Insights into the Mechanism of Solid-State Metal Organic Complexes as Controllable and Stable p-Type Dopants in Efficient Planar Perovskite Solar Cells

Perovskite solar cells (PSCs) based on spiro-OMeTAD have achieved efficiencies greater than 20% in recent years; however, poorly designed dopants and ambiguous working mechanisms are still obstacles that restrict the process of commercialization. Various dopants have been introduced to modulate the electrical properties of spiro-OMeTAD, often accompanying some negative problems, such as complex synthetic routes and accelerated degradation of perovskite. Here, two novel metal organic complexes (Cu-2Cl and Cu-4Cl) with similar molecular fragments are designed and synthesized to investigate the effects on the chemical p-doping of spiro-OMeTAD. The unique coordination environment of copper ions and harmless oxidation byproducts make Cu-2Cl superior for oxidation of spiro-OMeTAD, and the possible synergetic mechanism of the heterogeneous reactions with Li-TFSI is also proposed. Utilizing Cu-2Cl-doped hole transport materials to fabricate PSCs will facilitate hole transport, reduce interfacial charge recombination, and passivate the trap states of perovskite, resulting in a champion efficiency of 20.97%. In addition, the intrinsic solid-state hydrophobic characteristics of Cu-2Cl nanoparticles well dispersed in the hole transport layer successfully suppress the invasion of water vapor, and the corresponding device retains 84% of its original efficiency after being stored for 720 h in ambient air condition.