Work Function Tuning through Self-Assembling Monolayers of Fluorinated Molecules
Laura Canil a, Thomas Dittrich a, Antonio Abate a b
a Helmholtz-Zentrum Berlin für Materialien und Energie, Kekuléstraße 5, 12489 Berlin, Germany
b University of Naples Federico II, Corso Umberto I 40, Naples, Italy
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Laura Canil, 215
Publication date: 11th February 2019

With a power conversion efficiency over 23%, 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, but this is always challenging, especially when new materials are explored. 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 leads to passivation and reduction of recombination, but most importantly induces a shift in the perovskite work function which can reduce the bands offset. Moreover it allows us to be flexible in the choice of the charge transport layers and consequently to explore new stable and cheap materials. Beside this, 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 changes in the energetics of the system and correlating them with the PSCs performance.

Our results show that the interface functionalization with perfluorinated molecules is an effective new approach to improve the energy levels alignment and enhance PSCs performance, by allowing us to be flexible in the choice of materials and structure.

© Fundació Scito
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