Ionic liquid modified SnO2 nanocrystals as a robust electron transporting layer for efficient planar perovskite solar cells

Control over charge carrier transport in a low-temperature processed device is of key significance to realize high-performance perovskite solar cells (PSCs) and tandem solar cells. For low-temperature processed perovskite devices, a great challenge still remains due to the commonly inferior crystallinity and poor electron mobility of low-temperature processed electron transport materials. Meanwhile, electron transport layers (ETLs) produced at low-temperature show poor capability of managing the quality of overlying perovskite films, leaving abundant defects at grain boundaries, which hinder the efficient charge carrier transport or even result in severe energy loss by trap-assisted recombination. Here we present highly efficient PSCs realized by employing a tetramethylammonium hydroxide (TMAH) modified SnO2 ETL prepared at low-temperature (100-150 degrees C). TMAH modified SnO2 significantly enhances not only the conductivity of the SnO2 ETL for efficient electron extraction but also the electronic properties of the overlying perovskite film for fast electron transport across the grain boundaries. With this proposed novel ETL, an average efficiency above 20% is achieved for the low-temperature-processed PSCs, with an even higher efficiency exceeding 21% for the champion device. These low-temperature processed PSC devices also show reliable reproducibility and stability.