The aim of the GASPER project is to develop and fully characterize a new concept of gas diffusion photoelectrodes with backside illumination for CO2 conversion under solar light. To this end, we will take advantage of a very recent discovery by one of our partners that has made backside illumination of a CIGS solar cell possible (patent pending). We will then implement this device by adding a porous layer to the front of the photoelectrode into which we will insert a molecular catalyst. Several investigation tools will be employed, including fast time-resolved spectroscopy, to understand the elementary phenomena at play in the photoelectrode. At the same time, the data collected will be used to feed a multi-physics model simulating the transfer and transport steps and the associated kinetics, in order to optimize the photoelectrode structure by inverse design. Finally, the catalytic properties of the photoelectrode thus developed will be studied in detail for CO2 conversion.