SpiroOMeTAD

Spiro-OMeTAD is a widely used organic hole-transport material in perovskite solar cells. It is a spirobifluorene-based small molecule, typically described by the chemical name 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamino)-9,9'-spirobi[fluorene]. The compound is known for forming smooth, amorphous thin films that can effectively transport positive charges.

In perovskite devices, Spiro-OMeTAD functions as the hole-transport layer, extracting holes from the perovskite absorber and delivering them to the electrode. In its pristine form, the material has limited conductivity; performance is achieved by incorporating dopants that oxidize Spiro-OMeTAD to a higher-conductivity state.

A common formulation uses lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI) and 4-tert-butylpyridine (tBP) as dopants. These additives increase the concentration of Spiro-OMeTAD radical cations, boosting hole mobility. The exact concentrations and solvent choice (often chlorobenzene or related solvents) influence device efficiency and stability.

Spiro-OMeTAD is compatible with typical perovskite layers and helps achieve high open-circuit voltages and good interfacial contact with the gold electrode. However, the material is relatively expensive, and its performance relies on dopants that can affect long-term stability in the presence of moisture and oxygen. As a result, research continues into dopant-free variants and alternative hole-transport materials, while Spiro-OMeTAD remains a standard benchmark in laboratory-scale PSC studies.