Dopant-Free HTL Enables 25.9% Efficiency in 2D/3D Perovskite Solar Cells

A global team led by the Massachusetts Institute of Technology (MIT) has made a landmark breakthrough in the development of 2D/3D perovskite solar cells, achieving both record efficiency and long-term stability. Published in Science, the study titled “Spontaneous Formation of Robust Two-Dimensional Perovskite Phases” introduces a new dopant-free hole transport layer (HTL) that enhances the reliability of the n-i-p device structure.

A Durable 2D Interlayer for Perovskite Stability

Traditionally, 2D perovskites serve as barrier layers to protect their 3D counterparts, but their fragility often compromises the overall durability of the cell. Lead author Shaun Tan explains that the team used a mixed-solvent method to develop a structurally robust 2D interlayer. This solution-processing technique enabled the formation of highly crystalline and pure 2D perovskites, critical to long-term performance in hybrid perovskite structures.

Eliminating Degradation Triggers

The researchers eliminated common degradation issues by avoiding unstable dopants in the HTL. Instead of traditional additives like tBP and LiTFSI, they used undoped spiro-OMeTAD. This dopant-free HTL enhances thermal stability while preserving device efficiency. The device stack includes:

• Fluorine-doped tin oxide (FTO)

• Chemical bath-deposited SnO₂ (CBD-SnO₂)

• 3D FAPbI₃ perovskite enhanced with MACl, MAPbBr₃, and excess PbI₂

• A pure 2D perovskite interlayer

• Spiro-MeOTAD

• Gold (Au) top electrode

This next-generation solar cell demonstrated a power conversion efficiency (PCE) of 25.9%, rivaling top-performing inverted p-i-n designs.

Long-Term Testing Validates Stability

Beyond raw performance, the devices withstood 1,074 hours of continuous illumination under 1-sun AM 1.5G conditions with UV exposure in a nitrogen environment, retaining 91% of their initial efficiency. This is a critical milestone for stable perovskite photovoltaics, especially for commercial applications that demand longevity.

Real-World Applications on the Horizon

Tan emphasized the wider implications of the study: “The combinatorial possibilities for 2D compositions and solvent blends are nearly infinite. This method could unlock new frontiers in perovskite solar cell efficiency and stability.”

A Global Collaborative Effort

This research reflects global collaboration among MIT, Sungkyunkwan University (South Korea), Marmara University (Turkey), Lawrence Berkeley National Laboratory, and the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL).