Balance The Thickness, Transparency And Stability Of Semi-Transparent Perovskite Solar Cells By Solvent Engineering And Using A Bifunctional Additive

For semi-transparent perovskite solar cells (ST-PSCs), a common way to increase the average visible transmittance (AVT) of the perovskite relies on decreasing its thickness. However, such thin film always suffers imperfect film quality, particularly in a high-speed roll-to-roll processing, causing poor device stability. In this communication, we introduce a facile approach to improving the film transparency (AVT of ca. 30.7%) without obviously sacrificing its thickness (206 +/- 3 nm) via using a greener solvent system to confine the growth of the perovskite crystal size. The strategy would be compatible with large-area roll-to-roll processing. Actually, the perovskite with small crystal size suffers more bulk defects, resulting in decreased device efficiency and stability in ambient atmosphere. To overcome this issue, we also develop a bifunctional additive 1-propyl-[4,4'-bipyridin]-1-ium iodide (BiPy-I) to passivate antisite defects and positively charged defects in the perovskite, and simultaneously further improve the film transparency (AVT of ca. 32.2% @ 208 +/- 2 nm). As a result, the asprepared inverted ST-PSC produces an increased power conversion efficiency of 11.74% at a 23% AVT, and maintains ca. 91% of the original efficiency after a 240 h storage in ambient atmosphere.