Josh Macdonald

Cohort 3



Charge transfer processes at inorganic/organic interfaces, the role of doping

"Transition metal dichalcogenides have recently become areas of major interest in physics research due to their unique electrical properties brought about by their stacked van der waals structure. In particular TMDC's anomalously high absorption at nm thicknesses and fast in-plane charge transport are promising properties for Solar PV. Of this category of materials, tungsten diselenide (WSe2) is attractive for photovoltaics as it has a tunable bandgap of 1.1-1.3eV - near the Shockley-Queisser limit maximum - and can be easily processed by CVD methods. TMDCs could be especially suitable for applications in BIPV, due to the flexibility and low weight that results from ultrathin devices. We will study the interface between WSe2 and organic semiconductors by performing optical spectroscopy from the visible to the far infrared range. We will evaporate a monolayer of semiconducting organic molecules onto a WSe2 sample grown by CVD. The level of doping in the n or p organic layers will be monitored by FT-IR spectroscopy by looking at the charge sensitive vibrations, on which we have extensive experience based also on modelling and impedance spectroscopy. The process of charge separation will be monitored by heterodyne pump-probe spectroscopy from the 300 femtoseconds to 3 nanoseconds time scale. The spectroscopy studies will be aiming to explain what occurs in real devices and, therefore, after the first experiments the investigated structures will be more similar to solar cells with both transport layers and electrodes. Through collaborations with the group of Alison Walker we will model the dynamics of charge separation at these hybrid interfaces using Kinetic Monte Carlo simulations."