4-Hydroxy-2,2,6,6-tetramethylpiperidine as a Bifunctional Interface Modifier for High-Efficiency and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) have made great research progress in the past decade. The interface behavior between the perovskite active layer (PAL) and hole transport layer (HTL) is one of the determinants of photovoltaic performance and stability of PSCs. Herein, we introduce a bifunctional modifier of 4-hydroxy-2,2,6,6-tetramethylpiperidine (HTMP) at the interface of PAL/HTL. The hydroxyl and imino groups in HTMP can interact with I and FA (MA) to form bi-directional hydrogen bonds to inhibit ion migration, reinforce the interface contact, and improve perovskite stability. On the other hand, the bifunctional groups of HTMP can passivate interface defects by coordinating with Pb2+, provide a more suitable energy gradient arrangement, and reduce nonradiative recombination loss. Compared to the efficiency of 19.05% obtained from the unmodified device, the HTMP-modified PSC achieves a maximum power conversion efficiency of 22.04%, along with a negligible hysteresis effect and good environmental stability, indicating that HTMP plays an excellent role in efficient and stable PSCs.