Insights from Impedance Spectroscopy in Perovskite Solar Cells with Self-Assembled Monolayers: Decoding SAM’s Tricks

Self-assembled monolayers (SAMs) are highly promising hole-transport layers for p-i-n perovskite solar cells, increasing photocurrent, reducing hysteresis and boosting photovoltage. However, the SAM's exact role in maintaining those benefits remains elusive. This work demonstrates that SAMs enhance open-circuit voltage (Voc) and stability by suppressing surface recombination, as revealed by impedance spectroscopy. This is reflected in the time constants related to ionic dynamics, taking values from 10–2 to 10–1 s for PTAA-based samples and 10–3 s for SAM devices. X-ray photoelectron spectroscopy shows that SAMs chemically bind with hydroxyl groups on metal oxide substrates such as indium tin oxide, reducing ionic accumulation and preventing ion-induced Voc losses. With minimal ionic dynamics, SAM-based devices achieve outstanding photovoltage and stability, confirming SAMs as pivotal in advancing perovskite cell performance.