Perovskite solar cells (PSCs) have reached a power conversion efficiency (PCE) of over 25%. However, solution-processable perovskite films suffer from ionic defects at the surface and grain boundaries, which are harmful to the efficiency and stability of PSCs. Here, we employ a thiophene-based diammonium salt to passivate defects in PSCs and to investigate the passivation mechanism of undercoordinated Pb<sup>2+</sup> at both the surface and grain boundaries. We use solid-state NMR and X-ray photoelectron spectroscopy (XPS) to show that the sulfur of the thiophene molecule effectively reduces the defects on the perovskite surface through the Pb-S interaction. Our studies reveal that the addition of the thiophene-based salt results in passivation at both the surface and grain boundaries, leading to an increase in the open circuit voltage, stability, photoluminescence lifetimes, and reduction of non-radiative recombination compared to the control device.

Understanding the passivation mechanism of thiophene-based ammonium salts for stable and efficient perovskite solar cells

ACS Fall 2021

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