# A tin fluoride-free, efficient and durable tin-lead perovskite solar cell

## TL;DR

This paper presents a new method to improve the stability and efficiency of tin-lead perovskite solar cells by replacing tin fluoride with lead-based additives.

## Contribution

A novel strategy using lead powder and PbF2 post-treatment replaces SnF2, enhancing both efficiency and stability in tin-lead perovskite solar cells.

## Key findings

- Replacing SnF2 with lead-based additives increases device efficiency from 16.43% to 24.07%.
- The new method prevents hydrofluoric acid release and electrode corrosion during photo-thermal treatments.
- The cells retain 60% of their initial efficiency after 550 hours at 85°C under maximum power point.

## Abstract

The photo-thermal stability of tin-lead perovskite solar cells remains a major challenge. SnF2 is commonly used to inhibit Sn2+ oxidation and reduce hole density, however, the stability of devices remains poor. Here, we found that the poor stability partially results from an adverse effect of SnF2, which reacts with formamidine iodide during photo-thermal treatments. This reaction leads to degradation of perovskite and release of hydrofluoric acid, which corrodes electrodes. To address this issue, we develop a strategy that combines lead powder in precursor with PbF2 post-treatment, replacing the role of SnF2 as in film formation and surface defect passivation, respectively. The d-electron polarization in Pb2+ strengthens its bond with F⁻, making it react inert to perovskite. In this work, the efficiency of SnF2-free devices increases from 16.43% to 24.07%. The cells retain 60% of their initial efficiency after 550 hours operating at 85 °C under maximum power point.

Achieving photo-thermal stability and device operational stability of tin-lead perovskite solar cells remains a major challenge. Here, authors replace tin fluoride additive by lead powders followed by lead fluoride post-treatment, achieving efficiency of 24.07% in stable tin fluoride-free devices.