Mitigating Iodine Diffusion by a MoO₃-Organic Composite Hole Transport Layer for Stable Perovskite Solar Cells

Halide perovskite solar cells (PSCs) exhibit commercialization potential, but long-term stability still has to be addressed. Among various products of perovskite decomposition, iodine species are of considerable concern due to their high vapor pressure and corrosive nature. To address this, a small-molecule hole transport layer (HTL), 4,4',4''-tris[(3-methylphenyl)phenylamino]triphenylamine (m-MTDATA), is used, and <i>p</i>-doped using molybdenum trioxide (MoO₃) to prevent an alternative oxidation reaction with iodine species that are released from iodide perovskites upon degradation. The resulting m-MTDATA:MoO₃ composite HTL demonstrates high conductivity and suppressed iodine permeation. We demonstrate that m-MTDATA:MoO₃ HTLs employed in PSCs improve stability under both thermal and voltage bias stress compared to devices with a conventional doped 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD) HTL.