Unintended Additive-Mediated Relocation of Self-Assembling Molecules Limits Charge Extraction in Sn–Pb-Based Perovskite Solar Cells

High Resolution Image Download MS PowerPoint Slide Self-assembling molecules (SAMs) are investigated as an alternative hole-transport layer to PEDOT:PSS for tin–lead (Sn–Pb) narrow-band gap (NBG) perovskite solar cells. Here we report on an unintended effect of the additive lead(II)-thiocyanate (Pb(SCN) 2 ) in SAM-based NBG perovskite solar cells. Upon an increase in the amount of Pb(SCN) 2, SAM-based layer stacks exhibit better film properties. Photoconversion efficiency reaches 18.5% for a concentration of 1% Pb(SCN) 2 and declines drastically for higher concentrations. Time-resolved photoluminescence and surface photovoltage measurements show that carrier extraction is impeded in Pb(SCN) 2 -containing layer stacks with >1% Pb(SCN) 2, and photoelectron spectroscopy reveals the unintended appearance of SAMs on the top surface of the perovskite layer. Relocated SAMs can be removed by solvent washing of the perovskite surface, recovering electron extraction but not the solar cell performance. This study highlights that commonly used additives must be adapted accordingly when introducing SAMs to NBG solar cells.