The Power Conversion Efficiency Of Flexible Solar Cells Is Significantly Improved!

Recently, researchers at the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of the Chinese Academy of Sciences made improvements to the materials used in ternary organic solar cells (TOSC), achieving efficiency levels similar to traditional solar cells. This research was published in the journal "Advanced Materials." Organic photovoltaic solar cells (OSC) are a type of solar cell that converts sunlight into electricity using organic materials, typically small molecules or polymers, as opposed to traditional inorganic solar cells that use crystalline silicon or other inorganic materials.

One of the main advantages of organic solar cells is their versatility and lightweight nature. They can be produced at lower costs using solution-based techniques like inkjet printing, allowing for flexible rolls instead of rigid panels. As a result, they find applications in various fields such as sensors, portable chargers, and wearable electronic devices. OSCs can also be semi-transparent or colored, making them aesthetically pleasing and suitable for integration into buildings, windows, and other structures.

However, compared to inorganic solar cells, organic solar cells have lower power conversion efficiencies (PCE), which TOSC aims to improve. Standard binary organic solar cells consist of a donor material and an acceptor material, but TOSC is different as it includes a third component known as the "guest" material.

The inclusion of this guest component is crucial for enhancing various aspects of solar cell performance, such as altering the internal energy flux of the cell and optimizing how the cell converts light into electricity. The guest component is particularly important for increasing PCE, as it can broaden the spectrum of light that the solar cell can absorb. By selecting guest materials that absorb light in areas not covered by the donor or acceptor materials, the overall light absorption capacity of the cell can be improved. It also allows for fine-tuning the morphology of the mixed film, affecting exciton dissociation, charge generation, and transport.

Given that guest components can perform multiple different activities, their precise location within the solar cell "sandwich" or matrix significantly impacts performance. There are three possible positions for the guest component: embedded within the donor material, embedded within the acceptor material, or dispersed at the interface between the donor and acceptor, creating alloy-like mixed structures (aggregates). However, until recently, there has been relatively little experimental consideration of the guest component's position.

In their research, the scientists used a guest component called LA1 in TOSC, which differs from other guest component materials in terms of crystallinity. LA1 is a small molecule acceptor, and the researchers modified it with a phenylalkyl side chain, a functional group commonly used in organic materials for photovoltaic systems.

The modification of LA1 to include phenylalkyl side chains increased both crystallinity and alignment while maintaining sufficient compatibility, resulting in enhanced TOSC performance.

Additionally, the researchers controlled the distribution of the guest component by changing variables that influence the interaction between the host and guest components, such as host/guest compatibility, surface energy, crystalline kinetics, and intermolecular interactions. They found alloy-like aggregates in most guest molecules, which infiltrated and diffused throughout the entire host matrix.

The crystallite size of these integrated host/guest "alloys" could be easily tuned to enhance charge transfer and suppress charge recombination, resulting in an initial PCE increase of over 15%. Subsequently, by combining the guest component with Y6 series acceptors as the main component, they achieved an even greater efficiency boost of over 19%.

The researchers believe that they have achieved significant experimental success, but a better understanding of the underlying factors driving these advantages is needed in the future. They hope to gain a deeper insight into these fundamental systems.

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