# Chemo-Strain Valence Engineering for Boosting Photovoltaic Response in Double Perovskite Epitaxial Films

## TL;DR

Researchers improved the photovoltaic performance of double perovskite films by using a substitution strategy that alters lattice and valence states, achieving record current density under white light.

## Contribution

A novel aliovalent substitution strategy synergizes chemical strain and defect engineering to enhance ferroelectric photovoltaic performance in double perovskite films.

## Key findings

- Pb substitution in Bi2FeMnO6 boosts short-circuit current density to 320 μA cm−2 under white light.
- The method increases JSC by 109-fold and VOC by fourfold compared to pure BFMO.
- Chemical strain and valence modulation are confirmed to enhance bandgap engineering and photovoltaic response.

## Abstract

A simple inequivalent substitution strategy modulates lattice distortion and
element valence states, realizing a remarkable boost in ferroelectric photovoltaic
performance under white light (|JSC| = 320 μA cm−2 after negative poling).Synergistic integration of chemical strain and defect engineering yields high performance ferroelectric photovoltaic in double perovskite thin films.Oxygen vacancies enable electric-field modulation of photovoltaic response in
ferroelectric thin films by tuning the band gap and engineering the Schottky
barrier.

A simple inequivalent substitution strategy modulates lattice distortion and
element valence states, realizing a remarkable boost in ferroelectric photovoltaic
performance under white light (|JSC| = 320 μA cm−2 after negative poling).

Synergistic integration of chemical strain and defect engineering yields high performance ferroelectric photovoltaic in double perovskite thin films.

Oxygen vacancies enable electric-field modulation of photovoltaic response in
ferroelectric thin films by tuning the band gap and engineering the Schottky
barrier.

The online version contains supplementary material available at 10.1007/s40820-026-02105-y.

Double perovskite films offer significant potential for multiferroic and ferroelectric photovoltaics due to their structural tunability. This study employs an aliovalent substitution strategy, partially replacing Bi with Pb in Bi2FeMnO6 (BFMO), to disrupt charge balance and local polarization while maintaining the host lattice. Pb incorporation simultaneously modulates the chemical states of all constituent elements, inducing pronounced lattice distortion and positive chemical strain. Unpoled Pb-BFMO films exhibit exceptional photovoltaic performance under 80 mW cm−2 illumination, achieving a short-circuit current density (|JSC|) of 192 μA cm−2 and an open-circuit voltage (|VOC|) of 0.525 V. This represents a 109-fold increase in intrinsic JSC and a fourfold enhancement in VOC compared to pure BFMO. The |JSC| demonstrates electric field tunability via polarization switching, reaching 320 μA cm−2 under negative polarization, the highest reported JSC for sub-100 nm single-layer ferroelectric films under white light. High-resolution high-angle annular dark-field scanning transmission electron microscopy, synchrotron-based reciprocal space mapping and X-ray absorption spectroscopy analyses collectively confirm the coupling of crystal distortion, chemical strain, and valence state alterations. The synergy between chemical strain and ionic valence states effectively engineers the bandgap and enhances photovoltaic response, which unlocks new application pathways for perovskite materials in optical memory devices and sustainable energy systems.

The online version contains supplementary material available at 10.1007/s40820-026-02105-y.