Holistic design strategy of ferrocene-based interlayers for ultralow-noise perovskite photodetectors and high-efficiency solar cells.

Organometallic ferrocene (Fc)-based interlayers have emerged as effective interfacial modulators for next-generation perovskite optoelectronic devices. The thermally stable Fc core and reversible Fc/Fc+ redox couple, combined with carbonyl linkers, enable strong coordination to halide-related defects and tuneable frontier orbital energies, reducing non-radiative recombination and dark current in perovskite solar cells (PSCs) and perovskite photodetectors (PPDs), respectively. However, previous studies have focused on specific applications separately, resulting in a limited understanding of molecular design principles bridging device operating conditions. Here, we holistically investigate phenyl- and furyl-terminated ester- and ketone-linked Fc interlayers in PSCs and PPDs. By incorporating Fc-derivative interlayers, we demonstrate that the identity of the terminal group critically governs interfacial energetics and thereby directs device performance. Phenyl-based Fc interlayers generate a large potential step at the perovskite surface, as evidenced by a work-function (WF) shift. This creates a localized electrostatic barrier to reverse-biased hole injection, suppressing dark current density (J D) and enhancing the signal-to-noise ratio. In contrast, furyl-based analogs cause a negligible WF shift, leaving the interfacial injection barrier unperturbed. Instead, their illumination-induced band bending promotes balanced charge extraction while passivating surface traps. Electrochemical potential differences associated with ketone- and ester-linkers help explain the respective sub-trends, whereby the former enhance PPD performance, whilst the latter are preferred in photovoltaics. Consequently, PSCs modified with ferrocenyl-bis-furyl-2-carboxylate (F2) achieved state-of-the-art power conversion efficiencies (PCEs), reaching 26.51%, while PPDs modified with ferrocenyl-bis-phenyl-2-ketone (Ph1) attained outstanding specific detectivities, reaching 1.1 × 1013 Jones at -0.5 V (690 nm). These design guidelines highlight the broad applicability of organometallics in perovskite-based optoelectronic devices.