Heating with light: photonic curing for photovoltaic technologies

The goal of this project is to develop "photonic curing" (PC) as a quick and selective method to replace thermal annealing in solar cell preparation. The thermal annealing indicates a treatment that most solar cells need, during which the photovoltaic device (included the substrate) is placed in an oven or on a hot-plate at certain temperature (ranging from few tens to hundreds of C) for different times (from seconds to hours). Consequently, the annealing limits the choice of substrates and compounds that can be used in a solar cell, depending on their thermal. For example, a commonly used transport layer, TiO2, requires annealing at 450C for several minutes. Clearly, this material, cannot be used on plastic substrates, that would melt during the annealing. To overcome this limitation, this project uses photonic curing, in which a short but powerful pulse from high voltage lamps is used as heat source. Differently from traditional thermal processes, in the photonic curing the energy comes from a lamp placed on top the device, only heating the uppermost layer of the multilayer structure that characterise solar cells. By changing the light pulse characteristics (power, duration, repetitions and frequency) it is possible to modulate the transmitted energy profile, adapting it to the light-absorption properties and to thermal conditions required by the material to be treated. Additionally, it is possible to carefully control the heating penetration depth, avoiding damages to the materials and substrates underneath the uppermost layer. Therefore, this could permit the preparation of novel solar cells architectures, as well as the improvement of existing single- and multi-junction devices. For example, delicate substrates (such as plastic or fabric) could be used, and novel combinations of small- and wide-bandgaps semiconductors for tandem PV devices could be explored. As such, the main objectives of this project will be: i) development of photonic curing treatments for the crystallization of different thin-films absorbers (perovskites, Sb2Se3, Cu2ZnSnS4) and different transport materials (TiO2, SnO2, ZnO2, MoOx or NiOx). ii) Preparation and characterization of thin-film single-junction solar cells through photonic curing on flexible substrates. iii) Preparation of novel multi-junction solar cells (so far hindered by the required thermal treatments) on rigid and flexible substrates. Thanks to the creation of novel photovoltaic modules able to satisfy both high efficiency and a wide range of prerequisites beyond performances (e.g. light weight and bendability, patterned designs, colour, etc.), this project will have an enormous impact on the academic, industrial, and social sector, unlocking a new technology and permitting large deployment of solar cells in different contexts.