Achieving High‐Quality Perovskite Films with Guanidine‐Based Additives for Efficient and Stable Methylammonium‐Free Perovskite Solar Cells

Abstract Power conversion efficiencies (PCEs) of the methylammonium‐free (MA‐free) perovskite solar cells (PSCs) are constantly lagging behind those of the most extensively researched triple cation mixed PSCs due to their subpar perovskite films. Here, two guanidine‐based passivation agents are proposed, that are, sulfaguanidine (S‐Gua) and 1‐acetylguanidine (A‐Gua) that can be applied to optimize the film quality of MA‐free perovskite for minimizing the efficiency discrepancy between the two types of PSCs. Through strong coordination with Pb²⁺ and hydrogen bonding with formamidinium (FA⁺), the two passivation additives can reduce bulk defects and suppress non‐radiative recombination, which in turn enhance the charge extraction and transfer efficiency. Consequently, the S‐Gua‐ and A‐Gua‐treated devices achieve PCEs of 24.34% and 23.77%, respectively. Both PCEs are greater than that of the control device (23.03%), and the 24.34% PCE is comparable with that of the best MA‐free inverted PSCs with narrower bandgaps. Moreover, the S‐Gua‐treated devices maintain 89.3% and 82.0% of their initial PCEs after aging for 800 h and heating (85 °C) for 340 h in ambient air without any encapsulation, respectively. This work offers comprehensive insights into the use of guanidine‐based additives to achieve high‐quality perovskite films and subsequently state‐of‐the‐art MA‐free PSCs.