Effective Multifunctional Additive Engineering for Efficient and Stable Inverted Perovskite Solar Cells

Fabricating high‐quality perovskite films with large grain sizes and low‐defect densities is critical for developing efficient and stable perovskite solar cells (PeSCs). Herein, a simple and effective multifunctional additive engineering strategy is reported for producing high‐quality perovskite films. By including 2‐hexyl‐thiophene (2HT) with a thiophene electron‐pair donor and a long hydrophobic alkyl chain as an additive in the perovskite precursor solution, a perovskite film with high crystallinity, decreased trap density, and hindered ion migration is successfully obtained. These features are attributed to the strong coordinative interaction between the sulfur atom in 2HT and Pb2+ in the perovskite film. The long alkyl chain of the 2HT additive assisted the production of a superior perovskite film with enlarged grain size, smooth surface topography, and hydrophobicity. Consequently, improved efficiency and prolonged operational stability are realized simultaneously for an inverted MAPbI3PeSC with the 2HT additive. The device with 2HT delivers a higher power conversion efficiency of 20.61% compared with that of the control device (18.65%) and exhibits negligible hysteresis. Moreover, the stability of the device with the 2HT additive is superior to that of the control device under various testing conditions.