Solar Materials

In view of the growing shortage of energy resources, one of the primary goals of photonics is to develop novel materials and technologies capable of harvesting solar energy. Broad varieties of so-called solar materials are used nowadays to implement the devices relying on photovoltaic, photothermal and photoelectrochemical mechanisms for solar energy conversion. Lead halide perovskites (LHPs) and transition metal oxides (TMOs) are promising materials in each of these applications.

ARPES on Lead halide perovskites

Lead halide perovskites are a novel class of semiconducting materials, which are believed to be a possible replacement of conventional materials (Si, CdTe, CIGS) in solar cells. LHPs offer comparable efficiencies at lower price and with more simple processing. The applications of LHPs in photonics go beyond light harvesting: they can be used in photodetectors, LEDs and lasers.

Figure 1. Schematics of perovskite structure: A cation (CH3NH3, CH(NH2)2, Cs), B cation (Pb, Sn), X anion (I, Br, Cl).

Our research focuses on one of the most fundamental properties of LHPs: the energy and momentum dependent electronic structure. The ultimate goal is to obtain a microscopic picture of the charge carrier dynamics induced by a photoexcitation. To accomplish such a task time- and angle-resolved photoemission spectroscopy (TR-ARPES) is employed. The experiments are performed at the Harmonium vacuum ultraviolet facility [1], on the ASTRA (ARPES Spectrometer for Time-Resolved Applications) end station [2], in the framework of LACUS collaboration at EPFL.

[1]        C. A. Arrell et al., “Harmonium: An Ultrafast Vacuum Ultraviolet Facility,” Chim. Int. J. Chem., vol. 71, no. 5, pp. 268–272, May 2017.

[2]        A. Crepaldi et al., “Time-resolved ARPES at LACUS: Band Structure and Ultrafast Electron Dynamics of Solids,” Chim. Int. J. Chem., vol. 71, no. 5, pp. 273–277, May 2017.