Investigating photoelectrode interfaces is challenging due to complex charge carrier pathways, and photodegradation aggravates this difficulty because interfacial properties are significantly altered by degradation. Unlike dyes and semiconductors that degrade into photoinactive materials, the photodegradation of Au nanoclusters (NCs) yields Au nanoparticles (NPs) that are photoactive. Besides, these NPs can form Schottky barriers with TiO2, which can affect interfacial band structures. Hence, the copresence of this photoactive nanoduo gives rise to unprecedented complexity in understanding the photoelectrochemical behavior of NC-sensitized photoelectrodes. In this work, we unveil that electron injection into TiO2 and subsequent electron trapping at deep surface trap states in TiO2, which are created by sensitization, play a vital role in the photodegradation. We also demonstrate that photocurrent can be enhanced through judicious control over photodegradation that would otherwise be deleterious. This photocurrent enhancement is attributed to multiple overlooked effects of Au NPs (plasmonic field enhancement and interfacial band bending).

Intrinsic low stability and short excited lifetimes associated with Ag nanoclusters (NCs) are major hurdles that have prevented the full utilization of the many advantages of Ag NCs over their longtime contender, Au NCs, in light energy conversion systems. In this report, we diagnosed the problems of conventional thiolated Ag NCs used for solar cell applications and developed a new synthesis route to form aggregation-induced emission (AIE)type Ag NCs that can significantly overcome these limitations. A series of Ag(0)/Ag(I)-thiolate core/shell-structured NCs with different core sizes were explored for photoelectrodes, and the nature of the two important interfacial events occurring in Ag NCsensitized solar cells (photoinduced electron transfer and charge recombination) were unveiled by in-depth spectroscopic and electrochemical analyses. This work reveals that the subtle interplay between the light absorbing capability, charge separation dynamics, and charge recombination kinetics in the photoelectrode dictates the solar cell performance. In addition, we demonstrate significant improvement in the photocurrent stability and light conversion efficiency that have not been achieved previously. Our comprehensive understanding of the critical parameters that limit the light conversion efficiency lays a foundation on which new principles for designing Ag NCs for efficient light energy conversion can be built.

Optoelectronic properties of Au18(SR)14 are modulated by Ag doping, and its influence on photoelectrochemical performance is investigated. The best compromise for light conversion efficiency is made when a single Ag atom is incorporated.