Stretchable Perovskite Solar Cells with Recoverable Performance.

Perovskite solar cells (PSCs) are a promising photovoltaic technology for stretchable applications because of their flexible, light-weight, and low-cost characteristics. However, the fragility of crystals and poor crystallinity of perovskite on stretchable substrates results in performance loss. In fact, grain boundary defects are the "Achilles' heel" of optoelectronic and mechanical stability. We incorporate a self-healing polyurethane (s-PU) with dynamic oxime-carbamate bonds as a scaffold into the perovskite films, which simultaneously enhances crystallinity and passivates the grain boundary of the perovskite films. The stretchable PSCs with s-PU deliver a stabilized efficiency of 19.15 % with negligible hysteresis, which is comparable to the performance on rigid substrates. The PSCs can maintain over 90 % of their initial efficiency after 3000 hours in air because of their self-encapsulating structure. Importantly, the self-healing function of the s-PU scaffold was verified in situ. The s-PU can release mechanical stress and repair cracks at the grain boundary on multiple levels. The devices recover 88 % of their original efficiency after 1000 cycles at 20 % stretch. We believe that this ingenious growth strategy for crystalline semiconductors will facilitate development of flexible and stretchable electronics.