Perovskite photocatalysis: realizing long-lived charge-separated states at the interface of CsPbBr3 nanocrystals and functionalized ferrocene molecules

Abstract

Cesium lead halide (CsPbX₃) perovskites, having stood out for solar cell applications, are now garnering attention in the field of photocatalysis as well. With a fundamental challenge in photocatalysis of timely charge carrier extraction before recombination, incorporating ferrocene (Fc)-based functionalities can offer remarkable charge extraction efficiency in lead halide perovskites, given a recent 25% power conversion efficiency in a solar cell developed with a similar approach. Here, we have covalently linked Fc with amino acid residues to design three molecular redox relays differing in the ratio of –COOH to Fc units and employed them to probe the hole transfer dynamics in CsPbBr₃ perovskite nanocrystals (NCs) for photocatalytic applications. With Fc forming a part of the hydrophobic tail, the presence of the polar carboxylic acid (–COOH) headgroup endowed the molecule with a surfactant-type nature so that it could bind to the CsPbBr₃ NCs' surface in colloidal solution. Interestingly, the enhanced binding in all three cases, as evident by the XPS peak shift, led to the formation of a long-lived charge-separated state when a dipole was created between the electrons in CsPbBr₃ and holes in surface-bound Fc derivatives. This was evident in the transient absorption spectra when an unusually sustained bleach of the CsPbBr₃ excitonic peak was observed in the presence of Fc derivatives. Such prolonged existence of the charge-separated state undoubtedly reflects upon the utility of molecular systems as cost-effective as Fc derivatives in perovskite NCs to carry out photocatalytic reactions where timely extraction of charge carriers is always a challenge to overcome.