Efficient and stable perovskite solar cells via shortwave infrared polymer passivation

Defect passivation plays an important role in the performance of perovskite solar cells (PSCs). Here, a narrow bandgap conjugated polymer with hole mobility of 3.4 x 10(-4) cm(2) V-1 s(-1) is utilized as a passivation agent in the fabrication of air-prepared PSCs. Theoretical calculations complemented by Fourier transform infrared absorption spectroscopy (FTIR) demonstrate that N, S and O atoms in the polymer can behave as Lewis bases, which interact with Pb defects in the MAPbI(3) films to passivate grain boundaries (GBs) and interface defects. These interactions synergistically promote an enhancement of the crystallinity and smoothness of the films. Solar cells fabricated with the polymer passivation layer exhibit average efficiencies of 18.7%-19.6% compared to an average of 16.7% for reference devices. Unencapsulated devices retained approximately 80% of their initial efficiency following 600 h of exposure in air, compared with similar to 30% for reference devices. The moisture stability of the devices was also dramatically improved owing to the long hydrophobic alkyl chains within the polymer. This study demonstrates that narrow bandgap materials with tailored functionality can dramatically improve the PCE and stability of PSCs and shed light on the design of the passivants that further improve film quality and device performance.