# Integrated Bulk–Surface Engineering Stabilizes MA‐Free Wide‐Bandgap Perovskites for Tandem Photovoltaics

## TL;DR

Researchers developed a new method to stabilize MA-free wide-bandgap perovskites, improving solar cell efficiency and stability for tandem photovoltaics.

## Contribution

A novel bulk–surface coupling strategy is introduced to stabilize MA-free wide-bandgap perovskites with high efficiency and long-term durability.

## Key findings

- MA-free wide-bandgap perovskite solar cells achieved 23.71% efficiency and over 1000 h of operational stability.
- Integrated tandem devices reached 32.26% efficiency with long-term durability.

## Abstract

Optimal wide‐bandgap perovskites are essential for perovskite/silicon tandem solar cells. Conventional wide‐bandgap perovskites, typically FA1‐

x

‐

y
Cs
x
MA
y
PbI1‐

z
Br
z
, contain volatile methylammonium (MA) components and mixed halides that compromise device stability and performance. Removing MA to form FA1‐

x
Cs
x
PbI1‐

z
Br
z
eliminates volatile organic components; however, the absence of MA and high Br content required for bandgap widening inevitably accelerates crystallization, increases defect density, and induces severe voltage losses. Here, we present a coupled bulk–surface regulation strategy that fundamentally overcomes these intrinsic bottlenecks. Incorporation of homopiperidinic acid hydroiodide into the precursor heals bulk lattice defects via ─COOH─Pb2+ coordination and suppresses halide migration through N─H…I– hydrogen bonding, while subsequent treatment with trimethylenediamine dihydroiodide salts neutralizes surface unsaturated Pb2+ and halide vacancies through amino‐Pb2+ coordination, hydrogen bonding, and electrostatic interactions. Their coupling effect precisely suppresses defect formation, minimizes non‐radiative recombination, and critically stabilizes halide distribution. As a result, the wide‐bandgap perovskite solar cells achieve an efficiency of 23.71% and enhanced operational stability with T92 exceeding 1000 h. Integrated into silicon tandem devices, they deliver 32.26% with long‐term durability. This work establishes molecular coupling consolidation as a new paradigm for constructing stable, high‐efficiency, MA‐free wide‐bandgap perovskites, advancing the practical realization of reliable tandem photovoltaics.

High‐bromide wide‐bandgap perovskites suffer from defects and phase segregation, limiting tandem performance. We report a bulk–surface coupling effect to heal lattice/surface defects and suppress halide migration. As a result, the wide‐bandgap device achieves 23.71% efficiency, while monolithic Si‐based tandems reach 32.26%, exhibiting exceptional long‐term operational stability.