Interfacial defect passivation via imidazolium bromide for efficient, stable perovskite solar cells

Abstract

In this study, 1-methyl-3-benzyl-imidazolium halides (BzMIMX, X = I, Br, Cl) were introduced to passivate the FAPbI₃/spiro-OMeTAD interface for efficient and stable PSCs. BzMIMBr exhibits the best passivation effect, in which Br⁻ ions can well passivate the iodide vacancy from the perovskite surface. In the meantime, the weak coordination interaction between N atoms from imidazole and Pb²⁺ cations also passivate under-coordinated Pb²⁺ and reduce interfacial defects to some degree. Interestingly, a very small amount of the BzMIMBr could penetrate the bulk perovskite to further passivate the grain boundaries of the bulk perovskite film. The champion PCE of our small-size PSC devices can reach 25.3% with negligible hysteresis. Besides, π–π self-assembly from the BzMIM⁺ can strengthen the interfacial modification effect, which enhances the anti-humidity ability of perovskite films and the devices. When stored under ambient conditions (20 °C and 20% RH) for over 5000 h, this modification helps the cell to maintain 90% of its initial efficiency, indicating its good long-term stability. BzMIMBr-modified devices exhibit much better operational stability by maintaining 91% of the initial efficiency after 1000 h of continuous illumination with a bias voltage near the maximum power point. Our osmotic modification strategy provides a feasible way to achieve high-performance and stable PSCs.