Enabling the sunlight driven response of thermally induced shape memory polymers by rewritable CH3NH3PbI3 perovskite coating

Shape memory polymers (SMPs) have beenwidely used in our daily life (e.g. shrinkable tubes) and are expected to play more important roles in soft robotics, biomedical devices and other high-tech areas. Due to the energy shortage the world is facing now, it would be ideal to convert normal heat-driven SMPs into sunlight-responsive SMPs, so that solar energy could be converted into mechanical work. It is even more desirable to make SMPs flexibly switch between photoresponsiveness and photo-inertness. However, these objectives have not been realised so far. Here, we come up with a straightforward and low-cost method to do so by coating thermal-responsive SMPs with CH3NH3PbI3 perovskite. We find that CH3NH3PbI3 has excellent photo-thermal effect. As it can effectively convert solar energy into heat, the shape change of SMPs can be controlled by sunlight. The CH3NH3PbI3 layer can be easily washed off with water. The coating-erasing can be repeated many times to make the SMPs photoresponsive and photo-inert alternatively. The concept introduced here will not only expand the application of many currently available thermal-responsive SMPs, but also provide a practical method to make good use of solar energy.