Magnetic field effects in doped kesterites and perovskites for photovoltaics applications

Abstract:

The currently established photovoltaic technology, based on crystalline silicon (c-Si), suffers from high manufacturing costs, and intensive research is being conducted by the scientific community to further improve its efficiency, or to devise new materials to replace silicon altogether. The goal is to lower the cost-to-power ratio to levels that make photovoltaic technologies appealing for ultralarge-scale deployment.

In line with Milestone M2C2, Target 39, of the PNRR program, our consortium proposes an innovative concept for solar cell design, which couples two different and very promising classes of nanostructured materials, namely kesterite (CZTS) and Yb-doped lead halide perovskite (Yb:LHP). We plan to investigate the potential of a CZTS-based cell by adding a Yb:LHP nanoparticle overlayer. The latter is able to absorb photons in the UV portion of the spectrum, where the CZTS base layer shows a drop in photon conversion, and to downconvert them via a quantum cutting process that affords yields approaching 200%.

In addition we will study in detail the occurrence of magnetic field effects in magnetically doped kesterites and Yb-doped lead halide perovskites in view of their photovoltaics applications. Concerning the CZTS research line, we aim at tailoring and exploiting an innovative one-pot solvothermal synthesis of kesterite sensu strictu and Cu-, Fe-, doped CZTS at the lab scale. The identification of the main valence states of transition metals in the synthetic products, and of their ideal/unideal distribution in the structure and the corresponding effects on properties relevant for photovoltaics applications will be obtained by a tailored advanced characterisation.

After thorough optimization, a final attempt to scale up the synthetic route will be operated. This step will afford nanoparticles with the best performing combination of structure, chemistry and function, to improve the capabilities of the original solar cell design proposed here. Concerning LHP, we will prepare both undoped and Yb-doped and Yb,Ce-codoped nanocrystals, CsPbX₃ (X = Cl, Br, I). Intermediate halide compositions will be targeted to optimize the band gap, whereas Ce will be used to introduce localized defect states that can act as starting points for the quantum cutting process. A detailed magnetic and spectroscopic study of these systems will provide a deeper understanding of the basic physics underlying the process of quantum cutting which is instrumental to the use of Yb-doped systems as down-converter in efficient photovoltaics. In particular, the investigation of Magnetic circular dichroism and Magnetic circularly polarized luminescence will allow us to analyze the effect of the application of a magnetic field over the luminescent properties of the perovskites, hitherto scarcely investigated. Magnetic field effects will also be investigated on a hybrid cell based on a CZTS base layer and a Yb:LHP overlayer.