Ethylene glycol-containing ammonium salt for developing highly compatible interfaces in perovskite solar cells

For achieving efficient and stable perovskite solar cells (PSCs), the interface between the perovskite absorber and charge transport material should be modulated to provide proper energy alignment, fast charge delivery, and suppressed charge recombination. In this study, a multifunctional interface modifier for PSCs was developed by the quaternization of trimethylamine with 1-bromo-2-(2-methoxyethoxy)ethane. This ethylene glycol-containing ammonium salt (EG) effectively passivates interfacial traps and induces dipoles on the surface of the perovskite, facilitating charge transfer/extraction at the perovskite/hole transport material (HTM) interface. Accordingly, after the interface modification with EG, the PSCs showed a high efficiency of over 24% with a representative doped SpiroOMeTAD HTM. Moreover, the EG modification was revealed to be highly compatibility with dopant-free HTMs, resulting in an improved efficiency of up to 22.01% in its corresponding photovoltaics compared to those of the control and conventional alkyl-based salt treatments (19.44% and 17.94%, respectively).