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 must 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; mixing it with molybdenum trioxide (MoO₃) p-dopes the layer and slows 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.