Thiamine additive engineering enables improved film formation towards high efficiency and moisture stability in perovskite solar cells

Perovskite solar cells (PSCs) attract widespread research interest due to their exceptional properties. However, the instability of the perovskite layer, especially the moisture instability, and existing defects seriously restrict the performance and limit the development of PSCs towards commercialization. Herein, we fabricate moisture-stable and efficient PSCs by incorporating a thiamine (THM) additive into a lead iodide (PbI2) precursor using a two-step spin-coating method. This strategy enables a better interaction between the THM additive and PbI2. Then, a higher energy barrier is produced when the material reacts with A-site cations to form perovskite crystals, resulting in larger grains and better-quality perovskite films. Through optimization of the concentration of the THM additive, the optimal perovskite achieves improved moisture stability and decreased trap states; thus, the corresponding unencapsulated devices achieve a remarkable power conversion efficiency (PCE) of 21.40% and maintain >92% of their initial PCE after 180 h in ambient air (∼50% humidity). The excellent performance is mainly attributed to the fact that THM promotes crystal growth and passivates defects in perovskite films.