A Holistic Approach of Enhancing Efficiency and Stability of Perovskite Solar Cells and Their Tandem Solar Cells with Organics

Minimizing energy loss through defect passivation and increasing the quality of crystalline perovskite films are keys to improve the performance and long-term stability of perovskite solar cells. To address these challenges, we have developed several multifunctional, nonvolatile additives that can be used to modulate the kinetics of perovskite film growth to enable large-sized grains and coherent growth of perovskites from bottom to surface to be achieved. In addition, we have developed a holistic strategy to improve each interface of the inverted device structure. The improved film morphology and interfaces resulted in significantly reduced non-radiative recombination, helping enhance the power conversion efficiency (PCE) of inverted (p-i-n) device to >26.5% with low energy loss and good long-term stability at 85°C under operation conditions. In addition, these multifunctional additives can also be applied to address one of the most challenging problems involved in large bandgap perovskites and their derived devices for single junction and tandem solar cells. The commonly observed halide segregation critically limits the stability of mixed-halide perovskites under device operational conditions. There is a strong indication that halide movement/oxidation is the primary driving force behind halide de-mixing. To alleviate this problem, we have developed a series of multifunctional mediators that can suppress these factors while simultaneously passivate defects through tailored substitution. These effects enable wide-bandgap (1.79-1.81 eV) perovskite solar cells to achieve an outstanding PCE >20%, with 95% of its initial PCE retained after tracking at maximum power point for 500 h. Integrating this layer into a monolithic perovskite-organic tandem solar cell as a wide-bandgap subcell afforded a record-high PCE of 26.2% and impressive long-term operational stability.