# The critical role of surface dipoles in CsPbI3 perovskite solar cells

## TL;DR

This paper shows that surface dipoles in CsPbI3 perovskite solar cells significantly impact performance and stability, with efficiency increasing from 10% to 20%.

## Contribution

The study reveals that surface dipoles formed by modifying surface stoichiometry strongly influence device performance and stability.

## Key findings

- Modifying the Cs:Pb ratio in the top 1 nm of CsPbI3 creates surface dipoles that alter the work function by over 2 eV.
- Surface dipoles increase power conversion efficiency from below 10% to ∼20%.
- High-performing devices with strong dipoles degrade more rapidly, affecting stability.

## Abstract

Interfacial modification is a key strategy for improving the performance of perovskite photovoltaic devices. However, most commonly, improvements in device performance through surface treatments of the perovskite active layer are attributed to defect passivation. At the same time, such treatments may also lead to the formation of a dipole at the surface of the perovskite active layer. In this work, we demonstrate that treatments that modify the surface stoichiometry of CsPbI3 perovskites can lead to effective defect passivation, yet result in the formation of surface dipoles of opposing directions that modulate the work function of CsPbI3 over a range of more than 2 eV. Such dipoles influence the built-in potential of the devices and the efficiency of interfacial charge transfer in CsPbI3 solar cells, resulting in power conversion efficiencies that increase from below 10% to ∼20% depending on the surface dipole. The surface stoichiometry also has a strong influence on device stability, where initially high-performing devices are found to be prone to a more rapid degradation. These results highlight that the formation of surface dipoles plays a crucial role in impacting the performance and stability of CsPbI3 solar cells, making the choice of device architecture particularly important.

Finely modulating the Cs : Pb ratio of the top 1 nm of CsPbI3 leads to strong surface dipoles that alter the work function by more than 2 eV, increasing the power conversion efficiency from ∼10% to ∼20% and critically affecting stability.