Copper naphthalocyanine-based hole-transport material for high-performance and thermally stable perovskite solar cells

Metal phthalocyanines (MPcs) have gained considerable research attention as hole-transport materials (HTMs) in perovskite solar cells (PSCs) because of their superb stability. However, the photovoltaic performance of MPc-based HTMs in PSCs is still lagging behind their small molecule and polymeric counterparts, largely due to their relatively low hole mobility. Here, we report for the first time the application of a copper naphthalocyanine derivative (namely tBu-CuNc) as a hole-transport material (HTM) in perovskite solar cells (PSCs), and systematically study its optoelectronic and photovoltaic property compared with its CuPc analog (tBu-CuPc). Combined experiments disclose that the extension of π-conjugation from Pc to Nc core leads to not only an enhanced hole-carrier mobility associated with a stronger intermolecular interaction, but also an elevated glass transition temperature (T_g) of 252 °C. The resultant PSCs employing tBu-CuNc deliver an excellent power conversion efficiency of 24.03%, which is the record efficiency reported for metal complex-based HTMs in PSCs. More importantly, the encapsulated tBu-CuNc-based devices also show dramatically improved thermal stability than the devices using the well-known Spiro-OMeTAD, with a T₈₀ lifetime for more than 1,000 h under damp-heat stress. This study unfolds a new avenue for developing efficient and stable HTMs in PSCs.