Periodic Reporting for period 1 - NanoEAscopy (Mapping Nanoscale Charge Separation at Heterojunctions with Ultrafast Electroabsorption Microscopy)
Reporting period: 2017-09-01 to 2019-08-31
Charge-separation is the key process in photosynthesis as well as in organic semiconductor. Organic photovoltaic devices are flexible and transparent, and showing increasing efficiency. Understanding charge-separation and charge transport shall provide us with proficient schemes for molecular design and device architecture to achieve unprecedented efficiencies. This work will directly impact society since it has the potential to deliver step-increases in the efficiency of light-harvesting devices that will reduce the cost of optoelectronic devices remarkably.
Overall objective of this project is to successfully optimize the ultrafast pump-probe microscope, a very fast camera, as a platform to directly image electron-hole separation at the in-plane organic heterojunctions.
Organic compounds, Perylene diimide (PDI) derivative and Pentacene (Pc), were strategically evaporated thermally on a glass cover slide such that in-plane PDI-Pc (donor-acceptor) heterojunction is materialized.
TAM clicks pictures of the charge-separation at the heterojunction at different times starting right from the beginning of the process till the end. Pump laser pulse excites the carriers and creates the charge carrier distribution at the heterojunction and probe pulse monitors the distribution as a function of time, defined by the delay between pump and probe pulses. By analysing the shape and size of the distribution, we calculate how fast and how far the charges (electrons and holes) move. Wavelike transport of charges is observed where charges can move up to more than 10 nanometres in less than 100 femtoseconds.
The findings were disseminated via several invited seminars and also in international conferences as poster presentations. An article on the technique development is recently published in Journal of Physical Chemistry Letters. A manuscript on direct visualization of charge separation at organic heterojunction is under preparation.