Scavenger effect of Au NPs to stabilize the excess of TFSI− from Spiro-OMeTAD layer

Abstract

In this work, Au NPs were produced by laser ablation in liquids method (LASis) in isopropyl alcohol (IPA) and processed onto the Spiro-OMeTAD (hole transport layer,HTL) in perovskite solar cells. Spiro-OMeTAD requires the use of additives to improve its electrical features, and these additives include the hygroscopic LiTFSI to promote the oxidation of this HTL. AFM images pointed out that the TFSI− precipitates along the surface of Spiro-OMeTAD with the aging time, thus resulting in reduced stability for devices operating in the air. Therefore, to avoid this problem, two procedures were adopted: washing the surface of Spiro-OMeTAD with IPA or processing the Au NPs onto the surface of Spiro-OMeTAD from IPA suspension. Both procedures were performed by spin coating method prior to the deposition of the top electrode. The photovoltaic response showed that the devices produced with modified HTL presented superior stability mainly due to the removal of TFSI− precipitates from the surface of the Spiro-OMeTAD and the residual excess of TFSI− that can be chemically adsorbed onto the gold surface via oxygen atoms.