Although unique, there are still shortcomings
How far are perovskite cells from commercialization?
◎Reporter Teng Jipu Han Rong
Perovskite batteries have been "uniquely gifted" since "birth" and have received widespread attention.
It can not only be made thinner and lighter, but also has the advantages of low cost, easy preparation and high low-light efficiency.
Photovoltaic cells are devices that convert solar energy into electrical energy through the photoelectric effect, and have broad development and application prospects.
Perovskite solar cells (hereinafter referred to as perovskite cells), as a new type of photovoltaic cells, have gradually emerged in recent years.
Recently, the Ministry of Science and Technology and other nine departments jointly issued the "Science and Technology Supporting Carbon Peak Carbon Neutralization Implementation Plan (2022-2030)", which also mentioned perovskite batteries, a new type of battery.
So, what is a perovskite battery?
How is it different from traditional solar cells?
What application scenarios will there be in the future?
The reporter of Science and Technology Daily interviewed a number of experts who are deeply involved in the field of perovskite batteries.
New Photovoltaic Cell With Structure Like "Sandwich"
Perovskite batteries are evolved from dye-sensitized batteries, which refer to batteries that use perovskite materials as light-absorbing layer materials.
As a new generation of solar cells, the working principle of perovskite cells is no different from that of traditional solar cells.
Its structure resembles a "sandwich", with a typical structure having 5 layers.
The two electrodes are like two slices of bread in a sandwich, which are located in the outermost layers. The hole transport layer and the electron transport layer are next to the electrodes from the outside to the inside, and the perovskite layer is in the middle.
When sunlight shines on a perovskite cell and the photon energy of the sunlight is greater than the band gap, the perovskite layer absorbs photons to generate "electron-hole pairs".
The electron transport layer transports the separated electrons to the negative electrode; the hole transport layer transports the holes separated from the electrons to the positive electrode, and further forms a directional movement of charges in the external circuit, thereby generating current and realizing the conversion of light energy to electrical energy.
Chen Qi, a professor at the School of Materials Science and Engineering, Beijing Institute of Technology, described the working principle of perovskite cells: "If the solar cell itself is a classroom, the male and female students are electrons and holes. When the light hits the solar cell, it is like The bell rang for the end of get out of class. At this time, the male students would line up to come out through the back door, and the female students would line up to come out through the front door, thus forming a directional movement of electric charges.”
Perovskite batteries have three outstanding advantages
Due to the special materials, perovskite batteries have been "innately gifted" since "birth" and have received widespread attention.
In 2016, the "Thirteenth Five-Year Plan for the Development of National Strategic Emerging Industries" mentioned that it is necessary to "strengthen the research and development of new high-efficiency and low-cost solar cell technologies such as perovskite, dye-sensitized, and organic".
Deng Yehao, a professor and doctoral supervisor at the School of Physics of Chongqing University, said that compared with the common crystalline silicon solar cells on the market, perovskite cells have three outstanding advantages.
First, the perovskite material itself has a strong light-absorbing ability.
At the main wavelength of sunlight, the absorption capacity of perovskite materials can reach more than 10 times that of crystalline silicon.
Therefore, perovskite cells can be made thinner with comparable solar energy conversion efficiency.
"This will greatly expand product forms and enrich application scenarios." Deng Yehao said.
Second, perovskite cells have the advantages of low cost and easy fabrication.
Deng Yehao said: "Perovskite materials are synthetic materials. The raw materials themselves have no rare metals and can be prepared from solutions. Therefore, the manufacturing cost of perovskite materials is low and the preparation is easy."
Finally, perovskite materials also have the advantage of high low-light efficiency.
Under cloudy and weak light conditions, perovskite materials can not only absorb short-wave light, but also maintain the energy conversion efficiency in a relatively stable state.
This feature of perovskite materials makes perovskite cells, as a thin-film photovoltaic cell, not only can be made into single-layer cells, but can also theoretically be superimposed on the surface of various cell materials to form tandem cells, thereby effectively improving solar energy. light utilization efficiency.
Deng Yehao said that from the results measured in the laboratory, the highest conversion efficiency of crystalline silicon solar cells developed for decades is 26.7%, while the current conversion efficiency of perovskite cells can reach 25.7%. The future of mining batteries is promising.
