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Application of tetra(dimethylamino)tin calcium in titanium ore photovoltaic ALD coating

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Perovskite photovoltaics have received extensive attention from academia and industry in recent years, and even the capital market has begun to pour huge amounts of money into this field to promote research and development and mass production. Its excellent conversion efficiency, low cost and diverse application scenarios are generally considered to be the next generation of photovoltaic mainstream technology after HJT.
 
NREL Photovoltaic Efficiency Chart (Best Research-Cell Efficiency Chart | Photovoltaic Research | NREL)
ALD plays a very important role in the various production process routes of perovskite photovoltaics. The core advantage of the ALD coating process is that it can achieve uniform coating on uneven surfaces, and the thickness can be accurately controlled by adjusting the number of cycles. However, since less than one layer of atoms grows in each cycle, the overall growth efficiency is low and the comprehensive cost is higher than that of CVD, PVD and other processes. Therefore, the ALD process is suitable for growing thin films with low thickness and high quality requirements, usually not exceeding 50nm. In perovskite photovoltaic modules, the thickness of the main perovskite layer is between a few hundred nanometers and 2 microns, so it is mainly prepared by evaporation or coating rather than ALD. The parts whose thickness meets the advantages of the ALD process are mainly the electron transport layer, the hole transport layer and the encapsulation layer.
 
Simplified perovskite structure model. ALD is mainly used in ETL (electron transport layer), HTL (hole transport layer) and encapsulation layer

There are three main structures in the current mainstream single-layer perovskite production process: formal, trans, and mesoporous structures. Among them, formal and trans are more suitable for industrial production. The growth order of the simplified formal structure is: electron transport layer ≥ perovskite layer ≥ hole transport layer, and the trans order is just the opposite.

Since perovskite materials are not tolerant to high temperatures, there are strict requirements on the process temperature of the subsequent grown materials, usually between 100-120-℃. Therefore, this poses a certain challenge to the precursor and process selection of ALD. The role of the ALD process in this type of device is mainly to achieve complete coverage with a lower thickness (5-10nm), compared with PVD, RPD and coating processes that require 30-100nm to achieve complete coverage. Due to the overall reduction in thickness, the overall efficiency of the device can be improved. However, from the perspective of film conductivity and crystallinity, low-temperature ALD films are not necessarily better than other processes.
At present, the material used for the electron transport layer is mainly SnO2, and a few structures use other materials such as TiO2. In the trans structure, due to the limitation of deposition temperature, the ALD precursor of SnO2 can only use tetrakis(dimethylamino)tin (TDMASn), and its deposition temperature can be as low as 80°C and still show excellent electron transport performance and energy level matching. The chemical properties of TDMASn precursor are relatively unstable, and it is easy to gradually deteriorate during storage and use. Even most products have begun to deteriorate when they leave the factory. It is manifested as a yellow-green color. As the degree of deterioration deepens, the viscosity will gradually increase and the vapor pressure will gradually decrease within a few weeks, resulting in instability of the ALD deposition process until it is completely deteriorated even when heated to 100°C.
The application of tetrakis(dimethylamino)tin in perovskite is mainly as a precursor material, and the protective layer of perovskite solar cells is prepared by atomic layer deposition technology (ALD). ‌ This material can be used in perovskite solar cells as a conformal diffusion barrier and a narrow bandgap perovskite protective layer, thereby improving the performance and stability of the battery.
Tetrakis(dimethylamino)tin (TDMASn) is an organic tin compound with a colorless or light yellow liquid appearance. It is sensitive to water and needs to avoid contact with incompatible substances such as humid air, water, fire sources and oxidants.
In perovskite solar cells, the film of tetrakis(dimethylamino)tin prepared by ALD technology can be used as a protective layer to improve the stability and efficiency of the battery. ‌
In order to meet the market demand for perovskite electron transport layers, our company has achieved stable mass production of TDMASn and can provide 6N tetrakis(dimethylamino)tin in grams to kilograms. Our TDMASn is a colorless or light yellow liquid with a stable vapor pressure and electronic grade purity, which is widely praised by the industry.
The following is the coating process of TDMASn
 
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