How It’s Made – The Rise of Perovskites Solar Cells

• Compared with other photovoltaic materials , perovskite solar cells have shown amazing speed in improving performance. Recently, researchers such as Steve Albrecht from Berlin University of Technology reported a monolithic perovskite/silicon tandem solar cell in the main issue of Science. The certified power conversion efficiency is as high as 29.15%, and it is expected to be further improved. Nowadays, the production technology of perovskite solar cells is gradually becoming mature, and the production equipment is gradually miniaturized and convenient. Following early pivotal experiments in 2009 and 2012, there has been a surge of interest in these production devices, and efforts are now being made to further optimize their performance and find a viable route to commercial application. In this article, we will take you through the manufacturing process and related technologies of perovskite solar cell materials.
  

• Preparation of Perovskite Photovoltaic Thin Film Materials

  The preparation process of solar cells is mainly divided into thin film preparation and subsequent processing. There are mainly two types of thin film preparation technologies: liquid spin coating and vacuum coating. Spin coating technology is easy to implement in the laboratory due to its simple equipment and easy and fast construction. However, its scale expansion is poor, and the repeatability and stability of the device and the compatibility with the subsequent processing flow are still insufficient. In terms of vacuum coating, physical vapor deposition (PVD), such as thermal evaporation, is currently more popular.
  

  
  

  For the thermal evaporation technique, the perovskite precursors are heated in a vacuum chamber so that they evaporate upward and cover the substrate. Through fine control of the process, the desired perovskite film is formed. Thermal evaporation produces thin films with excellent properties and good compatibility with other processes required in solar cell manufacturing (e.g. transport layers and metal contact layers are often deposited using PVD).

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• Summary of Thermal Evaporation Preparation Protocol

  Taking the common materials MAI and PbI2 for preparing perovskite solar cells as an example, the evaporation temperature of MAI is about 150°C, while the metal halide PbI2 needs 400°C~500°C. Compared with conventional metal thermal evaporation, the temperature is much lower, but the precision of thermal evaporation source temperature control is higher. Traditional metal thermal evaporation pays more attention to the high temperature that can be achieved (up to ~1800°C). If the traditional evaporation source is used to grow perovskite materials, it will easily lead to temperature overshoot, unstable properties of the prepared film, and even the precursor body will evaporate instantly. leading to growth failure. In addition to the lower temperature growth of perovskite photovoltaic materials, the deposition rate is also an important controlling variable. Since the deposition rate is not a direct function of temperature, the rate of each evaporation source needs to be calibrated and detected during deposition of perovskite materials. Usually in the thermal evaporation process, a crystal oscillator probe can be used to detect the evaporation rate of each evaporation source. For the conventional metal thermal evaporation process, the material reaches the substrate along a straight line from the evaporation source, and deposits a thin film on the substrate according to a law similar to the standard distribution function. However, for very volatile materials, such as MAI, a high vapor pressure first builds up above the source during evaporation, which causes the material to diffuse sideways, leading to unwanted deposition of material elsewhere in the chamber. Therefore, the deposition process of perovskite photovoltaic materials must be controlled more precisely, otherwise MAI will easily lead to contamination of crystal sensors of other materials.
  

• Professional low temperature thermal evaporation technology and equipment

  British Moorfield Nanotechnology company released low temperature evaporation (LTE) technology and related equipment based on years of experience in thin film equipment production. This allows researchers to quickly build perovskite photovoltaic thin film deposition systems with excellent performance. Moorfield Nanotechnology's equipment for perovskite solar cell preparation includes the benchtop nanoPVD-T15A, and the floor-standing MiniLab series with enhanced functions. The desktop nanoPVD - T15A can integrate metal/insulator sputtering, metal thermal evaporation, and organic evaporation functions, and can realize the combination of various preparation methods in the same equipment, bringing thin film preparation to a new level. The system is controlled by a 7-inch touch screen, with a high degree of automation, and various preparation methods can be switched freely, even at the same time. Users can prepare different films or composite films in the same equipment through flexible preparation methods. Such a low-temperature thermal evaporation system has the following advantages.
  

• Summarize

  Perovskite materials show good prospects in solar cells, vacuum evaporation coating is a promising preparation method and easy to realize industrial production. The deposition system for the preparation of perovskite thin films needs to be optimized to improve the quality of thin film materials. Moorfield Nanotechnology has a solid foundation of expertise and advanced equipment solutions, including a full range of LTE evaporation sources, process control options and complete deposition systems. In addition, Moorfield Nanotechnology also provides other professional equipment for the preparation of various materials, such as magnetron sputtering, electron beam evaporation, and nanoCVD system for rapid preparation of graphene.