# Controlling Band-Bending for Perovskite Optoelectronic Devices Using Bismuth-Based Interlayers

## TL;DR

This paper shows how using bismuth-based interlayers can improve the performance of perovskite solar cells by adjusting energy levels at device interfaces.

## Contribution

The novel use of bismuth-based perovskitoids as interlayers to induce band bending in perovskite optoelectronic devices.

## Key findings

- Bismuth-based interlayers deepen the perovskite conduction band by approximately 0.5 eV.
- Solar cells with bismuth interlayers outperform those without when using C60 as the electron extraction layer.
- XPS and UPS measurements confirm the energy level alignment changes induced by the interlayer.

## Abstract

Interface engineering is a powerful tool for enhancing
electron/hole
transfer and extraction, as well as reducing charge carrier recombination
in perovskite-based optoelectronic devices, including light-emitting
diodes (LEDs) and photovoltaic (PV) devices. Here, incorporating an
interlayer between the perovskite and charge transport layers has
been an extremely successful approach to fine-tune energy level alignment,
boosting device performance. In this work, we investigate the incorporation
of bismuth-based perovskitoids as interlayers to deepen the position
of the perovskite’s conduction band. Our results clearly show
that perovskite solar cells based on a PIN architecture with a triple-cation
composition (TC) incorporating the bismuth-based interlayer outperform
those without when using C60-fullerene (C60)
as the electron charge extraction layer. We attribute this improvement
to the deepening of the conduction band position by approximately
0.5 eV, which agrees with the X-ray photoelectron spectroscopy (XPS)
and ultraviolet photoelectron spectroscopy (UPS) measurements. These
findings demonstrate the potential of Bi-based perovskitoid as interlayers
to induce band bending in the perovskite layer, effectively allowing
fine-tuning of the energy level alignment at the device interfaces,
thereby paving the way for future optoelectronic technologies.