Transitioning global energy production away from carbon-emitting sources toward renewable technologies is one of the foremost issues faced by the scientific community. Given the vast amount of solar energy incident on the planet, photovoltaic technologies will need to play a crucial role in decarbonization. To this end, metal halide perovskite solar cells (PSCs) have emerged as promising candidates for next-generation commercial photovoltaics, primarily thanks to the exceptional power conversion efficiencies (PCE) achieved (>27%).

Despite impressive performance improvements, several key challenges remain in the field of PSC, spanning both regular (n-i-p) and inverted (p-i-n) architectures, with further efficiency gains still achievable through interfacial and bulk defect management. Additionally, stability remains a key concern for the commercialization of this technology.

To address outstanding challenges in the field, an international multidisciplinary collaborative effort between Imperial College London and City University of Hong Kong has, during the past several years, spearheaded the development of highly tunable ferrocene-based organometallic compounds for PSC applications. The oral presentation proposed herein will focus on the directed compound design, from chemistry to device applications, of organometallic species for solar cell applications.

Our work on the n-type interface in inverted architectures began with a landmark paper in Science, exploiting a substituted ferrocene core (FcTc₂) to achieve record-breaking efficiencies and performance. This work was followed up by highly efficient and scalable multi-ferrocene Fc₂Tc₂ and Fc₃Tc₂ structures (JACS) and, more recently, by varying the side arms on the ferrocene core (Angewandte). This has allowed us to draw structure-function-efficiency relationships from the chemistry to the device application in these systems.

Recently, we have explored several new avenues exploiting the chemical tunability, electrochemical properties, and interchangeable oxidation states of ferrocene materials for applications in self-assembled monolayers, organic photovoltaics, and organic semiconductor doping, respectively. In n-i-p perovskite solar cells, convenient and highly tunable ferrocenium compounds were synthesized and employed as Spiro-OMeTAD dopants to achieve state-of-the-art power conversion efficiencies and stabilities (Joule, EES). Clear design guidelines for next-generation organic semiconductor dopants were drawn to inspire future development in the field. In lead-free tin-based perovskite solar cells, we developed a novel two-step on-surface self-assembled monolayer synthesis using conjugated molecular wire contacts. In organic solar cells, we exploited the redox-potential tunability of ferrocene centres to dope common n-type electron transport materials, clearly analysing the impact of ferrocene electrochemistry on performance, ultimately achieving power conversion efficiencies >20%.

In this talk, the story of organometallic compound development for solar cell applications will be outlined, and key translatable structure-property-performance relationships drawn from the wealth of work conducted will be provided.

Accepted Unpublished:

F. Vanin, .... Zonglong Zhu, Saif Haque, Nicholas J. Long, Joule, 2026

F. Fang, .... F. Vanin, Saif Haque, Maxie Roessler