Precursor‐Engineered Volatile Inks Enable Reliable Blade‐Coating of Cesium–Formamidinium Perovskites Toward Fully Printed Solar Modules

Abstract

Abstract Reliable fabrication of large‐area perovskite films with antisolvent‐free printing techniques requires high‐volatility solvents, such as 2‐methoxyethanol (2ME), to formulate precursor inks. However, the fabrication of high‐quality cesium–formamidinium (Cs–FA) perovskites has been hampered using volatile solvents due to their poor coordination with the perovskite precursors. Here, this issue is resolved by re‐formulating a 2ME‐based Cs0.05FA0.95PbI3 ink using pre‐synthesized single crystals as the precursor instead of the conventional mixture of raw powders. The key to obtaining high‐quality Cs–FA films lies in the removal of colloidal particles from the ink and hence the suppression of colloid‐induced heterogeneous nucleation, which kinetically facilitates the growth of as‐formed crystals toward larger grains and improved film crystallinity. Employing the precursor‐engineered volatile ink in the vacuum‐free, fully printing processing of solar cells (with carbon electrode), a power conversion efficiency (PCE) of 19.3%, a T80 (80% of initial PCE) of 1000 h in ISOS‐L‐2I (85 °C/1 Sun) aging test and a substantially reduced bill of materials are obtained. The reliable coating methodology ultimately enables the fabrication of carbon‐electrode mini solar modules with a stabilized PCE of 16.2% (average 15.6%) representing the record value among the fully printed counterparts and a key milestone toward meeting the objectives for a scalable photovoltaic technology.

Keywords

• cesium formamidinium perovskite
• reliable blade coating
• single crystals
• solar module
• volatile ink