# One-Step Formation of 2D/3D Perovskite Heterojunction via Ligand Intercalation and Facet Engineering for Efficient Perovskite Solar Cells

## TL;DR

A new one-step method creates stable and efficient perovskite solar cells by forming 2D/3D heterojunctions with improved energy alignment and charge extraction.

## Contribution

A one-step in-situ fabrication method using oleylammonium ligands to form high-dimensional 2D/3D perovskite heterojunctions with enhanced stability and efficiency.

## Key findings

- Inverted perovskite solar cells achieved 26.22% efficiency for small areas and 21.1% for mini-modules.
- The method promotes (001) crystal orientation and higher-dimensional 2D phases (n ≥ 3) for better performance.
- Devices retained 90% efficiency after 1200 hours of photothermal testing and 80% after 1050 hours outdoors.

## Abstract

One-step in-situ incorporation of long-chain oleylammonium ligands enables simultaneous crystallographic orientation control and 2D/3D heterojunction formation in inverted perovskite solar cells.Facet engineering promotes dominant (001) orientation and higher-dimensional 2D phases (n ≥ 3) for improved energy alignment and charge extraction.Achieved power conversion efficiencies of 26.22% (0.1 cm2), 24.6% (1 cm2), and 21.1% (6.8 cm2 mini-modules) with excellent photothermal and outdoor stability.

One-step in-situ incorporation of long-chain oleylammonium ligands enables simultaneous crystallographic orientation control and 2D/3D heterojunction formation in inverted perovskite solar cells.

Facet engineering promotes dominant (001) orientation and higher-dimensional 2D phases (n ≥ 3) for improved energy alignment and charge extraction.

Achieved power conversion efficiencies of 26.22% (0.1 cm2), 24.6% (1 cm2), and 21.1% (6.8 cm2 mini-modules) with excellent photothermal and outdoor stability.

The online version contains supplementary material available at 10.1007/s40820-025-02058-8.

Two-dimensional/three-dimensional (2D/3D) perovskite heterojunctions at the contact interfaces have been proven to enhance the stability and power conversion efficiency (PCE) of perovskite solar cells (PSCs). The 2D/3D bilayer is typically formed via a solution post-treatment onto the 3D perovskite, where the 2D layer’s dimensionality depends on the ligand size and its reactivity. Despite their stability, long-chain ligands typically form 2D perovskites with low dimensionality (n = 1, 2) which feature poor charge conductivity and mobility. Here, we propose an in situ fabrication method incorporating long-chain oleylammonium (OlyA+) ligands directly into the perovskite ink. This approach forms 2D perovskite with higher dimensionalities (n ≥ 3) with enhanced (001) crystal facet orientation of the 3D film, improved energetic alignment, charge extraction, and structural stability. The fabricated inverted PSCs with 1.55 eV bandgap achieved a maximum PCE of 26.22% for small area and 24.6% for 1cm2 devices, as well as 21.1% for mini-modules (6.8 cm2). Additionally, the PSCs with in situ formed 2D/3D perovskite heterojunctions retained 90% and 80% of their initial PCE after 1200 h photothermal stability and 1050 h outdoor testing, respectively. Our one-step strategy produces uniform and stable 2D/3D perovskite heterojunctions with enhanced passivation capability, overcoming the limitations of conventional sequential methods and offering a promising and effective approach for highly stable and efficient PSCs.

The online version contains supplementary material available at 10.1007/s40820-025-02058-8.