# Suppressing the Electron–Phonon Coupling in 2D Perovskite Cs3Sb2I9 for Lead‐Free Indoor Photovoltaics

## TL;DR

Researchers developed a new method to make lead-free perovskite solar cells that perform well under indoor lighting, achieving a record efficiency of 8.2%.

## Contribution

A chloride-free anion-exchange strategy was developed to suppress electron-phonon coupling in 2D perovskite materials, enabling high indoor photovoltaic performance.

## Key findings

- Anion-exchange strategy produced phase-pure Cs3Sb2I9 films with reduced Huang–Rhys factors and prolonged exciton lifetimes.
- Density functional theory confirmed weaker electron-phonon coupling in Cl-free structures compared to chloride-doped ones.
- The device achieved 8.2% power conversion efficiency under indoor lighting and 3.4% under solar illumination.

## Abstract

Antimony‐based perovskite‐inspired materials (Sb‐PIMs) are promising lead‐free candidates for indoor photovoltaic application. Cs3Sb2I9, in particular, with a ≈2.0 eV bandgap, is ideal for harvesting indoor white light. However, solution‐processed Sb‐PIMs preferentially crystallize into thermodynamically stable 0D structures, leading to strong self‐trapped exciton (STE) formation, limiting device performance. Although chloride (Cl) doping can induce 2D structural transitions, it enhances Fröhlich electron–phonon coupling (EPC), creating an intrinsic trade‐off. Here, we develop an anion‐exchange strategy to fabricate phase‐pure, Cl‐free 2D Cs3Sb2I9 films that suppress STE formation while enabling controlled dimensional reconstruction. This approach yields a reduced Huang–Rhys factor (from 30.7 to 21.5) and prolonged STE lifetime (8.60 to 9.19 ps). Density functional theory (DFT) calculations reveal a significant reduction in excited‐state octahedral distortion (Δd = 0.898 × 10−3 for Cs3Sb2I9 vs. 5.752 × 10−3 for Cs3Sb2I6Cl3), confirming intrinsically weaker EPC in Cl‐free structures. The device achieves a power conversion efficiency (PCE) of 3.40% under AM 1.5G solar illumination and an 8.2% PCE under 1000 lux white LED conditions. alongside Long‐term stability measurement confirms its environmental robustness. These results represent the highest indoor performance reported to date for Sb‐based perovskite‐inspired solar cells.

The study has developed an in situ anion‐exchange strategy to fabricate Pb‐free Sb‐based perovskite‐inspired materials (Sb‐PIMs) and solar cells, achieving a record indoor efficiency of 8.2% and a 3.4% power conversion efficiency under 1 sun illumination. Controlled structural dimensionality and suppressing Fröhlich electron–phonon coupling are realized through chloride‐free modulation, as evidenced by reduced Huang‐Rhys factors and DFT‐confirmed suppression of lattice distortions.