Recently, the breakthrough technology of all-perovskite stacked batteries from the Wuhan University team was published in Nature magazine, pointing to the biggest pain point of industrialization, "narrow bandgap bottom batteries." Based on this technology, the team achieved one of the world's highest efficiencies in the current two-terminal all-perovskite stacked battery with a steady-state efficiency of 27.62% (third-party authoritative certification efficiency of 27.34%).
Tan Hairen, a professor at Nanjing University who has long studied all-perovskite tandem batteries, once said that the poor performance of narrow-bandgap perovskites is a key bottleneck limiting the performance of all-perovskite tandem batteries. The theoretical efficiency of all-perovskite stacked cells is as high as about 43%, which can significantly reduce the cost of photovoltaic electricity and the difficulty of manufacturing. If the relevant technology can make breakthroughs, it will have very promising development prospects.
Effectively improve industrialization pain points
In the early morning of November 9th, Beijing time, "Nature" published online the latest research results on all-perovskite tandem solar cells by the teams of Fang Guoguo and Ke Weijun from the School of Physical Science and Technology of Wuhan University. The title of the paper is "Aspartateall-in-onedoping strategy enables efficient all-perovskitetandems".
The team creatively proposed an integrated doping strategy for aspartic acid hydrochloride.Effectively improve the efficiency and stability of narrow bandgap perovskite sub-cells, and find new ways to further improve battery performance.
Professor Tan Hairen once introduced that the all-perovskite tandem battery consists of three parts: a narrow bandgap bottom battery, an interconnection layer/tunnel junction, and a wide bandgap top battery.Among them, the poor performance of narrow-bandgap perovskites is a key bottleneck limiting the performance of tandem batteries. The solution is to implement defect control.
Ke Weijun, one of the corresponding authors of this paper and a professor at the School of Physical Science and Technology of Wuhan University, also said that the insufficient narrow bandgap perovskite bottom battery is one of the stumbling blocks for the future commercial application of all-perovskite stacked batteries.
In this study, the researchers cleverly introduced aspartic acid hydrochloride (AspCl) into the bottom hole transport layer, perovskite body light-absorbing layer, and upper interface layer, developing an integrated doping strategy using the same molecular treatment. Research has found that AspCl-SnI2 and AspCl-PbI2 have very low formation energy, which is conducive to the formation of intermediates or complexes, which greatly improves the quality of perovskite films. In addition to coordinating with the perovskite precursor, AspCl molecules also have strong intermolecular hydrogen bonds. The AspCl enriched at the upper and lower interfaces of the perovskite also acts as a molecular lock between the perovskite layer and the transport layer interface, further improving the performance and stability of the perovskite material.
In addition, how to suppress the spontaneous oxidation of unstable divalent tin metal ions in narrow-bandgap perovskites is one of the major pain points in the industry. Research results show that AspCl can effectively inhibit the oxidation of divalent tin and reduce harmful tetravalent tin impurities. Further research also shows that the introduction of AspCl can passivate defects in perovskite materials, adjust the Fermi level, inhibit harmful ion migration, etc., thus enhancing the performance and stability of the device.
This simple integrated doping strategy achieves multiple functions in one fell swoop, providing a promising method for improving the performance of narrow-bandgap perovskite and all-perovskite tandem solar cells, and is also expected to promote the development of other optoelectronic fields.
Schematic diagram of battery preparation process, stacked battery structure and efficiency diagram. Source: Xinhua News Agency
Based on this, the team of Fang Guoguo and Ke Weijun simultaneously improved the efficiency and stability of the narrow bandgap perovskite sub-cell through an aspartate integrated doping strategy, achieving one of the world's highest efficiencies in the current two-terminal all-perovskite stacked cell with a steady-state efficiency of 27.62% (third-party authoritative certification efficiency of 27.34%).
According to public information, the new metal halide perovskite is a crystal material with the general molecular formula ABX3. It has the advantages of simple preparation process, high defect tolerance, high absorption coefficient, and long carrier diffusion length. It has attracted much attention in the field of optoelectronic devices and is considered to be one of the most promising photovoltaic materials of the next generation.
Among them, the photoelectric conversion efficiency of single-cell perovskite solar cells is already equivalent to that of traditional silicon-based cells, but it will be increasingly difficult to further improve its efficiency.
All-perovskite tandem cells can break through the Shockley-Quisser efficiency limit of single-junction solar cells. The theoretical efficiency can reach about 43%, and there is still a lot of room for improvement in performance.
Stacked layers may be the most important form of perovskite commercial applications
A reporter from the Shanghai Securities News learned from the industry that compared to single-layer perovskite batteries, stacked perovskite batteries are considered by many companies to be a more promising product form in the future.
Fan Bin, chairman of GCL Optoelectronics, recently told a reporter from the Shanghai Securities News: "The mainstream form of perovskite products in the market will be laminates. It should be said that most perovskites will be applied in laminates."
Fan Bin said that GCL Optoelectronics is close to achieving the 18% node technology goal of single-layer perovskite cells. After that, the company will focus on researching crystalline silicon-perovskite stacked cell technology. GCL Optoelectronics plans to start commercial sales after achieving an efficiency of 26% for laminated modules.
Fan Bin analyzed that the current average efficiency of crystalline silicon modules is about 21%-22%, and the efficiency of the most efficient crystalline silicon modules available on the market is about 24%. When the efficiency of perovskite stacked components reaches 26%, it means that it can reach a level that cannot be reached by any crystalline silicon technology, and 26% is only the starting point for the efficiency of perovskite stacked components.
The Renshuo Lighting team led by Professor Tan Hairen has been included in many world records for laminated batteries. Renshuo Lighting adopts the same idea. The first step of industrialization is perovskite single-junction cells. After the single-junction cell technology matures, the second step is to upgrade to stacked cells. Renshuo Solar's newly built Changshu factory has taken into account the later production of laminated cells during planning.
In addition to leading startups, new energy giants also attach great importance to seizing the opportunity of perovskite and its stacked applications.
LONGi Green Energy recently announced that on November 3, the latest certification report from the U.S. National Renewable Energy Laboratory (NREL) showed that the efficiency of the crystalline silicon-perovskite stacked cell independently developed by LONGi Green Energy reached 33.9%, which is also the highest efficiency record for the world's crystalline silicon-perovskite stacked cell.
Guo Yongsheng of CATL’s 21CN Innovation Laboratory recently stated on CATL’s perovskite strategy that CATL’s long-term optimism and long-term investment in renewable energy is not just for the narrow theme of vehicle photovoltaics. Perovskite is a new topic for energy storage companies and vehicle OEMs.