Synthesis and Application of a Star-Shaped, Conjugated Oligomer Containing a Spiro(Fluorene-9,9'-Xanthene) Core for Copper(I) Thiocyanate Based Perovskite Solar Cells

Copper(I) thiocyanate (CuSCN) is a cost-effective and excellent inorganic p-type semiconductor; it has attracted considerable attention as hole-transporting material for highly efficient perovskite solar cells (PSCs) in recent years. However, various interface issues are currently regarded as the main obstacles for the CuSCN-based PSCs. Herein, we designed and synthesized a star-shaped oligomer (SFX-10) based on a spiro(fluorene-9,9’-xanthene) core terminated with fluorene groups by a simple Sonogashira coupling reaction, and its molecular structure was characterized with 1H, 13C NMR spectra and a high-resolution mass spectrum. The thermal, optical, and electrochemical properties of SFX-10 were fully investigated. SFX-10 shows good thermal stability with a high glass transition temperature of 138 °C. The photovoltaic performance measurements demonstrated that the CuSCN-based PSC using SFX-10 as an interlayer shows an evident improvement in power conversion efficiency of 6.61% compared with 5.52% for the bare device due to the passivation effect of the perovskite surface and the enhancement of the interfacial contact between the perovskite and CuSCN layers.