Dual-Functional Passivation Agent of Natural Dye Congo Red For Enhanced Carbon-Based Perovskite Solar Cells.

Carbon-based perovskite solar cells (C-PSCs) have acquired broad interest due to their superior stability and lower cost compared with metal-based perovskite solar cells (M-PSCs). However, the presence of perovskite defects greatly limits the power conversion efficiency (PCE) and long-term stability of C-PSCs. Herein, a natural dye Congo red molecule containing dual-functional groups of amino and sulfonic acids is first used as a surface passivation agent to treat the surface of perovskite films. High-quality perovskite films with reducing surface defect density and inhibiting nonradiative recombination are obtained. It is shown that the Congo red molecules not only effectively interact with the perovskite, enhancing the crystallization and enlarging the crystal size, but also demonstrate positive contribution for light harvesting in the visible range. The maximum PCE of 16.22% is achieved at the optimal concentration of 0.2 mg/mL Congo red, which is much higher than 13.57% for the control device. After 840 h of storage at 30-40% relative humidity at room temperature, the unencapsulated C-PSCs can still maintain a high initial performance of 87.21% compared with 43.26% for the control cells.