Going out of the laboratory still needs to fill two shortcomings
Although perovskite cells have considerable advantages in theory and in the laboratory, from the perspective of industrialization, perovskite cells are still in their infancy.
This is due to its own two shortcomings, namely poor stability and efficiency loss in large-area applications.
First, there is the issue of poor stability.
Chen Qi said that although in the laboratory, perovskite cells can achieve high photoelectric conversion efficiency.
However, its practical application is still restricted by many conditions.
Sun Yuchao, chairman of Beijing Yaoneng Technology Co., Ltd., said that the industry is working in many ways to solve the problems faced by perovskite batteries.
Taking the stability problem as an example, one of the most direct means to solve this problem is to modify the perovskite material itself.
That is, through structural design, element replacement, addition of doping and other means, the material itself becomes stable and the intrinsic stability of the material is improved.
Another feasible means is to isolate external unstable factors through process and engineering means, that is, to isolate environmental factors such as water and heat, thereby reducing or even avoiding the impact of external unstable factors on materials and devices.
In this regard, Wang Wenjing, director of the Solar Cell Technology Research Department of the Institute of Electrical Engineering of the Chinese Academy of Sciences, said that isolating unstable factors from peripheral means still needs to undergo a lot of outdoor verification.
It is understood that the longest working life of perovskite batteries reported so far is often only a few thousand hours, which is much lower than that of crystalline silicon batteries.
In addition to the stability issue, the efficiency loss issue in large-area applications is another shortcoming of perovskite cells.
"In terms of efficiency, in fact, perovskite cells can be fully commercialized. However, how to expand from a small area in the laboratory to a large area in practical application scenarios is a serious challenge for its commercialization." Wang Wenjing said frankly , the perovskite cells currently manufactured in the laboratory are only the size of a fingernail, which is far from the size of the solar cells required by the market.
The perovskite material itself has a short crystallization time, and the process window time in production is only a few seconds, causing difficulties in production.
In addition, in the process of preparing perovskite cells, a dead pixel or a dust may affect the efficiency of the entire cell panel, which affects the efficiency of its large-area application.
"At present, the preparation technology of perovskite cells needs to solve two problems: how to make the perovskite film more compact and smooth, and how to ensure a clean environment and avoid the interference of factors such as dust to improve the yield. Design more advanced preparation technology, It can effectively ensure the efficiency of perovskite cells in large-area applications." Wang Wenjing said.
my country's perovskite photovoltaic technology can be expected in the future
Although there are many uncertainties in perovskite batteries, many experts in the academic community are still optimistic about their future.
Chen Qi said that at present, my country has two biggest advantages in the academic research and industrial research of perovskite batteries: first, the research group is large, and there are far more domestic enterprises and institutions researching perovskite batteries than foreign countries; second, domestic research With a huge industrial base, the photovoltaic market and photovoltaic manufacturing industry are booming in China.
"The future of my country's perovskite photovoltaic technology is promising." Chen Qi said.
In terms of the future application of perovskite cells, Sun Yuchao said that the most valuable application scenario of perovskite technology is in the field of large-scale photovoltaic power generation.
After perovskite is combined with crystalline silicon to form a tandem battery, it can greatly improve the power generation efficiency of existing photovoltaic modules, thereby further reducing the cost of power generation, accelerating the replacement of traditional fossil energy, and helping my country achieve the goal of "dual carbon".
In addition, the thickness of perovskite cells is only one-thousandth of that of crystalline silicon cells, and its flexible and lightweight characteristics make it have rich application scenarios, such as wearable power generation devices, photovoltaic glass building integration, outdoor temporary power generation equipment, etc. , and can even be applied to space power generation.
After working hard in the field of perovskite batteries for many years, Sun Yuchao and his scientific research team have witnessed that perovskite batteries have never been known to the public and gradually entered the public eye.
After learning that "Technology Supports Carbon Reaching Peak and Carbon Neutralization Implementation Plan (2022-2030)", Sun Yuchao said excitedly: "It is a good time for perovskite batteries to develop high-efficiency and stable perovskite batteries. arrive!"