Stable electron transport materials (ETMs) with fewer surface defects and proper energy level alignments with halideperovskite active layers are required for efficient perovskite solar cells (PSCs) with long-term durability. Here,two-dimensional van der Waals mixed valence tin oxides Sn2O3and Sn3O4 are controllably synthesized and applied asETMs for planar PSCs. The synthesized Sn2O3 and Sn3O4have size of 5−20 nm and disperse well in water as stablecolloids for months. Both Sn2O3 and Sn3O4exhibit typical n-type semiconductor energy band structures, low trap density,and suitable energy level alignments with halide perovskites. Steady-statepower conversion efficiencies (PCEs) of22.36% and 21.83% are obtained for Sn2O3-based and Sn3O4-basedplanar PSCs. In addition, the half cells without hole transport materials andback electrodes show good UV-stability with average PCE of 99.0% and 95.7% forSn2O3-based and Sn3O4-based devicesremaining after 1000 h of ultraviolet soaking with an intensity of 70 mW cm−2.
(a) Photos of SnO2, Sn2O3,and Sn3O4 dispersions and SnO precipitation in water. (b)Photos of powders obtained by freeze-drying. (c−f)Theoretical crystal structure of (c) SnO2, (d) Sn2O3,(e) Sn3O4 and (f) SnO. (g) Band alignments with halideperovskites. (h) J−V curves of PSCs based on three tin oxides at reverse sweep.
