# Graphene-based electron transport layers in perovskite solar cells: a step-up for an efficient carrier collection

## TL;DR

This study demonstrates that graphene-based electron transport layers significantly enhance carrier collection efficiency and film quality in perovskite solar cells, leading to potential improvements in device performance.

## Contribution

The paper provides experimental evidence that graphene-doped ETLs improve carrier dynamics and film crystallinity in perovskite solar cells, advancing scalable fabrication methods.

## Key findings

- Carrier collection efficiency doubled with graphene-based ETL.
- MAPI layer shows lower trap density and better crystalline quality.
- Graphene ETL maintains MAPI in tetragonal phase regardless of temperature.

## Abstract

The electron transport layer (ETL) plays a fundamental role in perovskite solar cells. Recently, graphene-based ETLs have been proved to be good candidate for scalable fabrication processes and to achieve higher carrier injection with respect to most commonly used ETLs. In this work we experimentally study the effects of different graphene-based ETLs in sensitized MAPI solar cells. By means of time-integrated and picosecond time-resolved photoluminescence techniques, the carrier recombination dynamics in MAPI films embedded in different ETLs is investigated. Using graphene doped mesoporous TiO2 (G+mTiO2) with the addition of a lithium-neutralized graphene oxide (GO-Li) interlayer as ETL, we find that the carrier collection efficiency is increased by about a factor two with respect to standard mTiO2. Taking advantage of the absorption coefficient dispersion, we probe the MAPI layer morphology, along the thickness, finding that the MAPI embedded in the ETL composed by G+mTiO2 plus GO-Li brings to a very good crystalline quality of the MAPI layer with a trap density about one order of magnitude lower than that found with the other ETLs. In addition, this ETL freezes MAPI at the tetragonal phase, regardless of the temperature. Graphene-based ETLs can open the way to significant improvement of perovskite solar cells.