Breakthrough in Ternary Organic Solar Cells: Matching the Efficiency of Conventional Solar Cells”

Scientists have recently made significant advancements in ternary organic solar cells (TOSCs), achieving efficiencies that rival conventional solar cells. This breakthrough was detailed in a recent publication in the journal Advanced Materials, and the research was conducted by scientists from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of the Chinese Academy of Sciences (CAS).

Organic vs. Inorganic Solar Cells

Organic photovoltaic solar cells (OSCs) utilize organic materials, such as small molecules or polymers, to convert sunlight into electricity. These differ from traditional inorganic solar cells, which employ crystalline silicon or other inorganic materials. OSCs offer several advantages, including flexibility, lightweight design, and the ability to be produced in flexible rolls rather than rigid panels using solution-based processes like inkjet printing. These characteristics make them suitable for various applications, such as sensors, portable chargers, or wearable electronics. OSCs can also be made semi-transparent or in various colors, allowing for aesthetic integration into buildings, windows, or other structures.

However, OSCs historically had lower power conversion efficiencies (PCE) compared to inorganic solar cells. TOSCs have helped address this issue by introducing a third component, often referred to as the “guest,” into the solar cell’s composition. This guest component plays a crucial role in optimizing the solar cell’s operation and improving its light-to-power conversion.

Role of the “Guest” Component

The guest component in TOSCs can broaden the spectrum of light absorption by selecting a material that absorbs light in a range not covered by the donor or acceptor components. This enhances overall sunlight absorption. Additionally, the guest component’s location within the solar cell can significantly affect its performance, as it can either transfer energy quickly or aid in capturing more sunlight, depending on its placement.

There are three possible locations for the guest component: embedded in the donor material, embedded in the acceptor material, or dispersed between the interface of donor and acceptor, forming blended, alloy-like structures (aggregations). Until recently, limited attention had been given to experimenting with the guest component’s location.

Experiment Details and Findings

In their study, the researchers used a guest component called LA1, which they modified with phenylalkyl side chains—a common functional group in the design of organic materials for photovoltaic devices. This modification improved LA1’s crystallinity and alignment while maintaining compatibility, enhancing its performance in TOSCs.

The researchers also controlled the distribution of the guest component by adjusting various conditions governing its interaction with the host components, including host/guest compatibility, surface energy, crystalline kinetics, and intermolecular interactions. This resulted in alloy-like aggregations within most of the guest molecules, which also permeated and dispersed into the host molecules.

Impressively, the size of these embedded host/guest “alloys” could be fine-tuned for improved electric charge transport and suppressed charge recombination. As a result, the researchers initially achieved PCE gains of over 15 percent. When combining their guest component with the Y6 family of acceptors as host components, they achieved even greater efficiency gains of over 19 percent.

While the researchers have achieved significant experimental success, they acknowledge that the theoretical understanding of the underlying mechanisms behind these gains is less well understood. Going forward, they aim to clarify these mechanisms further