A Binary Solution Strategy Enables High-Efficiency Quasi-2D Perovskite Solar Cells with Excellent Thermal Stability

Quasi-two-dimensional(2D) perovskites are highly promising light-harvestingmaterials for commercialization of perovskite solar cells (PSCs) owingto the excellent materials stability. However, the coexistence ofmultiple n-value species in 2D perovskites oftencauses increased complexities in crystallization that can negativelyaffect the eventual photovoltaic performance. Herein, we present abinary solution based strategy via introducing nontoxic and widelyaccessible CH3COOH (HAc) as a co-solvent for preparinghigh-quality 2D perovskite films. Based on a 2D perovskite model system,(AA)(2)MA(4)Pb(5)I(16) (n = 5), we show that the prenucleation and grain growthkinetics are appreciably modified with HAc, which benefits from thestrong electron-donating ability of HAc with the key component ofPbI(2), leading to formation of favorable cluster aggregatesand resultant modulation of crystal growth. With the HAc-based method,the devices yield a boosted photovoltaic efficiency of 18.55% withan impressive photovoltage of 1.26 V. The champion cells exhibit asupreme thermal stability, showing <3% efficiency degradation undercontinuous thermal aging for 800 h.