The influence of the flexoelectric effect on materials properties with the emphasis on photovoltaic and related applications: A review

The research community is in permanent search of novel materials and exploitation of already elaborated phenomena to reveal yet unknown materials characteristics. Flexoelectricity has been in the spotlight lately because of its unique capacity to modulate electrical, optoelectronic, photovoltaic, and related properties and other characteristics of materials and devices. Nonetheless, potential limits on further progress of materials performance owing to incomplete knowledge about this effect are still not investigated to a sufficient extent. This review is focused on the most recent achievements on flexoelectric materials and on strain engineering strategies for modulating a strain gradient and flexoelectric response, with an emphasis on photovoltaic and related applications. Photodetectors based on flexoelectric materials and structures are discussed, and a brief overview of alternative (nonphotovoltaic) and emerging applications and challenges is provided. It is suggested that the most important materials for photovoltaic and related applications range from low-dimensional and thinfilm ferroelectric semiconductors (which for example can be designed in an alternative way, according to the "barrier layer capacitor" principle) to conducting materials that are not restricted by the Shockley-Queisser limit. Such materials enable ultrafast charge carrier separation and enhanced photocurrents, photovoltages, and other photoelectric parameters of devices under strain gradients, compared with available analogs.