Stabilisation of Perovskite photovoltaic devices by passivation with Metal-Organic Frameworks type materials

MOFs are a type of porous organic-inorganic hybrid material with interesting properties in terms of the passivation of defects in the perovskite and its stability, particularly versus light. For example:
- Direct effect of MOF components as passivation agents: Metal ions and organic ligands can passivate defects at the MOF/PK interface.
- Downconversion of incident radiation: Certain metals (such as europium) or ligands (with aromatic groups) can absorb high-energy radiation (typically violet/near-UV), then re-emit this energy in the form of lower-energy radiation or transmit it directly in a non-radiative manner to the perovskite by Förster resonance (or FRET). This protects the perovskite from high-energy photons, and therefore a priori improves light stability, with little energy loss.
The thesis work will focus on
- integrating MOFs into the perovskite layer, either as a surface treatment or as a mixture of suspensions
- Materials studies (in particular advanced studies using XPS and UPS)
- Favrication of single-junction devices and then tandem devices with silicon sub-cells
- Study of lifetime under illumination (continuous, cycling) with associated characterisations (electrical measurements, photoluminescence, etc.).

Melt grafting of polyolefin applied to reparable and recyclable photovoltaic panels

Solar panels are multi-materials assemblies constituted of photovoltaic cells that contains numerous precious metals (metal silicon, silver), high quality and therefore costly-to-manufacture glass that protects the cells, and a polymer film acting as binder, called encapsulant. These encapsulants are mostly thermoplastics that are reticulated during the manufacture of photovoltaic panels, which makes their dismantling and recycling difficult today.
CEA develops new materials to bring recyclability to renewable energy production systems, such as photovoltaic panels. The thesis revolves around the development of new encapsulants that allow improved recyclability of photovoltaic panels through a reversible reticulation system. In a first step, the melt grafting (extrusion, internal mixer) of polyolefins with molecules of interest will be studied in terms of grafting efficiency and kinetics, and impact on polyolefins properties such as thermal, optical, and structural properties. In a second step, a reversible reticulation will be triggered using the firstly grafted molecules. The impacts of this reticulation on the material thermal, mechanical, optical properties will be characterized. The application of the material as encapsulants will be the final aim of the thesis, and small demonstrators of photovoltaic modules using the material will be performed.

Nanodiamond-based porous electrodes: towards photoelectrocatalytic production of solar fuels

Among nanoscale semiconductors, nanodiamonds (ND) have not been really considered yet for photoelectrocatalytic reactions in the energy-related field. This originates from the confusion with ideal monocrystalline diamond featuring a wide bandgap (5.5 eV) that requires a deep UV illumination to initiate photoreactivity. At the nanoscale, ND enclose native defects (sp2 carbon, chemical impurities such as nitrogen) that can create energetic states in the diamond’s bandgap decreasing the light energy needed to initiate the charge separation. In addition, the diamond electronic structure can be strongly modified (over several eV) playing on its surface terminations (oxidized, hydrogenated, aminated) which can open the door to optimized band alignments with the species to be reduced or oxidized. Combining these assets, ND becomes competitive with other semiconductors toward photoreactions. The aim of this PhD is to investigate the ability of nanodiamonds in reducing CO2 through photoelectrocatalysis. To achieve this goal, electrodes will be made from nanodiamonds with different surface chemistries (oxidized, hydrogenated and aminated), either using a conventional ink-type approach or a more innovative one that results in a porous material including nanodiamonds and a PVD-deposited matrix. Then, the (photo)electrocatalytic performances under visible illumination of these nanodiamond-based electrodes toward CO2 reduction will be investigated in terms of production rate and selectivity, in presence or not of a transition metal macrocyclic molecular co-catalyst.