Visualizing charge movement near organic heterojunctions with ultrafast time resolution via an induced Stark shift

We introduce a method to monitor photoinduced charge separation processes in organic donor-acceptor heterostructures. This approach utilizes a transient Stark shift of the exciton band of a molecular J-aggregate, deposited as a thin probe layer adjacent to the organic heterojunction. The high temporal dynamic range of this approach, from 100 femtoseconds to nanoseconds and longer, enables the entire charge separation process to be followed in both space and time. More broadly, this method can be applied to characterize photoinduced charge injection and separation processes in different materials and architectures, where sub-picosecond time resolution is needed at high spatial resolution. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3694287]