A team of researchers has designed a new electrode that could improve the stability of perovskite solar cells (PSC), the most promising candidate for the next generation of photovoltaic solar cells thanks to its low cost and high energy conversion efficiency.

This is because the insertion of a protective layer between the metal-based electrode and the perovskite film can prevent metal-induced degradation and graphene as such a layer can effectively suppress the diffusion of metals. and ionic ions.

This breakthrough was led by Professor Hyesung Park and his research team at the School of Energy and Chemical Engineering at UNIST. In their work, the research team developed a hybrid electrode platform based on a flexible metal grid, using a polyimide film (CEP) embedded in a copper grid with a graphene foil as a protective layer (GCEP ), exhibiting high electrical conductivity, an excellent chemical. stability and mechanical durability. The development demonstrates the critical role of graphene as a protective layer to prevent metal-induced degradation and halide diffusion between the electrode and the perovskite layer.

Graphene has high electrical conductivity, which allows electrons to easily move through it. However, the excellent impermeability of graphene prevents permeation of even the smallest molecule.

Graphene can be an effective diffusion barrier if combined with metal nanostructures which have excellent impermeability to diffusion of metals and halide ions at the metal electrode / perovskite layer interface, better charge collection at through the voids of metal nanostructures, minimal loss of optical transmittance as a protective layer due to its high optical transparency, and improved mechanical durability of the hybrid electrode.

The researchers used this transparent and flexible hybrid electrode to fabricate flexible metal PSCs based on TCE, achieving good chemical and mechanical stability. This device achieved a high PCE (16.4%), comparable to its rigid TCE-based counterpart (17.5%). They also verified the role of the graphene layer in ensuring the chemical stability of solar cells by avoiding the interdiffusion of metals and halide ions. In addition, the GCEP electrode improved the photostability of the PSC by blocking ultraviolet (UV) light and near UV light. It also maintained over 97.5% of the initial efficiency even after 1000 hours. Moreover, after 5000 bending tests, it showed excellent mechanical durability, such as maintaining 94% of the initial efficiency, and therefore was applicable to new generation user devices.

This work demonstrates that the insertion of a protective layer between the metal-based electrode and the perovskite film could prevent metal-induced degradation and that graphene, as such a layer, can effectively suppress the diffusion of metals and halide ions.

Gyujeong Jeong (Combined MS / Ph.D. Energy and Chemical Engineering Program, UNISt), first author of the study.

The new method has significantly improved both the efficiency and the stability of PSCs. This work provides an effective strategy to design mechanically and chemically robust, ITO-free, metal-assisted TCE platforms in PSCs.

Hyesung Park

More information: pubs.acs.org

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