Overview

Research in the Mohammed group is directed towards fundamental understanding of carrier dynamics in a variety of solar cell systems including semiconductor quantum dots, polymers and perovskite solar cells with the aid of cutting-edge nanotechnology, ultrafast laser spectroscopy, and four-dimensional electron imaging. These characterizations will provide valuable input in the engineering and optimization of these solar cell devices. In our laboratories, we are using various ultrafast spectroscopic techniques (transient absorption, fluorescence up-conversion, time-resolved vibrational spectroscopy, flash photolysis, time-correlated single photon counting) with a time resolution going from a few tens of femtoseconds (1 femtosecond = 10-15 second) to several nanoseconds and 340-1600 nm spectral range. In addition, we are currently establishing four-dimensional scanning ultrafast electron microscopy that can take time-resolved images (movies) at the nanometer and femtosecond scales. This powerful technique is based on the fact that after the bombardment of the specimen by the pulsed primary electron beam, secondary electrons can be emitted and collected only from the nanometer surface region owing to their low energy and small escape depth, thus providing a direct probe of surface phenomena in real space and time. The central concept of using such pulsed photoelectron packets for imaging enables the direct visualization of the carrier dynamics at the interfacial contact of the solar cell systems through real-space imaging with very high temporal and spatial resolutions.