Chalcogenide Molecule-Based Interface Passivation for Enhancing the Stability of Perovskite Solar Cells

Over the last decade, perovskite solar cell (PSC) has emerged as very promising future-generation solar cell technology with a power conversion efficiency (PCE) of over 25%. However, the long-term stability of PSC still remains a barrier to its commercialization. For improving the stability of the PSC different classes of defect passivators have been investigated [1-3]. Among them, Lewis base-based passivators have been shown to be particularly effective owing to their ability to passivate various Pb²⁺ and Pb⁰related defects. Nonetheless, there is a lack of clear understanding regarding the defect passivation mechanism of these Lewis bases, resultantly, the predictability of the passivation strength of different Lewis base molecules is poor. This creates a challenge in selecting the superior passivator molecules among the plethora of options that are available.<br/>In this talk, I will speak about our group’s effort to understand the comparative interface passivation strength among different chalcogenide-based defect passivators. In our recent work, we use three different organic passivators (of similar structure) decorated with different chalcogenide atoms, (O, S, and Se) to study their effect on the stability of the devices. We observe that the sulfide and selenide passivated devices show superior stability compared to both un-passivated and oxide-passivated ones. This excellent stability with the sulfide and selenide passivators is most likely due to their strong interaction with the Pb cation, which can be explained using the hard-soft-acid-base principle. By taking the idea forward, we have used Al-doped CuS (Al-CuS) as sulfur-based inorganic hole transport layers (HTL) in inverted architecture PSC [1]. Al-CuS HTL-based devices show superior stability compared to NiO HTL-based control devices. After 650 hours of storage (at 30% RH, 20 °C ), sulfide HTL-based devices retain more than 60% of their initial stability. In contrast, their oxide counterparts retain less than 40% of their original value in the same timeframe.<br/><br/>References:<br/>[1] A. Sadhu, L.H. Wong* et al, Advanced Functional Materials, 2021 31 (38), 2103807.<br/>[2] M Rai, L.H. Wong* et al, Advanced Energy Materials, 2021, 2102276.<br/>[3] S Lie, LH Wong, L Etgar*, ACS Applied Materials & Interfaces, (2022) 14 (9), 11339-11349.