Soybean Lecithin as a Passivator and Compatibilizer in p-i-n Perovskite Solar Cells

The low affinity caused by the mismatched surface energies between the perovskite precursor solution and the underlayer is the main reason for the poor coverage of perovskite films, which is also accountable for the pinholes in the perovskite films. To solve this problem, amphiphilic soybean lecithin (denoted as SL), which has two long aliphatic chains, is incorporated into the PbI₂ precursor solution. The amphiphilic nature of SL improves the coverage of perovskite films on hydrophobic PTAA, which is conducive to the fabrication of large-scale devices. In addition, the C═O, P═O, and quaternary ammonium groups in the zwitterion segment can passivate charged defects, thus decreasing the defect density of perovskite films. Notably, the power conversion efficiency (PCE) of the corresponding perovskite solar cells (Pero-SCs) with an active area of 0.1 cm² increased from 20.12 to 22.93%. Furthermore, the SL-doped devices with a larger active area of 1.1 cm² achieved the champion PCE of 18.32%. Moreover, the SL-doped Pero-SCs showed better humidity stability than did the control Pero-SCs.