A KAUST-led team has developed a strategy to enhance the thermal stability of organic solar cells using nonfullerene acceptors.© 2023 KAUST; Heno Hwang.

Multicomponent mixtures could provide organic solar cells that defy heat and achieve record efficiency.

A strategy utilizing multicomponent mixtures of materials called nonfullerene acceptors boosts the thermal stability of organic solar cellsarticle. " id="return-reference-1" href="https://discovery.kaust.edu.sa/en/article/22997/k2028_best-thermal-stability-and-efficiency-in-organic-solar-cells/#reference-1">[1]. The approach developed by a KAUST-led team could make large-area organic photovoltaics easier to produce.

Nonfullerene acceptors (NFAs) have emerged as ideal components in organic photovoltaics, dramatically enhancing the device efficiency. The efficiencies of laboratory-scale devices and larger-area modules have improved rapidly over the last five years. Yet, when exposed to light and heat, NFA-based active layers become inherently unstable over time, which decreases device performance and hinders commercialization.

Organic solar cells rely on the active layer — a mixture of electron donor and acceptor molecules known as bulk heterojunction — to absorb light and produce electricity. When light strikes the heterojunction, it creates electron–hole pairs that dissociate at the donor–acceptor interface. Electrons move toward the acceptors while the positively charged holes move toward the donors. The resulting charge separation generates an electric current.

The heterojunction must have a specific nanostructure that is key for efficient charge separation and extraction. However, this nanostructure is often far from thermodynamic equilibrium, which causes it to change over time through the diffusion of the blend components. This diffusion promotes charge recombination, reducing device performance.

There are several approaches designed to enhance the thermal stability of organic solar cells, and most focus on exploiting molecular interactions or increasing the glass transition temperature. Bulk heterojunction blend films featuring NFAs with high glass transition temperatures can counteract long-range diffusion processes. However, short-range diffusion remains problematic.

Collaborator Christian Müller from Chalmers University of Technology in Sweden had shown that blending up to eight polycyclic aromatic hydrocarbons called perylenes produced mixtures that can yield a molecular glassarticle. " id="return-reference-2" href="https://discovery.kaust.edu.sa/en/article/22997/k2028_best-thermal-stability-and-efficiency-in-organic-solar-cells/#reference-2">[2]. This motivated the team led by Derya Baran and KAUST alumni Sri Paleti, now also at Chalmers, to explore the potential of acceptor mixtures containing more than two components for organic photovoltaics.

Read more at KAUST Insight.