Add a bit of spice to the perovskite battery, it becomes more efficient | Joule

source：beike new material Views：6278time：2021-01-22 QQ Academic Group: 1092348845

In order to make perovskite solar cells more efficient, the scientists added capsaicin to the perovskite.

Capsaicin perovskite solar cell. Image source: Jin Yang

Written by Wei Xiao

Scientists in China and Sweden have discovered that capsaicin may be the "secret recipe" for making perovskite solar cells more stable and efficient. This new study, published in Joule on January 13th, shows that adding capsaicin to the precursor of perovskite-type methylammonium lead triiodide (MAPbI3) during the preparation process can cause a large amount of electrons. Enrichment, a larger current is generated on the surface of this semiconductor material, resulting in a polycrystalline MAPbI3 solar cell with the highest charge transfer efficiency so far.

Spice up the perovskite
As a new technology leading the current clean energy boom, perovskite solar cells have been developing rapidly for nearly a decade. In 2011, the first perovskite solar cell with a light energy conversion efficiency exceeding 10% was born in the Clarendon Laboratory at Oxford University. Today, the most advanced perovskite semiconductor materials have already doubled the above-mentioned light energy conversion efficiency. Low manufacturing cost, high-quality crystal structure, and lightweight and soft material characteristics make perovskites favored by the academic and industrial circles. However, as a clean energy technology, perovskite solar cells still have many obstacles on the way to enter the global photovoltaic market. How to reduce energy consumption caused by poor materials, improve stability, and ensure that equipment is green, safe and pollution-free is an urgent need Technical issues resolved.

The core component of a perovskite solar cell is a thin film formed of perovskite semiconductor. When sunlight shines, some electrons in the perovskite material absorb energy and break away from the atomic bond. Excited electrons full of energy move sideways through the crystal lattice in the material, either escape from one end of the battery, and then quickly transfer away as a useful current by the electrode, or encounter an obstacle or trap, which loses energy and releases Useless heat. Therefore, the more crystal defects of the material, the greater the obstruction of electron flow, and the lower the light energy conversion efficiency of the battery. Metal halide perovskite semiconductor is a very promising core component in the current frontier technology of solar cells, but this type of material has an undesirable phenomenon at the electronic level, which is called non-radiation recombination, which will reduce the efficiency of the battery and aggravate it. Heat loss.

In this paper published on January 13, Bao Qinye, a professor in the School of Physics and Electronic Science of East China Normal University, and his colleagues found a way to change the electronic structure of the perovskite semiconductor surface area and reduce the energy loss of the device-giving calcium Titanium ore is "a little spicy". The researchers told the "research circle" that they have been looking for simple and effective additives, hoping to use green and sustainable biological addition technology, combined with non-toxic lead-free perovskite semiconductors, to develop higher-performance, completely green calcium Titanium ore solar cells. At this time, capsaicin appeared.

Capsaicin is derived from the active ingredient of pepper, and it is also the source of spicy and stimulating flavor for food. However, in the eyes of materials physicists, it is still a natural forest-based biological material, suitable for large-scale production of high-efficiency perovskite solar cells in the future. This type of material has the ability to passivate defects in the perovskite and adjust the interface energy level, thereby improving the efficiency and stability of the perovskite solar cell.

Image source: Pixabay

The researchers comprehensively considered the electrical, chemical, optical, and stability properties of capsaicin, and believe that it is likely to be an additive that can reduce the crystal defect density of perovskite films and avoid the loss of efficiency caused by non-radiation recombination.

In order to test the actual effect of capsaicin, the research team added 0.1% (mass ratio) of capsaicin to the MAPbI3 perovskite precursor, which was the best concentration found in the test, and then used this "spicy" material to make solar energy battery. Next, the researchers applied a series of technologies such as ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and time-resolved photoluminescence to detect how the added capsaicin would affect the performance of solar cells.

They found that the light energy conversion efficiency of the control battery equipment was 19.1%, while the capsaicin-added battery equipment was 21.88%, almost as high as the 21.93% record of the single crystal MAPbI3 device. In addition, this capsaicin solar cell also shows higher stability. After being placed in the environment for 800 hours, the efficiency can still be maintained above 90% of its initial value.

The researchers also found that capsaicin can greatly reduce the defect density of perovskite films, increase electron density by an order of magnitude, and promote charge transport. In addition, they observed a small leakage current in the capsaicin-added solar cell, indicating that the compound successfully inhibited radiation-free recombination.

The researchers explained that capsaicin is effective because it forms an interface between the p-type semiconductor layer and the n-type semiconductor layer by changing the surface energy of the perovskite material. Since the p-type semiconductor layer contains more "holes" than electrons, and the n-type semiconductor layer contains more electrons than "holes", the interface formed by capsaicin can promote charge transport and suppress the efficiency that occurs in traditional perovskite semiconductors loss.

