Time Resolved Photocurrent Measurements in NQD/Si Hybrid Structures

The ultimate goal of our photovoltaics research is to create a prototype solar cell based energy-transfer mechanisms from nanocrystals to Si substrates. For that purpose, we are developing measurement techniques to study ET-induced photocurrents in thin Si nanomembranes. We are aiming to resolve small, (< nA) steady state and time-resolved (on a ns scale and faster) photocurrents induced in Si substrates from just a monolayer of nanocrystals grafted on Si. Such fine characterization capability will allow us to precisely tune nanocrystal’s placement and will lead to rational engineering of nanocrystal multilayers able to absorb the majority of the sunlight and to effectively transfer exitonic energy into Si substrates where charges can be efficiently separated and extracted into external circuit.  

Our lab recently acquired instrumentation to resolve <pA currents in steady-state (HP semiconductor parameter analyzer) and we are building our experimental system to record time-resolved, small amplitude photocurrents in Si structures. Both time-resolved gated detection (Boxcar integrator) andfast, 4 GHz integrating scope with gated pre-amplifiers are available. We have developedSilicon-on-Insulator (SOI)-derived Si nanomembranes with lithographically defined metal contacts and back-gate geometry to be able to study ET-based (nano)currents. Our recent measurements of steady-state currents with nanocrystals excited at different laser wavelengths above and below absorption resonance, clearly show ET-induced photocurrents in Si substrates. More exciting experiments are to follow…