently, perovskite-structured materials have been attracting great deal of attention because of their unique properties. It is crucial to emphasize that the perovskite materials employed in solar cells exhibit resistance to environmental factors, temperature fluctuations, and humidity. This work outlines the method for forming perovskite thin films for solar cells. The study investigated the use of zinc oxide in place of titanium oxide on FTO glass during the formation of perovskite thin films. Graphite was employed as contacts instead of metals, and spectral analysis was conducted using XRD spectroscopy.

АННОТАЦИЯ

В последнее время материалы со структурой перовскита привлекают большое внимание из-за своих уникальных свойств. Важно подчеркнуть, что материалы перовскита, используемые в солнечных элементах, проявляют устойчивость к факторам окружающей среды, колебаниям температуры и влажности. В этой работе описывается метод формирования тонких пленок перовскита для солнечных элементов. В исследовании изучалось использование оксида цинка вместо оксида титана на стекле FTO во время формирования тонких пленок перовскита. Графит использовался в качестве контактов вместо металлов, а спектральный анализ проводился с помощью рентгеновской дифракционной спектроскопии.

Keywords: MAPbI₃, perovskite thin film, spin coating, XRD, fluorescence.

Ключевые слова: MAPbI₃, тонкая пленка перовскита, центрифугирование, рентгеновская дифракция, флуоресценция.

Introduction.

In recent years, organic-inorganic perovskite materials have garnered significant attention from researchers due to their unique optoelectronic properties, electrical characteristics, long lifetimes, and various other features [1-2]. Furthermore, researchers have been synthesizing non-toxic, highly stable, and efficient organic-inorganic perovskite materials [3].

The development of stable iodide perovskites remains challenging even after a decade. Furthermore, producing perovskite thin films necessitates precise engineering skills to achieve high-quality material. It has been reported that a lower temperature is required for drying MAI than for drying PbI [4]. In addition, methods for forming MAPbI₃ layers by drop-coating have been described. Low-boiling solvents were utilized to prepare the MAPbI₃ solution and high-quality perovskite thin layers were formed at room temperature [5].

In the one-step perovskite layer formation, the corresponding salts were dissolved in an equimolar ratio in a solvent to form a MAPbI₃ solution. It was deposited on a cleaned glass using the spin coating method at a speed of 2500 rpm. By increasing the temperature, it was observed that the yellow layer turned into a dark brown state. That is, perovskite crystals containing MAPbI₃ were grown. To grow perovskite crystals in a layer state in a two-step method, PbI₂ and MAI₂ solutions were prepared separately and first heated to form a PbI₂ layer. Then the MAI solution was sited on the PbI₂ layer and thin film crystals were grown by heating [6].

Here we report a two-step method to produce a thin film of MAPbI₃ containing perovskite. The structural properties explored using the powder X-ray diffraction. 

Experimental.

Methyammonium iodide (99%), lead iodide (PbI₂, 99%) were purchased from Haihang Industry Co., Ltd (PRC). All solvents were analytical grade and used without any further purification.

Preparation of MAPbI₃ solution

159 mg (1 mmol) of methylammonium iodide salt and 461 mg (1 mmol) of lead(II) iodide salt were weighed on an analytical balance. These salts were dissolved in 2 ml of dimethylformamide (DMF) to form a 0.5 M solution. The solution was stirred on a magnetic stirrer for 3 hours until a clear solution was formed.

Formation of a thin layer of MAPbI₃

First, the fluorine-doped tin oxide (FTO) glass was cleaned in an ultrasonic bath using acetone, isopropyl alcohol, and distilled water 15 minutes each. ZnO was used as an electron transport layer on the FTO glass surface. For this, a required amount of ZnO paste was prepared in 96% ethanol. Using the resulting ZnO paste, a uniform layer was formed on the FTO glass (Fig. 1).

Then, the glass/FTO/ZnO layers were heated by increasing the temperature by 50˚C every 30 minutes. When the temperature reached 300˚C, the heating was stopped and the layer was cooled to a room temperature for 10 minutes. To form a MAPbI₃ containing perovskite layer on the formed glass/FTO/ZnO layer, the MAPbI₃ solution was deposited in a single-step method using the spin coating method at a speed of 1000 rpm. After the perovskite was formed, it was heated at 100 ˚C until the yellow layer turned dark brown (Figure 2).

Results and discussion.

In the preparation of sensitizers based on inorganic and inorganic-organic halide perovskite quantum dots (QDs), ZnO was used as oxide materials. Powder X-ray diffraction (XRD) samples were obtained to study the structure of the oxide material (Fig. 3).

Figure 3. XRD pattern of ZnO film

The diffraction pattern figure above corresponds to JCPDS No. 36-1451. The crystal lattice parameters are as follows: a = 3.249 Å and c = 5.206 Å, with a hexagonal structure (space group P63mc, wurtzite structure).

After MAPbI₃ was deposited on the ZnO surface, powder X-ray diffraction was used to determine its crystal structure (Fig..4). It is known that the formation of a simple cubic perovskite layer is important for solar cells. Also, volatile solvents were used to deposit the perovskite QD layer. The properties of the final material obtained using dimethylsulfoxide (DMSO), DMF, and acetonitrile (CAN_ as solvents were studied. All results showed that the layers obtained using DMF as the solvent were compatible.

Figure 4. XRD pattern of FTO/ZnO/MAPbI₃ layer

From the above diffraction pattern, it can be seen that the perovskite layer obtained by the spin coating method has a simple cubic crystal structure and a high degree of crystallinity. The diffraction pattern also shows peaks at diffraction angles of 34.4º and 69º. This can be concluded that in some parts the ZnO particles remain open, causing a signal.

After the perovskite layer is deposited, the next step is the hole transport layer (HTL). Spiro-OMeTAD (for n-i-p structure) or PTAA, PEDOT:PSS (for p-i-n structure) are often used for this layer. However, in this work, graphite (candle dust) was used for the HTL because of simplicity.

Carbon (candle soot) is a cheap and stable substitute for traditional HTLs such as Spiro-OMeTAD or PTAA. Although its efficiency is lower than that of optimized organic/inorganic HTLs, it is high in stability and easy to process. The following diagram shows the structural diagram of a carbon-based HTL perovskite solar cell (Fig. 5).

Figure 5. A) Structural diagram of a perovskite solar cell based on MAPbI₃ with carbon HTL; B) Energy level diagram of a FTO/ZnO/MAPbI₃/C perovskite solar cell.

Conclusion.

Perovskite thin film MAPbI₃ was prepared using the spin coating method. ZnO was found to be a suitable material for the ETL. XRD studies of the ETL layer were consistent with the wurtzite structure. DMF was used as a solvent to deposit the perovskite layer. A highly crystalline MAPbI3 with a simple cubic structure was formed after deposition. To obtain the perovskite solar cell, candle soot was applied directly to the surface of the MAPbI₃ layer.

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