Searching for stability at lower dimensions: current trends and future prospects of layered perovskite solar cells

Astounding development of organic-inorganic halide perovskite solar cells (PSCs) in the past decade has been led by three-dimensional (3D) perovskites. Nevertheless, the concern over the stability of 3D PSCs casts a shadow on their real-world applications. By adopting various technological and scientific approaches, some progress has been made in improving the stability of 3D perovskite devices. Nonetheless, the best, definitive solution consists in improving the inherent chemical stability of the halide perovskite itself. Two-dimensional (2D) perovskites, on the other hand, display excellent stability under ambient conditions and have been recognized as an alternative to their 3D analogs. Although the first generation 2D PSCs have shown relatively lower photovoltaic performance, recent reports suggest that they are also capable of achieving high power conversion efficiency well beyond 20%. In the wake of the recent resurgence of 2D halide perovskite materials, we review their structural and optoelectronic properties, followed by an extensive analysis of recent progress in 2D PSCs.