Work Function Tuning through Self-Assembling Monolayers of Fluorinated Molecules
Laura Canil a, Antonio Abate a b
a Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, Berlin, Germany
b University of Naples Federico II, Corso Umberto I 40, Naples, Italy
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#PERFuDe19. Halide perovskites: when theory meets experiment from fundamentals to devices
Berlin, Germany, 2019 November 3rd - 8th
Organizers: Claudine Katan, Wolfgang Tress and Simone Meloni
Oral, Laura Canil, presentation 328
Publication date: 18th July 2019

With a power conversion efficiency over 24%, perovskite solar cells (PSCs) are considered a rising star in the solar energy. Nowadays a lot of research is focused on the improvement of the device performance through the employment of new materials or architectures [1,2]. With regard to this, the importance of interfaces in such a system is well known and in particular a crucial role is played by the energy level alignment of the different layers [3].

A good match between the electronic bands is required in order to obtain high performance PSCs structures, to this purpose we functionalize the interface between the perovskite and the charge selective contacts within the device. We make use of specific molecule-to-substrate interactions to self-assembly perfluorinated small molecules on the perovskite surface. This results in the formation of an interfacial dipole and leads to a shift in the perovskite work function, which allows us to tune the perovskite energy levels and therefore be flexible in the choice of the transport layers. Our results show that with this technique even materials with a non optimal energy level alignment can lead to device performances comparable with the state of art.

Moreover, the formation of a nanometer thick perfluorinated layer results in hydrophobicity of the perovskite surface, which enhances stability by preventing the ingress of water from the atmosphere.

Notably, such a functionalization can be done through scalable solution processing methods, which are compatible with fast output production including roll-to-roll and inject printing. We investigate the impact of the functionalization on material and device by characterizing the change in the energetics of the system and correlating them with the PSCs performance.

The interface functionalization with perfluorinated molecules is an effective new approach to improve energy levels alignment and enhance PSCs performance. This technique can be used as a universal tool to tune the work function and control its shift, which leads to more flexibility in the choice of materials and structure.

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