# Beyond Plasmonics: Au Nanoparticles as Electron Sinks in TiO2 for Interface Passivation Enhancement in Planar Perovskite Solar Cells

## TL;DR

This paper shows how embedding gold nanoparticles in a titanium dioxide layer improves the efficiency and stability of perovskite solar cells.

## Contribution

The study introduces a scalable method using sputtered Au nanoparticles in TiO2 to enhance interface passivation and charge selectivity in solar cells.

## Key findings

- Au nanoparticles embedded in TiO2 increase light-to-power conversion efficiency by 1.3%.
- Au nanoparticles passivate interface traps and modulate the interface potential through electron-sink behavior.
- High nanoparticle concentrations cause transport constrictions and increased resistance.

## Abstract

Improving the interface
passivation and charge selectivity
of electron
transport layers (ETLs) is essential to enhance both performance and
operational stability in perovskite solar cells (PSCs). In this work,
we introduce a sputtered double compact TiO2 ETL incorporating
monodisperse Au nanoparticles (NPs) as an electronically active interlayer.
The sputtering process ensures conformal encapsulation of the NPs
and precise control of TiO2 sublayer thickness, providing
a highly controlled platform to disentangle structural, optical, and
electronic effects of embedded metal NPs. This architecture enables,
for the first time, a systematic investigation of an electron-sink-induced
field-effect modulation of the AuNPs@TiO2/perovskite interface.
By precisely controlling NP size (15 and 55 nm), loading (0.15–1.20
wt %), and TiO2 encapsulation thickness (5–20 nm),
we identified an optimized architecture that delivers a 1.3% absolute
gain in light-to-power conversion efficiency, primarily through increased
short-circuit current density. Structural and optical analyses confirm
that NPs are uniformly embedded without modifying the TiO2 crystallinity and electronic structure. The results indicate that
embedded Au NPs may passivate interface traps and enhance ETL selectivity,
while their electron-sink behavior transiently captures charge and
modulates the interface potential. At high NP concentrations (>0.30
wt %), overlapping depletion regions lead to transport constrictions
and increased transport resistance. Furthermore, the Au NPs appear
to suppress the UV-driven photocatalytic activity of TiO2, improving device operational stability. These findings reveal a
new electron-sink mechanism in metal-oxide/metal-NP systems and establish
sputtered AuNPs@TiO2 ETLs as a scalable route toward more
selective and stable perovskite photovoltaics.