Synergy of structural contact and energy-level improvement on CuSCN/Au interface with cobalt(II) thiocyanate for achieving efficient and stable CuSCN-based perovskite solar cells

Copper(I) thiocyanate (CuSCN) is a relatively inexpensive and stable p-type hole transport material suitable for fabricating perovskite solar cells (PSCs). However, devices using CuSCN often exhibit poor stability due to severe degradation at the CuSCN/metal-electrode interface, and the root cause remains unclear. In this study, we address this issue by constructing a modified hole transport layer (HTL) through the introduction of an ultra-thin interlayer of cobalt thiocyanate (Co(SCN) 2 ) between CuSCN and the Au electrode. This strategy not only reduces the surface roughness of the CuSCN film surface but also establishes favorable energy level alignment, thereby improving hole extraction efficiency. Additionally, it prevents the degradation of CuSCN caused by the self-disproportionation reaction of Cu + in CuSCN (Cu +  = Cu 0  + Cu 2+ ) through the alloying of Cu/Au. Consequently, the PSC fabricated with the CuSCN/Co(SCN) 2 -layer achieves an impressive power conversion efficiency (PCE) of 19.38%, making it one of the highest efficiencies among dopant-free inorganic HTL-based PSCs. Importantly, the device with Co(SCN) 2 demonstrates overall enhancements in operational stability under continuous light illumination, moisture attack and thermal stress. This work finds a dual-interface passivation for making efficient and stable CuSCN-based PSCs with different device structures, which has a certain contribution to the surface & interface engineering of CuSCN-based PSCs.