Improving the Extraction of Photogenerated Electrons with SnO 2 Nanocolloids for Efficient Planar Perovskite Solar Cells

Great attention to cost‐effective high‐efficiency solar power conversion of trihalide perovskite solar cells (PSCs) has been hovering at high levels in the recent 5 years. Among PSC devices, admittedly, TiO 2 is the most widely used electron transport layer (ETL); however, its low mobility which is even less than that of CH 3 NH 3 PbI 3 makes it not an ideal material. In principle, SnO 2 with higher electron mobility can be regarded as a positive alternative. Herein, a SnO 2 nanocolloid sol with ≈3 nm in size synthesized at 60 °C was spin‐coated onto the fuorine‐doped tin oxide (FTO) glass as the ETL of planar CH 3 NH 3 PbI 3 perovskite solar cells. TiCl 4 treatment of SnO 2 ‐coated FTO is found to improve crystallization and increase the surface coverage of perovskites, which plays a pivotal role in improving the power conversion efficiency (PCE). In this report, a champion efficiency of 14.69% ( J sc = 21.19 mA cm −2 , V oc = 1023 mV, and FF = 0.678) is obtained with a metal mask at one sun illumination (AM 1.5G, 100 mW cm −2 ). Compared to the typical TiO 2 , the SnO 2 ETL efficiently facilitates the separation and transportation of photogenerated electrons/holes from the perovskite absorber, which results in a significant enhancement of photocurrent and PCE.