Insights into the effects of oriented crystallization on the performance of quasi-two-dimensional perovskite solar cells

Long-term operational stability is one of the key problems for the commercialization of the perovskite photovoltaics. During the past decade, a tremendous amount of work has aimed at addressing the stability issues of perovskite solar cells (PSCs). Among them, the intrinsic instability of the ionic crystal structure of perovskite materials is foremost where proper strategies are highly required to complete the crystallization. Reducing the dimensional structure of the photoactive three-dimensional (3D) perovskites by the introduction of a non-photoactive two-dimensional (2D) perovskite phase is a rising topic recently, which generates a quasi-2D perovskite for improving the corresponding device stability. However, the power conversion efficiency (PCE) of quasi-2D perovskite solar cells decreases unfortunately with the increase of the 2D contents, which obviously depends on the orientation of the crystals. In this review, we first review the effect of the crystal orientation on the performance of quasi-2D PSCs. Then, the growth mechanism of the preferred crystal orientation is discussed in detail. The research progress of the modulation strategies which are key segments for the preferred oriented growth of quasi-2D perovskite crystals is summarized emphatically. Finally, we identify some challenges and opportunities for chasing efficient quasi-2D PSCs in furthering our understanding of the above themes.