The need for clean and renewable energy, as well as constantly improved numerical performances have been two of the most important driving forces in research worldwide. In this light, multiferroic materials, which are materials presenting several ferroic order, have been widely investigated towards their application in electronics and computation, or as sensors. Recently, they have been also considered for their potential use to generate energy through the photovoltaic effect. However, power conversion have remained poor compared to existing technologies such as p-n junction silicon based solar cells, mainly because of their wide bandgap and low mobility of the carriers. Nevertheless, multiferroic materials often present a vast number of degrees of freedom, and their interaction with light cannot be reduced to the sole photovoltaic effect.In this work, we study from first-principles the interaction of light and strain in the multiferroic bismuth ferrite, and find that the so-called photostriction effect originates from a screening of the polarization at the unit cell scale, which results in a photo-induced strain via the action of the converse piezoelectric effect. A solid solution of lead nickel niobium and lead titanate, exhibiting large electromechanical properties at its morphotropic phase boundary, is then synthesized, and its optical and photoinduced properties are studied. Also, the influence of defects at domain walls in the model ferroelectric lead titanate is studied from ab-initio calculations, in order to understand why domain walls exhibit a large conductivity compared to the domains. It is found that defects are more likely to form at the domain wall, and provide it with extra-carriers. Eventually, the advances in a recently considered spin-orbit energy term, the Angular MagnetoElectric coupling (AME), are considered and applied to the Inverse Faraday Effect (IFE), that is the existence of a magnetic field induced by circularly polarized light.