MeO-PhPACz is a fully aromatic carbazole-based self-assembled monolayer (SAM) serving as a hole-selective layer (HSL) in highly efficient inverted wide-band gap perovskite solar cells (PSCs). MeO-PhPACz features a methoxy substituted carbazolyl terminal, a rigid phenyl linker, and a phosphonic acid anchor. The rigid phenyl linker not only extends the conjugation of the carbazole terminal, but also promotes the formation of a dense and highly ordered HSL on substrates.
With extended conjugation and ordered packing, MeO-PhPACz facilitates perovskite interfacial interactions and the growth of uniform perovskite films. The high-quality SAM film formed at the interface effectively improves the hole extraction/transport efficiency by suppressing interfacial non-radiative recombination. MeO-PhPACz also demonstrates heightened UV absorption capabilities and inherent UV resistance, substantially enhancing PSC thermal stability and resistance to UV light illumination.
A mixed SAM of MeO-PhPACz and Me-4PACz enhances the binding energies with indium tin oxide (ITO) for improved hole transport efficiency. Inverted wide bandgap PSCs based on the mixed self-assembled monolayer exhibit superior photostability and thermal stability, maintaining 90% of their initial efficiency after 900 h of damp-heat testing and showing minimal decay after 1,000 h under 1 sun light soaking. A monolithic perovskite/silicon solar cell based on the mixed-self-assembled-monolayer of Me-4PACz and MeO-PhPACz demonstrates a remarkable efficiency of 28.07% with great reproducibility.
Serving as hole selective contact for organic solar cells and perovskite solar cells, MeO-PhPACz is an alternative to PEDOT:PSS with superior performance and the convenience of solution deposition at low concentration, i.e. 1 mM.