Proceedings of Perovskite Thin Film Photovoltaics (ABXPV17)
Publication date: 18th December 2016
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 present an experimental study addressing 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 samples, and in particular the MAPI layer morphology, along the thickness. We find 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 influences also the phase transition of MAPI from tetragonal to orthorhombic, blocking MAPI at the tetragonal phase, regardless of the temperature. Graphene-based ETLs can therefore open the way to significant improvement of perovskite solar cells.