Self-Assembled Multilayers Reduce Interfacial Energy Loss in Perovskite Solar Cells

Abstract The use of self-assembled multilayer (SAM) layers as hole transport layers (HTLs) represents a major advance for high-efficiency perovskite solar cells (PSCs). However, many SAMs materials suffer from aggregation, poor wettability, and weak interactions with the perovskite, which hinder charge transfer and cause energy losses that limit both power conversion efficiency (PCE) and long-term stability. In this study, we synthesized two SAMs, namely 2-(10-(3,5-dimethoxyphenyl)−7H-benzo[c]carbazol-7-yl)ethyl)phosphonic acid (denoted as DMPA) and 2-(7H-benzo[c]carbazol-7-yl)ethyl)phosphonic acid (denoted as BCPA). DMPA SAM effectively suppresses self‑aggregation and enhances substrate coverage. The methoxy groups in DMPA interact with the perovskite, thereby enabling DMPA to passivate defects at the buried interface and optimize perovskite crystallization. These interfacial improvements facilitate more efficient charge extraction and enhance interfacial stability. As a result, DMPA-based PSCs achieve a PCE of 27.59% (certified PCE of 27.2%) and show remarkable photothermal stability, retaining 94.5% of their initial efficiency after 1600 hours of continuous illumination under 1 Sun at 65 °C.