10.1021/acsami.7b05146.s001 Yoon Ho Choi Yoon Ho Choi Hyun Bin Kim Hyun Bin Kim In Seok Yang In Seok Yang Sang Do Sung Sang Do Sung Young Sik Choi Young Sik Choi Jeongho Kim Jeongho Kim Wan In Lee Wan In Lee Silicotungstate, a Potential Electron Transporting Layer for Low-Temperature Perovskite Solar Cells American Chemical Society 2017 Li 4 SiW 12 O 40 CH 3 NH 3 PbI 3 PSC device electron OC TiO 2 layer FF PCE uniform Li-ST films photovoltaic conversion efficiency FTO ETL Li-ST layer Low-Temperature Perovskite Solar Cells 60 nm-thick Li-ST layer coating CH 3 NH 3 PbI 3 Li-ST buffer layer 2017-07-12 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Silicotungstate_a_Potential_Electron_Transporting_Layer_for_Low-Temperature_Perovskite_Solar_Cells/5226340 Thin films of a heteropolytungstate, lithium silicotungstate (Li<sub>4</sub>SiW<sub>12</sub>O<sub>40</sub>, termed Li-ST), prepared by a solution process at low temperature, were successfully applied as electron transporting layer (ETL) of planar-type perovskite solar cells (PSCs). Dense and uniform Li-ST films were prepared on FTO glass by depositing a thin Li-ST buffer layer, followed by coating of a main Li-ST layer. The film thickness was controlled by varying the number of coating cycles, consisting of spin-coating and thermal treatment at 150 °C. In particular, by employing 60 nm-thick Li-ST layer obtained by two cycles of coating, the fabricated CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> PSC device demonstrates the photovoltaic conversion efficiency (PCE) of 14.26% with <i>J</i><sub>SC</sub> of 22.16 mA cm<sup>–2</sup>, <i>V</i><sub>OC</sub> of 0.993 mV and FF of 64.81%. The obtained PCE is significantly higher than that of the PSC employing a TiO<sub>2</sub> layer processed at the same temperature (PCE = 12.27%). Spectroscopic analyses by time-resolved photoluminescence and pulsed light-induced transient measurement of photocurrent indicate that the Li-ST layer collects electrons from CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> more efficiently and also exhibits longer electron lifetime than the TiO<sub>2</sub> layer thermally treated at 150 °C. Thus, Li-ST is considered to be a promising ETL material that can be applied for the fabrication of flexible PSC devices.