Defect passivation is an effective method to improve the photoelectric conversion efficiency and stability of perovskite solar cells. Lewis base is one of the passivation additives commonly used in perovskite solar cells. It is defined as small organic molecules with electron-withdrawing functional groups such as C=O, S=O, P=O, and -CN. body. Molecules with proton functional groups (-OH, -NH, etc.) added to traditional Lewis bases show a more efficient passivation effect than pure Lewis bases, but the detailed mechanism of action has not been studied and proven. Theoretical calculations have proved that surface active oxygen (superoxide ion O2-) damages the stability of perovskite films and devices, but there are almost no relevant experimental studies on the passivation molecules that prevent the process of superoxide degradation of perovskite.
Functional nanostructure design and assembly of Fujian Institute of Structure of Matter, Chinese Academy of Sciences/Gao Peng, researcher at the Key Laboratory of Nanomaterials of Fujian Province, combined Lewis base functional groups and proton functional groups on polyaromatic conjugated molecules to obtain pure Lewis base system molecules 9CN-PMI and Lewis base/proton system molecule 4OH-NMI is introduced into the perovskite precursor solution to prepare passivated perovskite films and devices. The comparison of the characterization of two different types of molecules shows that the 4OH-NMI molecule with Lewis base/polyaromatic conjugate/proton structure can play a more excellent chemical passivation function, and its C=O/ The -OH functional group system can effectively passivate positive and negative charge defects and lead clusters. The -OH of the passivator can interact with I- through hydrogen bonds, thereby promoting the combination of C=O groups and anti-Pb2+ defects, so that The passivation effect is maximized. Theoretical calculations and stability tests have proved that 4OH-NMI has a more significant energy band passivation (Energetic passivation), that is, passivating molecules produce a benign intermediate energy gap state, which is located above the electron trap state generated by O2 , It can capture the photoexcited electrons on the perovskite before O2, avoid the formation of superoxide ions, and improve the stability of the perovskite device. In addition, the study also found that the addition of 4OH-NMI and 9CN-PMI can increase the viscosity of the perovskite precursor solution, thereby significantly increasing the thickness of the perovskite film to achieve higher light collection efficiency. After 4OH-NMI passivation, the efficiency of the perovskite cell reached 23.7% and showed excellent stability.
Related research results were published on Advanced Materials.
Defect state density, non-radiative recombination, related characterization of surface morphology; stability test and super oxygen theoretical calculation
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