With the rise of wearable electronics, the need for sustainable, portable power is increasing. To overcome battery limitations, energy harvesters converting solar, thermal, and mechanical energy into electricity have been developed. Mechanical energy, abundant but underused, can be captured via piezoelectric and triboelectric nanogenerators (PENGs and TENGs). TENGs offer high output and low-cost fabrication, with performance influenced by material properties and surface treatments. Halide perovskites (HPs) show strong potential for energy harvesting and storage due to their dielectric and piezoelectric properties. A recent MA₂SnCl₆-based self-charging unit combines a PENG with a lithium-ion battery. Lead-free, efficient HPs are vital for self-powered wearable devices.

Herein, we present the utilization of air-stable, 2D-layered, lead-free MA₃Bi₂I₉ for stretchable MA₃Bi₂I₉-SEBS (Styrene Ethylene Butylene Styrene) composite-based hybrid nanogenerators and as an electrode material in LIBs. Initially, high-performance, stretchable hybrid nanogenerators based on MA₃Bi₂I₉ (MBI; MA = CH₃NH₃) perovskite were developed by compositing with SEBS polymer to harvest mechanical energy in both PENG and TENG modes, achieving the highest output at 12 wt% film loading. Specifically, the 12 wt% TENG demonstrated an output voltage of 537 V and a power density of 3.04 mW/cm². Furthermore, the electrochemical performance of MA₃Bi₂I₉ as a cathode material was investigated, revealing high specific capacity and long-term cycling stability. Finally, we demonstrate the practical application of the developed hybrid nanogenerator by using it to charge the MA₃Bi₂I₉-based LIB. The charged LIB, powered by the TENG, is capable of operating small-scale electronic devices, including a smartwatch and a calculator.