Hot carriers : to be or not to be

Hot carriers are naturally produced in semiconductors after solar light absorption and observation abound of hot carriers in photovoltaic absorbers, especially nanostructured: MQW, NW or QD, but they have also been reported recently in halide perovskites and in photoelectrochemical systems. Long lived, they are an opportunity to mitigate thermalization losses during the photovoltaic conversion and therefore increase the efficiency of conversion. Hot carriers, that are more energetic than fully thermalized ones, are also known in other devices for their ability to induce defects. Are they an opportunity or a liability? We will present, from our latest results, what we understand in terms of thermalization of hot carriers in solar cell devices, how these could potentially be harnessed to improve the efficiency of new generation of photovoltaic converters : how fast they relax, how far they travel, and what are the strategies to best take advantage of slow thermalization rates in hot carrier devices, whether in devices designed to operate as hot carrier solar cells or devices in which hot carrier effect could play a part. Finally, we will discuss how hot carriers can be clearly identified, when experiments are ambiguous or when they likely point at a different phenomenon, potentially related to material degradation.