There are various methods of making PDRCs 'switchable' to mitigate overcooling. Most research has used vanadium dioxide (VO2), an inorganic compound, to achieve temperature-based 'switchable' cooling and heating effects. While, as per Khan et al., developing VO2 is difficult, their review found that "recent research has focused on simplifying and improving the expansion of techniques for different types of applications." Chen et al. found that "much effort has been devoted to VO2 coatings in the switching of the mid-infrared spectrum, and only a few studies have reported the switchable ability of temperature-dependent coatings in the solar spectrum." Temperature-dependent switching requires no extra energy input to achieve both cooling and heating.