Thin indium tin oxide nanoparticle films as hole transport layer in inverted organic solar cells

Indium tin oxide nanoparticles (ITO-NPs) were used as hole transport layer (HTL) in doctor-bladed inverted bulk-heterojunction organic solar cells. After the non-aqueous synthesis of ITO nanoparticles, a customized stabilization strategy was established. As result, ethylenediamine, a stabilizer with a low boiling point was used for an easy removal of the remaining organic compounds in the ITO-NP layer by a short annealing step at 120 °C. Furthermore, different post-processing treatments (thermal annealing and plasma treatment) on the ITO-NP layer were investigated to improve the electrical parameters of the solar cell. Using poly(3-hexylthiophen) as photoactive polymer, power conversion efficiencies of 3% were achieved with the incorporation of ITO-NPs as HTL, being almost as good as the efficiencies of the reference system where poly(3,4-ethylenedioxythiophene) was used as HTL.