Unveiling and Modulating the Interfacial Reaction at the Metal–Hole Conductor Heterojunction toward Reliable Perovskite Solar Cells

Abstract

Interfaces between functional layers in perovskite solar cells (PSCs) are of paramount importance in determining their efficiency and stability, but the interaction and stability of metal−hole conductor (HC) interfaces have received less attention. Here, we discover an intriguing transient behavior in devices which induces a profound efficiency fluctuation from 9 to 20% during the initial performance testing. Air exposure (e.g., oxygen and moisture) can significantly accelerate this nonequilibrium process and simultaneously enhance the device maximal efficiency. Structural analysis reveals that the chemical reaction between Ag and HC occurred during the metal deposition by thermal evaporation, leading to the formation of an insulating barrier layer at their interfaces, which results in a high chargetransport barrier and poor device performance. Accordingly, we propose a metal diffusion-associated barrier evolution mechanism to understand the metal/HC interfaces. To mitigate these detrimental effects, we strategically develop an interlayer strategy by introducing an ultrathin layer of molybdenum oxide (MoO 3 ) between Ag and HC, which is found to effectively suppress the interfacial reaction, yielding highly reliable PSCs with instant high efficiency. This work provides new insights into understanding the metal−organic interfaces, and the developed interlayer strategy can be generally applicable to engineer other interfaces in realizing efficient and stable contacts.

Conjugated Phosphonic Acids Enable Robust Hole Transport Layers for Efficient and Intrinsically Stable Perovskite Solar Cells

“…To confirm this, we fabricated the film based on the mixture of CPAs and LiTFSI to monitor the FTIR peak shift corresponding to the vibrational mode of LiTFSI. [ 35 ] As displayed in Figure 2C, the corresponding peak was shifted to smaller wavenumbers once the CPAs were blended into the films, confirming the chemical interactions between CPAs and LiTFSI. To reveal the reaction mechanism between phosphonic acids and Li + , X‐ray photoelectron spectroscopy (XPS) was further performed (Figure 2D,E).…”