Dual Functions of the Anchoring Groups in Self-Assembled Molecules as Effective Hole-Selective Contacts in Inverted Perovskite Solar Cells

Abstract

Self-assembled molecules (SAMs) have emerged as highly efficient hole-selective contacts in inverted perovskite solar cells (PSCs). Gaining insight into the role of individual molecular moieties is essential for the rational design of efficient SAMs. Herein, we systematically investigate four kinds of anchoring groups: carboxylic acid (-COOH), cyanoacetic acid (CN/COOH), phosphonic acid (-PO(OH)2) and cyano/cyano (CN/CN) in the EADR03 molecular framework to elucidate their roles on interfacial charge transfer. Our findings indicate that either carboxylic, cyanoacetic or phosphonic acid effectively binds to ITO, forming an ultra-thin layer. Interestingly, these anchoring groups passivate the buried interface, inducing high-quality perovskite films. Among them, the phosphonic acid-based derivative gives the highest efficiencies among all the anchoring groups tested, enabling 24.0% efficiency for 1.55 eV bandgap perovskite. In this work, we have carried out microscopic, photoluminescence and X-ray photoelectron spectroscopy studies at the ITO/SAM/perovskite interface, complemented with kinetic characterization on devices, to understand the dual functions of the anchoring groups of SAMs at two different interfaces, opening the path for further improvement in the innovative design of efficient molecules.