Improved Interface Charge Extraction by Double Electron Transport Layers for High-Efficient Planar Perovskite Solar Cells

Charge extraction by electron transport layers (ETLs) plays a vital role in improving the performance of perovskite solar cells (PSCs). Here, PSCs with four different types of ETLs, such as SnO2, amorphous-Zn2SnO4 (am-ZTO), am-ZTO/SnO2, and SnO2/am-ZTO, are successfully synthesized. The interface recombination behavior and the charge transport properties of the devices affected by four types of ETLs are systematically investigated. For dual am-ZTO/SnO2 ETLs, compact am-ZTO ETL prepared by the pulsed laser deposition method provides a dense physical contact with FTO than the spin coating films, decreasing leakage current and improving charge collection at the interface of ETL/FTO. Moreover, dual am-ZTO/SnO2 ETLs lead to large free energy difference (Delta G), improving electron injection from perovskite to ETLs. One additional electron pathway from perovskite to am-ZTO is formed, which can also improve electron injection efficiency. A power conversion efficiency of 20.04% and a stabilized efficiency of 19.17% are achieved for the device based on dual am-ZTO/SnO2 ETLs. Most importantly, the devices are fabricated at a low temperature of 150 degrees C, which offers a potential method for large-scale production of PSCs, and paves the way for the development of flexible PSCs. It is believed that this work provides a strategy to design ETLs via controlling Delta G and interface contact to improve the performance of PSCs.