Pack "cartilage" for perovskite solar cells

Hu Xiaotian (second from right) and team members are doing experiments.

In recent years, perovskite solar cells have unique advantages and huge application potential in flexible wearable electronic devices. However, perovskite is a "hard bone", and its brittleness, crystallinity and other characteristics affect the further development and commercial expansion of its "flexible" application.

In order to make perovskite solar cells more "gentle", Song Yanlin, a researcher at the Institute of Chemistry of the Chinese Academy of Sciences, Chen Yiwang, a professor at Jiangxi Normal University, and Hu Xiaotian, a researcher at Nanchang University, started a joint research. Recently, researchers have been inspired by the rigid spine bone crystal and flexible structure to develop a conductive adhesive polymer interface layer, through bionic grain boundaries and structural design, to achieve large-area flexible perovskite solar cell printing preparation. Related research results have been published in "Nature-Communication".

Believe in your "gentle" nature

The organometallic halide semiconductor in perovskite has light-absorbing properties, and the researchers were inspired by this to develop a perovskite solar cell. Perovskite solar cells have the technological characteristics of low-temperature solution processing and large-area printing preparation, and are recognized as photosensitive materials that are expected to be used in lightweight and flexible photovoltaic devices.

However, the road from "performing stone to gold" for perovskite batteries is not smooth. Perovskite materials and indium tin oxide transparent electrodes are inherently brittle and have poor bending resistance and other mechanical structural design issues, which hinders their application.

Hu Xiaotian told China Science News that the mechanical stability of flexible perovskite solar cells is poor. Perovskite, as a crystalline material, is prone to cracks under stress, which in turn affects device performance. At the same time, flexible perovskite solar cells are "sensitive". Perovskite materials are sensitive to water and oxygen, and are prone to degradation under the working conditions of oxygen and water.

In addition to stability, Song Yanlin believes that at this stage, the large-area printing process based on high-quality perovskite films is not yet mature, and detailed analysis and precise control of the nucleation and crystallization process during the preparation of perovskite films are required. Large-scale preparation of mining devices has a long way to go."

Faced with preparation difficulties, Hu Xiaotian still believes in its potential. "Our research work has always aimed at wearable solar cells, with proper modification, packaging and mechanical structure design."

In this regard, Chen Yiwang and Hu Xiaotian have the same firm belief. "I think the biggest advantage of perovskite solar cells is the potential for application in flexible devices. Although perovskite solar cells have not yet been commercialized, the device efficiency and stability that have been broken through year by year give us confidence and continued research. Courage." Chen Yiwang said.

With the same belief, the research team experimented with multiple methods, but they never achieved the desired results.

Bend over for inspiration

At a time when research is in vain, Hu Xiaotian noticed the wonderful spine skeleton. The spine bone is also a "hard bone", but it is flexible and can be bent repeatedly. Its flexible structure is a combination of "hard-soft-hard" materials, and its growth is generally based on the nucleation and crystallization process of hydrophobic cartilage.

Based on this, the research team thought of designing a viscous hydrophobic interface layer similar to spinal cartilage, synergistically regulating the crystalline quality and bending resistance of perovskite crystals from the aspects of crystalline bionics and structural bionics, thereby realizing large-scale flexible perovskite Printing and preparation of mine solar cells.

After repeated experiments, the researchers synthesized a hydrophobic viscous conductive polymer and used it as an interface layer between the transparent electrode of indium tin oxide and the perovskite layer of the perovskite solar cell, successfully in two "hard bones" Introduce a piece of "cartilage".

Under the escort of this "cartilage", the researchers realized the printing and preparation of high-efficiency large-area flexible perovskite devices in the laboratory, and verified the feasibility of its practical application in low-power devices. This structural design, while ensuring sufficient device power conversion efficiency, also exhibits excellent mechanical stability.

Chen Yiwang introduced that the biggest feature of this conductive viscous polymer is the regulation of the perovskite crystallization process and the optimization of the bending resistance structure of the device. Through the interaction of the interface hydrophobicity and the interface layer itself with the perovskite ink, the control is adjusted to Nucleation sites in the membrane process, and thus realize the preparation of large-size, high-quality perovskite thin films. At the same time, with the help of the stress absorption and release of the interface layer during bending, the overall mechanical stability of the device is optimized.

How to measure actual effect? Chen Yiwang said that in the past, judgments were often made with the naked eye. For example, the mechanical explanation for the improvement of the bending resistance of flexible devices based on the hydrophobic adhesive interface layer, and the optimization of the bending resistance were demonstrated by the morphological characterization after multiple bending. "This kind of interpretation angle is too general and vague, and it's just looking at pictures and talking, and it doesn't have a significant reference." Chen Yiwang said.

He believes that in the context of large-scale optimization of mechanical stability, a reasonable explanation of the effect is necessary. To this end, the researchers read a lot of literature, and consulted experts in related fields, and finally concluded a set of calculation system for the mechanical mismatch coefficient of flexible perovskite devices based on Young's modulus. This method combined with finite element simulation to explain and explain the root of the device's mechanical stability more deeply.

"After experiencing this kind of research process, my biggest insight is that scientific research should learn to cross disciplines. Many of the key scientific issues in my own research direction can often get inspiration and help from research results in other fields. This process may be boring and tedious. But the research results obtained are generally interesting and have significant scientific significance." Chen Yiwang said.

Aim to wear

Talking about the innovation of this research, Hu Xiaotian summarized three words-bigger, higher, and more bend-resistant, that is, the large-area printing preparation of perovskite devices is realized, and the power conversion efficiency and flexibility of flexible devices are refreshed. The device can be bent 7000 times under the limit bending radius.

It is worth mentioning that the perovskite battery can still maintain an initial efficiency of more than 85% after 7000 cycles of limit bending radius. At present, in terms of device power conversion efficiency, the research results have been certified by relevant certification bodies.

"Our ultimate goal is to achieve large-scale printing preparation and practical application of flexible wearable solar cells." Hu Xiaotian said.

How exactly do flexible perovskite devices affect human life? Chen Yiwang painted a picture of application. With the help of flexible low-power devices such as flexible perovskite batteries, mobile phones, watches, etc., it can realize the power storage function at any time during use; at the same time, based on the light-weight characteristics of perovskite devices, it can be developed. Wearable mobile power supply that fits with skin or clothing to avoid the trouble and embarrassment caused by the insufficient power of various mobile devices...

Chen Yiwang said that unlike rigid and heavy crystalline silicon solar cells, flexible perovskite devices can bring convenience to people's lives without affecting the normal activities of the human body.

The study is not over. Hu Xiaotian said that the research team will continue to research and develop new types of flexible device structures, and through more in-depth exploration and mining, master the large-area and high-efficiency printing process of flexible devices, with larger size, higher efficiency and better stability. Flexible perovskite devices. At the same time, considering the skin affinity during actual use, some research and attempts will be made on the tensile and torsion resistance of flexible devices. (â– Reporter Bu Ye)

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