The green, non-toxic and sustainable capsaicin is very suitable as an additive to combine with non-toxic lead-free perovskite semiconductors to improve the safety and stability of perovskite solar cells. This is also the future of perovskite solar cells to achieve a wide range of applications An important part of But at the same time, the researchers also pointed out that the effect of capsaicin on non-toxic, lead-free perovskites (such as inorganic perovskites and double perovskites) still needs more in-depth research. Before being put into commercial application, the stability of this new material must also be further improved.

Not only pepper, but also coffee
In fact, it is not the first time that biomaterials are used as "boosters" for perovskite solar cells. In April 2019, Professor Yang Yang from the School of Materials Science and Engineering at the University of California, Los Angeles and his colleagues found that caffeine can significantly improve the thermal stability of perovskite solar cells and increase the efficiency of solar cells from 17% to 20%. %.

The inspiration for this research came from the daily life of two doctoral students in the Yang Yang group-drinking coffee and discussing perovskite research: Since people need coffee to refresh themselves, is the same with perovskite? The answer is yes.

Caffeine is a common alkaloid. Its carbonyl group can form a molecular lock with the lead ion of the perovskite, which can improve the stability of the perovskite. At the same time, such molecular locks can reduce the nucleation rate of perovskite crystals, obtain higher-quality perovskite polycrystalline films, and can make the perovskite grains more oriented, thereby increasing the electrons in the material lattice In order to improve the photoelectric conversion efficiency of perovskite solar cells.

In the next experiment, Yang Yangs research group added caffeine to the perovskite layer of 40 solar cells. Under the confirmation of infrared absorption spectroscopy, they found that caffeine can successfully combine with perovskite. In further transmission electron microscopy tests, the molecular lock remained stable when the "coffee drunk" perovskite material was heated by the electron beam, and the output power of the solar cell was increased by about one-fifth.

"Caffeine" perovskite solar cell from the University of California, Los Angeles. Image source: Jingjing Xue | Scientific American

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If it is said that "drinking coffee" for perovskite comes from an Eureka moment that fell from the sky, then "adding spice" for perovskite is closer to a prepared plan.

The researchers of this new paper said that they will pay more attention to the chemical structure of natural forest-based biomaterials such as capsaicin and lignin, as well as their interaction with photosensitive materials and corresponding photovoltaic properties. In the future, green and sustainable biomaterial addition technology will become an obvious trend for non-toxic lead-free perovskite materials. Obtaining a completely green and environmentally friendly perovskite solar cell that can be used as a clean energy source is their ultimate hope.

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Paper Information
【Title】Direct Observation on p- to n-Type Transformation of Perovskite Surface Region during Defect Passivation Driving High Photovoltaic Efficiency.

【Author】Shaobing Xiong, Zhangyu Hou, Shijie Zou, Xiaoshuang Lu, Jianming Yang, Tianyu Hao, Zihao Zhou, Jianhua Xu, Yihan Zeng, Wei Xiao, Wei Dong, Danqin Li, Xiang Wang, Zhigao Hu, Lin Sun, Yuning Wu , Xianjie Liu, Liming Ding, Zhenrong Sun, Mats Fahlman, Qinye Bao

【Journal】Joule

【Date】January 13, 2021

[DOI] https://doi.org/10.1016/j.joule.2020.12.009

【Summary】

Perovskite solar cells (PSCs) suffer from significant nonradiative recombination, limiting their power conversion efficiencies. Here, for the first time, we directly observe a complete transformation of perovskite MAPbI 3 surface region energetics from p- to n-type during defect passivation caused by natural additive capsaicin, attributed to the spontaneous formation of a pn homojunction in perovskite active layer. We demonstrate that the pn homojunction locates at ～100 nm below perovskite surface. The energetics transformation and defect passivation promote charge transport in bulk perovskite layer and at perovskite/ PCBM interface, suppressing both defect-assisted recombination and interface carrier recombination. As a result, an efficiency of 21.88% and a fill factor of 83.81% with excellent device stability are achieved, both values are the highest records for polycrystalline MAPbI 3 based pin PSCs reported to date. The proposed new concept of synergetic defect passivation and e nergetic modification via additive provides a huge potential for further improvement of PSC performance.

【link】

https://www.cell.com/joule/fulltext/S2542-4351(20)30608-5

Reference materials:

1.https://www.eurekalert.org/pub_releases/2021-01/cp-tct010721.php

2.https://www.scientificamerican.com/article/caffeine-peps-up-solar-energy/

3.Caffeine Improves the Performance and Thermal Stability of Perovskite Solar Cells. Wang, Rui et al. Joule, Volume 3, Issue 6, 1464 – 1477

https://www.cell.com/joule/fulltext/S2542-4351(19)30173-4

4. "Global Science" 2015, Issue 8 "Perovskite: the new favorite of solar cells"

4.https://mp.weixin.qq.com/s/ZniMhK4zLsKxv0D720eKOw

Source of Information: Research Circle

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