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I will review our recent investigations of semiconducting materials at the focus of optoelectronic research. We measure the surface of CH3NH3PbI3 single crystals by making use of two-photon photoemission spectroscopy. By these means, we explicitly discriminate the initial thermalization of the electrons from slower dynamical processes. The picosecond localization of excited electrons in degraded CH3NH3PbI3 samples is consistent with the progressive reduction of photoconversion efficiency in operating devices. In the second part of the seminar I will discuss the dynamics of hot carriers in InSe. The electrons excited by photons of 3.1 eV experience a manifold relaxation. First, they thermalize to the electronic states degenerate with the M valley within 0.35 ps. Subsequently, the electronic cooling is solely dictated by Froehlich coupling to phonon of small momentum transfer. Ab-initio calculations of the electron-phonon coupling are in excellent agreement with the observed dynamics.

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Luca Perfetti, Ecole Polytechnique, Paris-Saclay, France
Seminar room 201, Institute of Physics 2
Contact: P. van Loosdrecht