Perovskite solar cells (PSCs) have reached impressively high efficiencies in a short period of time; however, the optoelectronic properties of halide perovskites are surprisingly complex owing to the coupled ionic...

Hybrid metal halide perovskites are mixed ionic-electronic semiconductors with exceptional optoelectronic properties, ideal for applications in photovoltaics, [1][2][3] lighting, [4] lasing, [5] X-ray detection, [6] among others. In all these applications, robustness and stability of the material are crucial. Bearing in mind that perovskites are ionic materials, it is expected that ion migration plays a significant role in all stability issues under operational conditions that often are triggered by irreversible ionic displacements. [7] The mixed ionic-electronic nature of metal halide perovskites was first described by Eames and co-workers in 2015. [8] Mobile ion defects have been widely acknowledged to influence charge transport in perovskite solar cells (PSCs) through generation of an electrostatic field profile that partially screens the field due to the applied bias and built-in voltage. [9,10] One of the most studied manifestations of ion migration in PSC is current-voltage hysteresis.

Despite the youthfulness of hybrid halide perovskite solar cells, their efficiencies are currently comparable to commercial silicon and have surpassed quantum‐dots solar cells. Yet, the scalability of these devices is a challenge due to their low reproducibility and stability under environmental conditions. However, the techniques reported to date to tackle such issues recurrently involve the use of solvent methods that would further complicate their transfer to industry. Herein a reliable alternative relaying in the implementation of an ultrathin plasma polymer as a passivation interface between the electron transport layer and the hybrid perovskite layer is presented. Such a nanoengineered interface provides solar devices with increased long‐term stability under ambient conditions. Thus, without involving any additional encapsulation step, the cells retain more than 80% of their efficiency after being exposed to the ambient atmosphere for more than 1000 h. Moreover, this plasma polymer passivation strategy significantly improves the coverage of the mesoporous scaffold by the perovskite layer, providing the solar cells with enhanced performance, with a champion efficiency of 19.2%, a remarkable value for Li‐free standard mesoporous n‐i‐p architectures, as well as significantly improved reproducibility.

Schematic representation of the solar cell configuration with alkylphosphonium modified perovskite layer.