PEIE-mediated strategies for highly efficient and stable perovskite solar cells overcoming BCP thermal aggregation

Abstract

Perovskite solar cells (PSCs) have attracted considerable research interest in recent decades due to their remarkable power conversion efficiencies. However, their thermal stability remains one of the crucial challenges for commercial applications. Bathocuproine (BCP), widely employed as an interfacial buffer layer between the electron transport layer and the metal electrode, tends to undergo thermal aggregation at elevated temperatures, thereby compromising device stability. In this paper, the aggregation behavior of BCP under thermal stability testing was investigated. It was proposed that introducing polyethylenimine ethoxylated (PEIE) into BCP could inhibit its high-temperature aggregation. The –NH and –OH groups in PEIE can form hydrogen bonds with the pyridine nitrogen in BCP. This interaction enables moderate π–π stacking to persist over a broader temperature range, thereby improving morphology and uniformity of the film. Concurrently, PEIE optimizes energy level alignment at the C₆₀/BCP interface, facilitating more efficient electron extraction and transport. Moreover, the incorporation of PEIE remarkably suppresses the infiltration of Ag ions under continuous thermal conditions, which further enhances the thermal stability of the device. By utilizing the PEIE-modified BCP buffer layer, the resulting PSCs demonstrate a champion power conversion efficiency (PCE) of 25.81%. Even after 1000 hours of operation under a relative humidity of 30%, they still retain an efficiency of more than 85%, demonstrating significantly enhanced stability. This work presents an innovative design strategy for developing PSCs with simultaneously enhanced efficiency and operational stability.