Giant Photocaloric Effects across a Vast Temperature Range in Ferroelectric Perovskites

Solid-state cooling presents an energy-efficient and environmentally friendly alternative to traditional refrigeration technologies that rely on thermodynamic cycles involving greenhouse gases. However, conventional caloric effects face several challenges that impede their practical application in refrigeration devices. First, operational temperature conditions must align closely with zero-field phase-transition points; otherwise, the required driving fields become excessively large. However, phase transitions occur infrequently near room temperature. Additionally, caloric effects typically exhibit strong temperature dependence and are sizable only within relatively narrow temperature ranges. In this Letter, we employ first-principles simulation methods to demonstrate that light-driven phase transitions in polar oxide perovskites have the potential to overcome such limitations. Specifically, for the prototypical ferroelectric KNbO3 we illustrate the existence of giant "photocaloric" effects induced by light absorption (OSPC 100 J K-1 kg-1 and OTPC 10 K) across a vast temperature range of several hundred Kelvin, encompassing room temperature. These findings are expected to be generalizable to other materials exhibiting similar polar behavior.