Modulation of elastic perovskites for flexible photovoltaics

The soft crystal structure of perovskite semiconductors enabled the construction of flexible perovskite solar cells (f-PSCs), which manifested promising power conversion efficiency (PCE) but fall short of mechanical durability. Herein, the recent progress and versatile application scenario of f-PSCs were summarized to disclose the practical requirements and fracture mechanics of perovskite thin films under applied external load. As it was unveiled that the mechanical failure of f-PSCs was generally initiated from the fragile perovskites because of their relatively low cohesive energy and fracture toughness, which can be modulated by finely adjusting their crystal quality or facilitating energy dissipation away from the perovskites. Accordingly, the intrinsic correlation between the chemical composition, lattice strain, grain size and layer thickness, grain boundaries and crystal orientation of the perovskite with its mechanical properties was established to guide the optimization of crystal quality with improved elasticity. Moreover, the external load on the perovskite can be effectively relaxed by incorporating self-healing materials, which are temporarily ascribed and then recovered under certain stimulus to impede crack formation and propagation. In the end, recent strategies to prolong the mechanical lifespan of the perovskite materials were systematically reviewed from which perspectives for further development of mechanically durable f-PSCs are provided.