Even though the mesoporous-type perovskite solar cell (PSC) is known for high efficiency, its planar-type counterpart exhibits lower efficiency and hysteretic response. Herein, we report success in suppressing hysteresis and record efficiency for planar-type devices using EDTA-complexed tin oxide (SnO₂) electron-transport layer. The Fermi level of EDTA-complexed SnO₂ is better matched with the conduction band of perovskite, leading to high open-circuit voltage. Its electron mobility is about three times larger than that of the SnO₂. The record power conversion efficiency of planar-type PSCs with EDTA-complexed SnO₂ increases to 21.60% (certified at 21.52% by Newport) with negligible hysteresis. Meanwhile, the low-temperature processed EDTA-complexed SnO₂ enables 18.28% efficiency for a flexible device. Moreover, the unsealed PSCs with EDTA-complexed SnO₂ degrade only by 8% exposed in an ambient atmosphere after 2880 h, and only by 14% after 120 h under irradiation at 100 mW cm⁻².

The efficiency of planar CH₃NH₃PbI₃ perovskite solar cells has been improved up to 19.62% using an ionic liquid to modify the TiO₂ electron transport layer, and the J–V hysteresis is completely eliminated.

Cs⁺doping into 2D (BA)₂(MA)₃Pb₄I₁₃perovskites boosts power conversion efficiency (PCE) to 13.7% and yields superior humidity and thermal stability.