25.7%? High-efficiency development of perovskite

• The photoelectric conversion efficiency of perovskite solar cells reaches 25.7%. This data can be said to be very awesome. I believe that anyone who has done it knows how difficult it is for a device to achieve this parameter. It is not a day's work. The reason why the efficiency is so great, in addition to its deep foundation in the field of photovoltaic devices, is also related to the mode of teamwork in the field.
  

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• There are also many excellent achievements in high efficiency in China . In the future, if perovskite continues to develop and improve, we may learn some experience by reviewing the development history. Therefore, today we will analyze the development of high-efficiency perovskite devices.

  
  

  In the ancient period of perovskite (the first three years), two major events mainly occurred: one was its birth, and the other was the introduction of spiro materials. In 2009, Miyasaka first reported perovskite photovoltaic devices based on the structure of dye-sensitive cells, with an efficiency of 3.8%. The structural innovation of dye-sensitive cells is very large, and its principle is completely different from that of traditional photovoltaic semiconductor devices. Gratzel's series of pioneering work in the field of dye sensitivity has made great contributions to the birth and development of perovskites, including the all-solid-state perovskite based on organic hole semiconductor spiro materials that really attracted the perovskite field. The birth of the mine solar cell. Yes, spiro was actually developed by the Gratzel group as early as 1998 and used for solid-state dye sensitivity (I think if perovskite can win the Nobel Prize, Gratzel and Mitasaka must have names), these two articles are currently combined. It has been cited more than 20,000 times.

  
  

      Spiro is a very powerful material, and at least half of the success of perovskite, especially in high efficiency, is due to spiro. The energy level matching of Spiro and perovskite is very good, and its extraction of holes is also very strong. Although the stability of spiro materials has been criticized, this is another story. At least the current record-breaking device, spiro The formula has not changed much, and the status has not changed. This official account will also carry out corresponding special discussions on the subject.

  
  

  From here, perovskite has begun to pursue the dream, and the conversion efficiency has been rising year after year.

  
  

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• The increase in short-circuit current is gradual (since 2016), and there is no apparent plateau. This is mainly because the relative loss of photocurrent derived in perovskite is small, and the improvement of photocurrent is mainly by increasing light absorption (reducing the perovskite band gap and increasing the thickness of the perovskite film), reducing light loss (decreasing the coating thickness) anti-film, etc.) to achieve. Subsequent research may be one of the growth points to surpass the current best device performance if it achieves a step-by-step improvement in photocurrent.

  
  

  The fill factor FF mainly maintained two plateaus after 2016. The level of the first plateau is about 78-81, mainly due to the competition between the two electron transport layers of titanium oxide (TiO2) and tin oxide (SnO2). Both materials can help perovskite cells achieve a FF of around 80. Koreans made more TiO2 materials at that time, but relatively speaking, the preparation of SnO2 was less difficult and only required a lower sintering temperature. Especially, the commercial SnO2 precursor material successfully introduced by Mr. You Jingbi’s team can also play a good role. Effect. But what I didn't expect was that the Koreans overtook a corner on the SnO2 track in one fell swoop.

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• They slowly deposited a tin oxide transport layer in an aqueous solution via a chemical bath, pushing the device FF to a new platform. This work is still very solid, and perhaps some people have long realized that the quality and density of the film formed by the spin coating method are not the best, especially for thin electron transport layers. Although the method of CBD tin oxide can theoretically achieve better film formation quality and density, the best effect in the early stage is similar to that of spin coating, and the controllability is poor. When the Koreans do this, it can be said that they have developed a process method to the extreme. Compared with the 25.2% increase of tin oxide based on CBD for the first time this time, the main reason is the short-circuit current. The Voc and FF do not change much, and the film thickness of perovskite should be increased on the original basis. Or changing the composition of the perovskite has narrowed the band gap, but has not yet produced a larger technical generation difference.

  
  

  
  

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