# Shallow-level defect passivation by 6H perovskite polytype for highly efficient and stable perovskite solar cells

## TL;DR

A new approach using 6H polytype perovskite reduces defects and improves efficiency and stability of perovskite solar cells.

## Contribution

The study introduces 6H polytype perovskite to passivate defects and enhance solar cell performance.

## Key findings

- 6H polytype perovskite reduces iodide vacancy defects in FAPbI3, improving carrier dynamics.
- Surface passivation of hetero-polytypic films achieves ultra-long carrier lifetimes and high power conversion efficiencies.
- Modules with this configuration show long-term stability and high certified efficiency.

## Abstract

The power conversion efficiency of perovskite solar cells continues to increase. However, defects in perovskite materials are detrimental to their carrier dynamics and structural stability, ultimately limiting the photovoltaic characteristics and stability of perovskite solar cells. Herein, we report that 6H polytype perovskite effectively engineers defects at the interface with cubic polytype FAPbI3, which facilitates radiative recombination and improves the stability of the polycrystalline film. We particularly show the detrimental effects of shallow-level defect that originates from the formation of the most dominant iodide vacancy (VI+) in FAPbI3. Furthermore, additional surface passivation on top of the hetero-polytypic perovskite film results in an ultra-long carrier lifetime exceeding 18 μs, affords power conversion efficiencies of 24.13% for perovskite solar cells, 21.92% (certified power conversion efficiency: 21.44%) for a module, and long-term stability. The hetero-polytypic perovskite configuration may be considered as close to the ideal polycrystalline structure in terms of charge carrier dynamics and stability.

Defects in perovskite materials are detrimental to their carrier dynamics and structural stability. Here, the authors incorporate 6H polytype perovskite into bulk to reduce defects and improve structural integrity, realizing efficient solar cells and modules with long-term stability.