Self-Assembled Hole Transporting Monolayer for Highly Efficient Perovskite Solar Cells

The unprecedented emergence of perovskite-based solar cells (PSCs) has been accompanied by an intensive search of suitable materials for charge-selective contacts. For the first time a hole-transporting self-assembled monolayer (SAM) as the dopant-free hole-selective contact in p-i-n PSCs is used and a power conversion efficiency of up to 17.8% with average fill factor close to 80% and undetectable parasitic absorption is demonstrated. SAM formation is achieved by simply immersing the substrate into a solution of a novel molecule V1036 that binds to the indium tin oxide surface due to its phosphonic anchoring group. The SAM and its modifications are further characterized by Fourier-transform infrared and vibrational sum-frequency generation spectroscopy. In addition, photoelectron spectroscopy in air is used for measuring the ionization potential of the studied SAMs. This novel approach is also suitable for achieving a conformal coverage of large-area and/or textured substrates with minimal material consumption and can potentially be extended to serve as a model system for substrate-based perovskite nucleation and passivation control. Further gains in efficiency can be expected upon SAM optimization by means of molecular and compositional engineering.