Impact of interfacial binding between Au nanoclusters and TiO2 on solar cell performance

Abstract

Metal nanoclusters (NCs) hold great potential as photosensitizers owing to their discrete electronic transitions and atomic precision. However, a fundamental understanding of the interfacial dynamics governing NC adsorption onto TiO2, and its consequential impact on device performance, remains elusive. This study unveils a previously unrecognized interplay between chemisorption kinetics and charge recombination in metal nanocluster-sensitized solar cells (MCSSCs). We demonstrate that while pseudo-second-order chemisorption kinetics governs enhanced NC loading on TiO2, this process paradoxically induces an increase in surface trap state density, acting as recombination centers. In-depth open-circuit voltage decay analysis provides direct experimental evidence of the altered charge recombination dynamics arising from this chemisorption-induced defect generation. This counterintuitive phenomenon has a direct impact on power conversion efficiency, highlighting a critical trade-off between light harvesting and charge separation. Our findings further reveal that while the incorporation of sodium ions promotes NC loading, it concurrently exacerbates the formation of detrimental trap states and broadens the distribution of surface traps, thus increasing trap-mediated recombination. This newly discovered role of sodium ions in modulating surface defect density provides a novel insight into MCSSC performance optimization. These findings challenge the conventional understanding of NC sensitization and offer a critical new perspective on MCSSC design. © 2025 Elsevier B.V.